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evolution Gives our Biodiversity

eSSentiALS

Bats evolved echolocation to prey on insects such as moths

Island without moths; Ecosystem low in diversity…today

Father and Son Sailing

The island once had many moths

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the Case of the Quiet island I was a young student studying biology in Wales when I talked with my father into sail- ing with me. I had seen my friend sail a small boat earlier in the season, and it looked fairly easy. So my father and I set off to visit an island that our family once vacationed on when I was a child. The wind was at our backs, so we zipped along toward the island with ease. I thought, “I should buy a sailboat and make this my new hobby; I am really great at sailing.”

We docked the boat within a few minutes and began walking the island. It was just a few miles around On an earlier trip I had noticed that the island had many different creatures – plants, birds, bats, and lots of moths, one of my least favorite insects. My father noticed that it was very quiet – very peaceful and a great place to read – I think he was telling me I should get away to this island and quit bothering him with my studies.

We hiked up its small hills and took leaves and plants for study. We noticed that there were very few insects buzzing around us. “How great,” I thought, “no bugs around to bother us.” I had always disliked the arthropods, all of the insect classes, in fact. I recalled times when deer flies bit through a shirt into my neck when I was gardening. “They are good for nothing,” I reminded myself, happy to be relieved of them for at least this walk. There were only small farms on the island, which consisted of quiet country- side cottages. Oddly though, on our walk there were neither birds nor insects to make noise–well, peace at last.

The island had developed a great deal of farming, and the crops looked very healthy. My father commented, “This is what England needs, productivity. Big farms like this one will make Britain strong again!” I had read in a journal article that two-thirds of Brit- ain’s 337 large moth species are in significant decline. It was evening, and I again appre- ciated that there were no moths buzzing around our heads by the lamplights on the road.

“A nice quiet night but where were the moths that I once watched in the lamps along the road?,” I envisioned, recalling their bulbous bodies. As a biology student, I knew that moths were an insect class, Lepidoptera, with 150,000 known species. Moths were not beautiful like butterflies and were pretty gangly, throwing themselves at lights. I would never be an entomologist, who studies arthropods for a living.

My teacher made us read an article reporting that there had been a 99% decline in common garden moths, Marcaria wauaria, in the past few decades. The total num- ber of large moths was down by almost 50% in southern England. Three species of

CheCk in

From reading this chapter, students will be able to:

• Explain the relationship between evolution, biodiversity, and society’s role. • Use moth population changes as an example of evolution and species changes over time. • Discuss the history of how life’s origins were discovered, using ideas on spontaneous generation. • Describe how natural selection leads to species changes. • Define the types of natural selection. • Examine the role of speciation as a cause of biodiversity. • Describe extinction and its role in biodiversity changes throughout Earth’s history. • Discuss and evaluate the evidence for evolution. • Use sexual selection to explain the development of organisms over time.

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Chapter 7: Evolution Gives our Biodiversity 237

moths had disappeared from southern England in the past decade: Orange upperwing, Jodiacroceago; Bordered gothic, Heliophobus reticulate; and Brighton wainscot, Oria musculosa. “Good riddance, life goes on without them; but I wonder why so many were gone?” I pondered.

When we started back to the coast, I realized the wind was against us. I didn’t really know what to do when the wind did not have our sail. My father and I struggled to keep the sail straight and steered helplessly through the waves that had developed while we were on the island. It had become a nightmare. I frantically tried to steer and pull as the boat went out of control. The boom hit my father’s head in the confusion. He yelled, “You idiot, you’ll kill us yet! Why didn’t you tell me you had never sailed?” He was bleeding and I felt terrible. How was I supposed to know that sailing could get so out of control? It seemed easy when the conditions were just right. It dawned on me that the slight shift in wind direction, much like one fluctuation in moth populations, could usher in significant change leading to disastrous effects.

Moths are an indicator species, meaning that the state of the environment is first indicated by moth population health. Fewer moths mean less food for birds and bats, which eat moths. Those organisms eating birds and bats also are affected. One change in the environment can have profound impacts on the whole ecosystem.

The island was quiet like the sea when we arrived. There were few insects and few birds to make sounds, but the quiet island had spoken – and it was quiet no more.

CheCk Up SeCtiOn

In the story, our character is at first happy about the loss of biodiversity on the island. By the end of the story, it dawns on him or her that there may be more to the quiet island. Changing environmental factors, much like sailing conditions, can be unpredictable and get out of control. Moths in England declined in numbers in part due to habitat loss: large-scale farming destroyed hedges lining smaller farms, an area where moths thrive; pesticides also were shown to kill off many moths.

Study the life history of the Marcaria wauaria, noting its prevalence, habitat use, and the pur- ported reasons for its decline in southern England. Some species of moths saw population increases in southern England. The least carpet moth increased by 75,000%. Research why this occurred: How might changes in moth prevalence impact on our society? Do you think the narrator in the story had a change of heart about moths, about the environment?

What Are the Origins of Life? Life originated about 3.5–4.1 billion years ago, giving rise to the great diversity of organ- isms we see today. The origins of our biodiversity emanate from a small set of species of prokaryotes. Stacks of sediment made by colonies of bacteria, called stromatolites, are evidence of our primitive ancestors. Found in Africa, Australia, and the Bahamas, stromatolite layers contain carbon from bacteria dating back to early Earth. Since Earth was formed 4.6 billion years ago, life began relatively early in Earth’s history.

How did life originate from our molten ball of Earth chemicals? Early scientific thinkers believed that life originated from nonliving matter. The idea that life appeared from nowhere, called spontaneous generation, was held firmly by scientists for many centuries.

Spontaneous generation

The idea that states that life appeared from nowhere.

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The 17th-century scientists hypothesized that organic matter in food automatically generated maggots and all associated life when coming into contact with air. (You can make the same observation if you leave food at room temperature for a long-enough period of time; you will likely see mold and flies at the least.) Then, Francesco Redi (1636–1697), an Italian naturalist, became the first to disprove spontaneous generation.

Redi devised an experiment that involved placing a piece of meat into a glass jar. The jar was covered with gauze, which allowed air flow to the meat but no other agents larger than the holes in the gauze. A second control jar was left uncovered to allow con- tact with any external agent. Redi’s experiment is shown in Figure 7.1.

Redi’s results showed that the gauze-covered jar did not have maggots, but that the uncovered jar did. Realizing that some other agent had caused maggots and not the meat itself, Redi’s experiment was the first to disprove the idea of spontaneous generation. We now understand that flies were the cause of new life on decaying meat, with maggots growing from eggs laid on the organic material.

There were no microscopes in the 1600s to view the developing fly eggs on meat. The mechanism for new species growth on food was therefore unknown. However, Redi was criticized because new growth spoiled foods in both his control and his experi- mental jars – we now know the bacteria of decay cause the food to spoil. Thus, debate continued on whether life could arise spontaneously. Scientists also sparred over what caused milk and beer to sour. French biologist, Felix Pouchet (1800–1873) believed that microorganisms spontaneously arose in some foods, such as milk and beer, which had the right combinations to create life.

Pouchet heated flasks of hay brews to 100° C. He sealed the flasks, but even though they were sterilized, bacteria formed. Pouchet thus concluded that organisms could arise from a good mixture of materials, as found in beer and other fermentation environments. He tried many times to sterilize the flasks, but in every case within a short period of time, he observed a sea of bacteria. Pouchet thus reopened the defense of spontaneous generation.

Louis Pasteur (1833–1895) proposed an alternate hypothesis, arguing that bacte- ria were everywhere. He claimed that Pouchet’s experiment was contaminated when he

JAR 1 JAR 2

Figure 7.1 Redi’s experiment. After covering jars, Redi determined that a covered jar does not lead to maggot formation on meat. It was a first attempt to disprove the spontaneous generation of life.

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Chapter 7: Evolution Gives our Biodiversity 239

placed lids onto the flasks. Pasteur designed special long-necked flasks to keep broth placed inside free from bacterial growth as he sterilized its contents. Air was still able to get through to the broth; this eliminated the criticism that life might not have air to breathe, as in Redi’s sealed jars. The lower part of the neck of the flask trapped the heavier dust particles and microbes. His flask design is shown in Figure 7.2.

With no external agent, Pasteur reasoned correctly that the “trap” in the neck kept out microbes, and no new life formed in his flasks. When Pasteur tipped a flask to allow broth to touch the trap, bacteria appeared in the broth in a few days. His rejection of Pouchet’s results brought Pasteur membership in and an award from the French Acad- emy of Science. Pasteur’s experiment showed how his critical thinking led to a solid disproof of spontaneous generation – and led to the birth of microbiology as a discipline.

Personally, Pasteur was a devout Roman Catholic. He performed the experiment to emphasize the sanctity of life. He reasoned that if spontaneous generation were true, then there would be no need for a creator God to exist. His disproof of spontaneous generation was actually a movement against atheism. It worked toward a resurgence of religious faith in the 1800s. While Pasteur promoted his work as an example of pure science, it may show how one’s personal beliefs, even as a scientist, influences thinking about scientific research.

The Pasteur–Pouchet debate illustrates how scientific arguments continue through the centuries. The germ theory of biology, which places a focus on sterile techniques to prevent microbial disease spread, led to important improvements in medicine. The wide- spread use of sterile techniques decreased deaths, especially during childbirth.

The origin of life is of continual interest to scientists. In 1953, physical chemists Stanley Miller (1930–2007) and Harold Urey (1893–1981) devised an experiment demonstrating that precursors to life could have formed from the right mixture of chem- icals. Conditions on early Earth were simulated in a glass tube containing methane, hydrogen sulfide, hydrogen gas, and water vapor. The experiment in Figure 7.3 shows the design of Miller and Urey’s experiment.

An electrode was placed in the glass tube which simulated X-rays, ultraviolet light, and lightning of the early Earth. The environment in Miller and Urey’s glass tube was an oxygen-free system, just like on early Earth. When an electric charge was applied to this primordial mixture of chemicals, organic molecules formed. Fats, sugars, proteins, and genetic material were produced from the simulation.

Organic molecules make up life, and as discussed in Chapter 2, are able to self- assemble based on their chemistry. It is hypothesized that droplets of organic material

Germ theory

The theory that places a focus on sterile techniques to prevent microbial disease spread, led to important improvements in medicine.

Figure 7.2 Pasteur’s experiment.

Nutrient broth is sterilized

No microorganisms grow

Dust particles, bacteria, and other airborne

materials trapped

Microorganisms thrive

Airborne bacteria can now reach

the broth

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formed from the newly made organic products. As shown in Figure 7.4, the droplets formed a sphere that was separate from its environment. This sphere of organic material is called a prebiont and was the first form of new life. It was capable of replicating, absorbing genetic material, and forming new prebionts. These new “cells” further devel- oped into prokaryotes found as fossils within stromatolites. But how did so much life originate from such a simple prebiont?

natural Selection and Biodiversity Take a moment to ponder the fact that living organisms, in all their magnificent diver- sity, emerged from a simple assortment of chemicals on early Earth. Chapter 1 discussed Darwin’s principles of evolution; we will expand on some of those principles here.

When populations have more individuals than an environment can support there is inevitably a struggle for survival. Individuals have varied characteristics, with some better able to survive than others. These more successful organisms reproduce more and thus have better reproductive success (RS), defined as the number of viable offspring

Prebiont

A sphere of organic material that led to first living cells.

Reproductive success

Is the number of viable offspring an individual produces.

Figure 7.3 Miller and Urey apparatus. Gases in the glass tubes reacted to form organic molecules, precursors to life.

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Figure 7.4 Prebionts. These tiny spheres share some characteristics of life, including a separate membrane to keep it distinct from its environment.

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an individual produces. The frequency with which genes appear in a population change based upon these different RS rates. Organisms with a successful RS increase their relative proportions of genes in a population.

The change in gene frequencies in a population, over time, is defined as evolution. However, evolution acts only upon phenotypes, or the physical characteristics of one’s genes. Those organisms with traits better adapted for a particular environment will increase in numbers. The driving force behind evolution is thus natural selection, or nature selecting for or against certain attributes. It results from an interaction between organisms and their environments. Consider the polar bear, Ursus maritimus, which has white fur. Over time, those bears with a light color as camouflage were better able to blend in with their snowy surroundings. Contrast the darker colors of the brown bear, Ursus ameri- canus, which blends better within darker forests of North America (Figure 7.5).

Their respective environments influence the phenotypic traits that are selected for and against. To illustrate, the dark color of a brown bear roaming the polar ice caps would stand out like a sore thumb, making it easy prey for its enemies and obvious pred- ators to its prey. Thus, different environmental conditions favor different phenotypes at different times. If the ice caps were to melt, becoming forests, polar bears would no longer have an advantage with respect to fur coloration. In our story, the characters wit- ness changes in moth populations on the island. Moth species thus experience a change in gene frequencies within their populations, with some decreasing and some thriving. With declines in the V-moth, Marcaria wauaria and extinctions of three moth species in England, Orange upperwing, Jodia croceago; Bordered gothic, Heliophobus reticulate; and Brighton wainscot, Oria musculosa, natural selection is at work. Changed environ- mental conditions, such as loss of habitats and harmful pesticides in farming, contrib- uted to moth species changes (Figure 7.6).

Why the changes in moth populations in England? Consider that currants and gooseberries, once very popular and found in many gardens, lost favor across house- holds. Currants and gooseberries are a big part of V-moth diets. Without easy access to these foods, V-moth populations declined substantially. On the other hand, some con- ditions favored certain species of moths. In fact, one-third of moth species experienced increased numbers in the region discussed in our story. The reason was the improve- ments in air pollution and acid rain led to a rise in lichens, which are fungi–algae colo- nies. Moth species that increased in numbers had one common feature – they all fed on lichens. This is an example of natural selection occurring before our eyes – changes in moth species in our opening island story due to a response from environmental factors.

Evolution

The change in gene frequencies in a population, over time.

Natural selection

The natural selection for or against certain attributes.

Figure 7.5 a. Brown bear. b. Polar bear.

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In order for natural selection to occur on a particular trait, three conditions must exist: 1) there needs to be genetic variation in a population; 2) variation in traits must be heritable, that is, able to be inherited from one generation to the next; and 3) individuals with one trait must have better RS than individuals with another trait. In the case of the British moths in the story, their characteristics must be different from those of other spe- cies in some ways, and these differences must be inherited for natural selection to work.

In addition to losing important food sources, the declining species differ in their appearance and in their habitat requirements from other moths. Large farms recently emerged, reducing their shrubby habitats. Without places to deposit eggs and food for their offspring, their numbers dwindled. In contrast, it is widely believed that climate change and increased temperatures allowed many of their competitor moths to colonize the island, thus forcing them out. The three moth species experienced low RS, given the changed environmental conditions, resulting in their extinction from England. Changes in the environment may be temporary, but if the gene frequencies within a population also change, sometimes evolution has irreversible results.

types of natural Selection If a person has a harmful trait such as porphyria seen in the story in chapter 6, it affects that person’s survival. If another person is a carrier for porphyria, then his or her phe- notype is normal, and natural selection does not affect survival. Natural selection acts only on phenotypes because the environment only works on those traits expressed by an organism. While nature acts on one’s phenotype, phenotype emerges from one’s genes. The genes within an organism give rise to its physical appearance. Thus, gene frequen- cies change when a population is evolving due to natural selection.

There are three types of effects by natural selection: directional selection, stabiliz- ing selection, and disruptive selection (Figure 7.7). Directional selection occurs when individuals at one extreme of the range of variation in a population have a higher degree of fitness. If a group of dogs is bred, allowing only those with an aggressive disposition to mate, the offspring are likely to exhibit more aggression. Vicious dog breeds are commonly used as attack dogs by owners. The idea that behavior can be modified by selecting for certain characteristics is a theme of behavioral genetics.

Directional selection

The process that occurs when individuals at one extreme of the range of variation in a population have a higher degree of fitness.

Figure 7.6 There are light and dark moths on both the light and dark trees. Which moths do you think are more likely to be spotted and eaten by predatory birds? Why? From BSCS Biology: An Ecological Approach, 9th Edition by BSCS.

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Chapter 7: Evolution Gives our Biodiversity 243

EvolutioN DoES Not CauSE thE BESt oRGaNiSmS to SuRvivE

Evolution is not the survival of the best organisms, only those best adapted to their particular surroundings at any one time. Evolution is a product of the pressure by nature to select out the weak and keep those organisms best adapted for a particular environment. The strongest do not always survive. Consider dinosaurs, which were very strong, according to fossil prototypes, but were selected out; they were not the best adapted at some point in the past. Dinosaurs are believed to have died as a result of a giant meteor impact that added dust and debris to the atmosphere, causing a cool down.

The extinction of dinosaurs is a hotly examined topic. There is a debate between geologists and biologists as to the cause of their extinction. It has long been held that an asteroid hit the Earth about 65.5 million years ago, causing a major shift in climate. Dust from the impact led to less sunlight, fewer plants, and thus less food for dinosaurs and other species. Fossil evi- dence dating back to that period shows higher than normal amounts of certain materials, including iridium, indicating meteor-like hits. The layer of soil con- taining these particles is known as the K–T boundary (Cretaceous–Paleocene boundary) and correlates with a high extinction rate for many species types. The large crater on the Yucatan peninsula is thought to be evidence for this meteor impact.

There is an alternate hypothesis that microbial infections spread through- out dinosaur populations leading to their extinction. Emerging theories of dis- ease or infection as the cause implicate a viral or other parasitic infection as the reason for the dinosaur extinction. The hyper-disease theory of dinosaur extinction states that a microbe evolved rapidly to kill off other living creatures during the time period. While weather-related or biological causes led to their destruction, dinosaurs disappeared from the Earth due to the forces of natural selection, despite their impressive physical strength.

Death from global infectious diseases has had major impacts on society more recently in human history. For example, over 70% of Native American Indians died due to diseases brought by Europeans and not through battles. They lacked a natural immunity to those infectious pathogens such as influenza, small pox, and bubonic plague. The power of epidemics to destroy human cul- tures and other species has historical grounding.

hyper-disease theory

The theory that states that a microbe evolved rapidly to kill off other living creatures during the time period.

Stabilizing selection occurs when individuals at the mean or average range of varia- tion in a population have a higher fitness. In human birth weight, for example, the aver- age newborn is 7.1 pounds or 3.3 kg. This is also the weight associated with the lowest infant mortality and is thus selected for in nature. At other ends of the spectrum, infants with a low birth rate suffer more health complications without the required body fat; and at the higher end, birthing is difficult due to the large size of the baby. Modern medical treatments are allowing greater variation in birth-weight survival.

In disruptive selection, individuals at extremes of the variation spectrum experi- ence higher fitness than at the middle. In fish, larger males are stronger and able to

Stabilizing selection

Occurs when individuals at mean or average range of variation in a population have higher fitness.

Disruptive selection

The process in which individuals at extremes of the variation spectrum experience higher fitness than at the middle.

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obtain females more readily. Oddly, smaller males, known as sneaker males, also have better chances of survival than those of intermediate size. Sneaker males are able to “sneak” into a nest and impregnate a female without the larger male detecting him. It is a peculiar strategy for survival and works to help smaller sized fish persist in populations.

In our story, certain phenotypes result from a winning combination of genes. To illustrate, a set of genes determines the odd pattern on the eyed hawk-moth, Smerin- thus ocellatus. Its coloration allows it to remain camouflaged along bark when it is at rest, and when disturbed, it displays a set of “eyes” that startle its predators, allow- ing it time to escape. As shown in Figure 7.8, a phenotype enabling greater survival chances for an organism such as the eyed hawk-moth increases those gene frequen- cies, causing the species to evolve that trait. Natural selection pushes changes in gene frequencies in certain directions based on their efficacy in an environment, allowing organisms to adapt.

Figure 7.7 Graphs showing three types of natural selection.

A. Stabilizing selection Normal distribution with both

extremes removed

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C. Disruptive selection Bimodal distribution with average size removed ©

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Figure 7.8 Eyed hawk-moth is hidden by its surroundings.

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Speciation increases Biodiversity In Chapter 1, a species was defined as a population of organisms that are able to inter- breed and produce live, fertile offspring. Speciation is defined as the process by which natural selection drives one species to split into two or more species. It occurs when the new groups of species cannot interbreed with each other. Their inability to mate is called reproductive isolation. Several conditions may lead to reproductive isolation: mating songs may be so different that organisms don’t mate; changes in the genetic composition of two groups of organisms may make their offspring unviable, as in the case of the ster- ile mule, which is the offspring of a female horse and a male donkey; and divergence of groups into new geographic areas may prevent members of the new group from mating.

It is likely that the eyed hawk-moth evolved from an ancestor that lacked “eyes.” This beneficial moth phenotype, its “eyes,” enabled greater survival. Those organisms with the trait lived on to become the eyed hawk-moth, while those without the trait were at a disadvantage. Other moths of the Lepidoptera family do not possess this unique phe- notypic advantage. They survive, with other adaptations to help their success. The result is a number of different species, each with differing characteristics.

How do new species emerge from an ancestral species? There are two types of spe- ciation: allopatric and sympatric speciation (Figure 7.9). Allopatric speciation refers to the development of new species when there is a physical barrier separating members of a group of organisms. You can remember this as “all apart” speciation, because groups of new species form when they are all apart in different environments.

When members of a population undergo different environmental pressures, new species may result because different traits are selected. Speciation arises due to mech- anisms that isolate groups, allowing nature to act. Natural selection works differently when there are different conditions in two distinct environments. The different environ- ments may lead to enough changes to develop separate species.

In the case of the changes in diversity of moths on the island in our story, if V-moths decline as a result of a loss of food, perhaps a set of survivors will persist. Perhaps these survivors inherited genes that enable them to eat lichens on the island or some other

Speciation

The process by which natural selection drives one species to split into two or more species.

Reproductive isolation

The inability to mate.

allopatric speciation

The process of development of new species when there is a physical barrier separating members of a group of organisms.

Figure 7.9 Allopatric speciation is shown above. When populations are geographically separated into differ- ent species it is termed allopatric speciation; when populations occupying different ecological zones develop new species, it is termed sympatric speciation. From Biological Perspectives, 3rd ed, by BSCS.

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food not in decline. This group may survive and thrive, while the non-lichen eaters die off completely.

V-moths in other parts of Europe, away from the island, might undergo selection pressures that are different from those experienced by individuals remaining on the island. Consider two groups of V-moths, one on an island in southern England and one in mainland Europe. When enough changes occur in each group’s genetic make-up, the two groups of the same species of moth might diverge, forming two new species. This phenomenon is called adaptive radiation, in which a population of a species changes as it is dispersed into a series of different habitats. Adaptive radiation often occurs after 1) the extinction of a competitor, which helps increase the size of a population of species; 2) finding a new habitat, also allowing a group of species to thrive; or 3) after new genes give new advantages to a group of organisms. In each case, adaptive radiation results in many species emerging from a common ancestor. Recall from Chapter 1 that adaptive radiation occurred when new species of finches developed on the Galapagos Islands.

Another form of speciation results in new species due to behavior patterns. When new species emerge while living within the same geographical areas, it is known as sympatric speciation. It may result from 1) changes in genetic material among organ- isms, as in polyploidy or extra sets of chromosomes in plants, 2) use of different aspects of the same habitat, preventing organisms from interacting with each other, or 3) inabil- ity to reproduce with each other. At times, reproductive barriers separate species by preventing them from mating with one another. In sympatric speciation, members of the same species no longer reproduce with one another, because of either a change in mating behaviors or use of different habitats for food, for example. Sympatric speciation occurred in the meadow grasshoppers, Chorthippus biguttulus and Chorthippus brun- neus. The two species are similar in body size and shape, but they are reproductively isolated. The calling songs of each to attract a mate of the opposite sex have different vibrations, so potential mates may not recognize each other. As a result, natural gene flow between groups ceases, and each group changes with its environment as a separate entity. In the field, the two species of grasshopper do not mate, but in the laboratory, members of the two groups are capable of mating with each other. These premating bar- riers to gene exchange occur simply due to one minor difference in vibration in mating calls between the two species.

extinction The development of biodiversity in our ecosystem is a result of speciation over a long period of time. However, as stated earlier, 99% of all species that have ever lived are now extinct. Extinction is defined as the loss of a species forever, with no remaining organisms to maintain its population reproductively. There have been five great extinc- tion periods in Earth’s history, each explained by environmental causes (Figure 7.10). The last great extinction period occurred 65 million years ago. The sixth great extinc- tion is occurring today, at 80 times the rate at which species go extinct as in nonex- tinction periods. Only 1–2% of all species became extinct in the past century, but their extinction is permanent. Human impacts are believed to be the primary cause of this new great extinction era. Climate change and habitat loss, seen as responsible for moth declines on the island in our story, are primary drivers of environmental change and spe- cies extinction. The trouble with modern extinction is that speciation processes are not replacing extinct species with new ones. In previous extinction periods, many hundreds of thousands of years passed with species lost and gained, but in the current human- derived extinction period, occurring only in the past few centuries, new species do not have time to emerge. The danger to our fragile ecosystem is human unwillingness to

adaptive radiation

The changes that occur in a group of organisms to fill different ecological niches.

Sympatric speciation

The emergence of new species while living within the same geographical areas.

Extinction

The state in which a species is lost forever, with no remaining organisms to maintain its population reproductively.

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EvolutioN DoES Not CauSE iNCREaSiNG ComPlExity

A misconception that evolution leads to increasing complexity is not supported. The best adapted creatures are often the simplest, and many complex organ- isms – for example, dinosaurs – have become extinct. As discussed at the start of this chapter, prokaryotes have been around for most of Earth’s history, 3.5 of the 4.1 billion years of the planet. Prokaryotes remain very competitive because of their simplicity in design. They contain very few organelles and very simple genetic information, with only a primitive nucleus, a cell membrane, and some cytoplasm. There are no fancy organelles as found in plants and animals. This limits the amount of things that can go wrong with these creatures. Evolution does not lead to perfect organisms, only those best able to adapt to our world.

Consider the old VW beetle, which had no air conditioning, no power locks, windows, or brakes. It ran and ran for decades without problems. The VW is much like a prokaryote. Alternatively, more expensive and complicated automobiles contain many features that can break down. Anyone who has had a check engine light turn on appreciates the aggravation in finding the small prob- lem causing an emissions issue. The complexity of humans and other creatures can be their downfall. Over 99% of all organisms that have lived on this planet are now extinct! Complex life does not necessarily survive better, and certainly, I would predict that prokaryotes will outlive humans by billions of years.

Figure 7.10 a. Record of mass extinction periods in geologic history; five mass extinction events in Earth’s history occurred in relatively short periods of geologic time. The latest and most rapid extinction period is blamed on human society and its effects on the environment. From Biological Perspectives, 3rd ed, by BSCS. b. Dinosaurs, such as this Triceratops became extinct at the end of the Cretaceous Period, roughly 65 million years ago. It is hypothesized that a large meteor hit Mexico, leading to climate changes that did not support the life of dinosaurs. From Biological Perspectives, 3rd ed, by BSCS.

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alter environmental conditions so that species can emerge. Perhaps creating and enforc- ing policies that limit climate change effects or curb habitat loss will slow the sixth great extinction.

In our story, it is easy to see how quickly environmental changes can have unin- tended impacts. Other species besides the moths - namely butterflies, have experienced declines in England as well. Obviously, with a 99% decrease in the number of Black Hairstreak butterflies, the species is on its way to extinction there (Figure 7.11). With over 2,500 moth species reported in England, of which 900 are described as larger moths, it is concerning that the total numbers of larger moths has declined 38%, overall. Many biologists have suggested that species declines could lead to losses in biodiversity and extinctions of other species.

In our story, the main character’s final realization that there is a delicate balance in nature is heartening. The character finally shows an interest in learning about declining biodiversity and its effects on the environment. While difficult to detect upon simple observation, species losses affect human society as well other organisms in unintended ways. For example, while some species of moths increased in numbers, most declined. Moths are pollinators and are a food source for animals such as birds, bats, and small mammals. Along with moth species’ decreases, butterflies, bees, and carabid beetles also are declining in number. Biologists point out that this might be a part of a greater contraction in biodiversity in the insect classes as a whole – that England is only a pro- totypic ecosystem suggesting larger changes.

Figure 7.11 The great decline in butterfly species in England. Many species of insects declined in 2012, with 300, 000 fewer sightings of butterflies in one year. Changing environmental conditions, including weather patterns such as increased rainfall are thought to be contributing factors.

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aRE DiNoSauRS ExtiNCt?

Yes and no . . . While dinosaurs as a set of distinct species have been removed from the community of life, their DNA is very similar to that of birds. In fact, many biologists argue that birds are direct descendants of dinosaurs. Feathers were found on dinosaur fossils as far back as 1860. This link between feathers and dinosaurs was found in over 20 species of dinosaurs. Studies of fossils from dinosaurs, namely the Tyrannosaurus rex, show that birds are more closely related to dinosaurs than to other organisms such as reptiles, amphibians, or humans. Through analysis of collagen fibers, ropes of proteins in the soft tis- sues of animals, genetic relatedness between bird and dinosaur species was shown. Obviously, dinosaurs are no longer roaming the planet (Figure 7.13). However, much of their DNA remains – in birds.

Figure 7.12 Ecosystem of island in story – each of these organisms will be affected by a loss of moth species – which means that many other species are also affected.

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Changes in biodiversity are difficult to predict; the moths in our story are food for many species of birds and bats, which are eaten by wolves, owls, and eagles, to name a few. A delicate balance is maintained in our ecosystem (Figure 7.12). While natural selection is natural, humans impacts are not.

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extinction and Biodiversity The majestic coral reefs of the tropical waters are the largest living creatures in the world.

Moreover, they provide large habitats for many ocean species. They are, however, in decline, and their decline threatens the species who live among them. They have been adversely affected by boating, pollution, acid rain, and change in climate. Much like the moths in our story, they are a marine indicator species showing oceanic health.

Corals are resilient to a degree; for example, even if a small portion (or polyp) of the reef is destroyed, the organism can survive. But given the variety of adverse conditions they face, they are slowly dying, and when they die, so will many of the other species that inhabit them.

Skeletons of coral reefs, made of calcium carbonate, are a major component of the soil of the many archipelagos and islands in the tropics. Because coral reefs are so immense, they are not likely to die off from single isolated attacks. Many features of living systems are adapted for their survival (Figure 7.14). Coral reefs are large, living edifices but their survival is not guaranteed.

Coral reefs are just one example of how people often react to changes when it is too late. Our story showed how declines in moth populations could lead to a rocky sea of change for the environment, as the characters experienced in their journey are back from the island. Will it take a seaside sailing expedition for us to see how fragile our environment is?

evidence for evolution The extinction and emergence of new species are not new in Earth’s history. Organisms have changed throughout their time on Earth, as shown in the evidence for their evolution.

Figure 7.13 Dinosaur extinction: Did a meteor hit the Earth and cause their extinction?

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The evidence for evolution is given by four sources: 1) modern day examples of evolu- tion – recent natural selection in organisms based on environmental pressures; 2) the f ossil record, which shows organisms of the past in rock layers; 3) homology, or common ancestry; 4) biogeography, or the way species are distributed; and 5) molecular evidence.

Modern Day evolution Organisms are exposed to environmental factors affecting their survival. We do not, however, evolve as individuals, changing with the times. Instead, evolution is a popula- tion concept. That is, it is change over time in the genetic composition of a population. An individual will not develop gills because the Earth becomes an ocean, as in the film Water World. Instead, one mutant human could be born with some sort of gills that help it survive. While far-fetched, such an adaptation would likely take generations to emerge within a population. Also, it would develop only by random chance. In fact, gills slits in humans are not likely to develop. Usually, species go extinct and do not have the chance to survive with such a random mutation.

Evolution usually occurs slowly over many generations in life’s history. However, there are times when we are able to see it happen before our eyes. For example, bacteria reproduce very rapidly, within minutes in some species. The chance for mutation and adaptation among bacteria species is high within our lifetimes because one human gen- eration (25 years) equals many thousands of generations of a bacterium.

The mutations of H1N1 influenza virus are examples of an organism changing in response to the environment. Each year, its viral strains cause great suffering to the humans: 225,000 people are hospitalized each year due to influenza, and between 5,000 and 50,000 die of flu. In influenza-causing bacteria, recognition proteins on the surface of the membrane surrounding the influenza virus are either H, or hemaglutinnin, or N, neuraminidase. When viruses attach to their host to attack, they use these recognition proteins to dock. As they mutate, some forms of N and H are better able to resist our immunizations. It becomes a continual struggle for modern medicine and pharmaceu- tical research to keep these mutating viruses at bay. During some years, influenza hits harder, and the vaccines are said to be less effective than in other years. This happens because the N and H recognition proteins have mutated enough to withstand the effects of the vaccines. Influenza thus evolves before our eyes, forming new strains with new shapes of recognition proteins. As vaccines knock out strains of influenza, the survivor viruses, with new recognition proteins, become resistant to current vaccines.

Fossil record

One of the four sources of evidence for evolution, which shows organisms of the past in rock layers.

homology

Common ancestry.

Biogeography

The way species are distributed.

Figure 7.14 Colors of the coral reef: The vast and varied structure of coral reefs provide a habitat for a large number of species.

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Many species of bacteria have become resistant to antibiotics in a manner similar to influenza. Indeed, when penicillin was introduced in 1944, over 90% of strains of staphylococcus, a skin bacterium, were susceptible to the drug; by 1950, only half were, and today only 30% of staphylococcus strains are susceptible to penicillin. The infamous MRSA, methicillin-resistant Staphylococcus aureus is increasing in frequency in hospi- tals across the United States and is the cause of a variety of difficult to treat infections. These “superbugs” evolved from earlier strains that mutated to resist the ability of peni- cillin to damage their cell walls.

Biologists have also observed the ongoing evolution of two genuses, the Heliconius genus of long-wing butterfly and the Passiflora genus of passion flower plant, each evolving defenses against the other in a process termed coevolution (Figure 7.15). In coevolution, two organisms evolve traits based on their relationship with one another. The Heliconius butterfly lays its yellow eggs on the plant, and when the eggs hatch, the caterpillars eat the plant. The Passiflora evolved yellow spots on its leaves to mimic eggs. This strategy protects the plants since butterflies will not lay eggs on a plant that already has eggs on it. Over time, the Heliconius developed more acute vision that enabled the sharp-eyed individuals to detect the fraudulent yellow spots, and once again use Passi- flora as a nursery and food source for the larvae. In response, the Passiflora developed mutations that coded for extra-floral nectarines, which attracted ants onto the plant to defend it from developing butterflies. Ants eat the Heliconius eggs. This example of coevolution clearly illustrates a logical battle, using natural selection to develop new phenotypes between two species. However, changes are always based on random muta- tions that may or may not benefit each organism. In this case, plants with yellow spots were better able to survive and reproduce, just as butterflies with more acute vision were able to pass on their genes to offspring that had an ample food source. Because of these features, brought about through random mutations, some were more likely to survive than other individuals of the same species.

the Fossil record As the changes on the island in our story illustrated, characteristics of populations change slowly over time or rapidly. Some changes are slow enough that they are measured in eons – periods of geologic time. Geologists can track these changes by

Figure 7.15 Heliconium butterfly and Passiflora flower, a case in coevolution. This Heliconium caterpillar is feeding on a leaf of the Passiflora plant. Passiflora combats this by “faux” eggs. Heliconium eggs resemble those “faux” on the leaf of the Passiflora plant. These “faux” eggs dissuade the Heliconius from laying more eggs on the plant.

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inspecting the fossil layers of the Earth. The fossil evidence for evolution supports the predictions by Darwin that there were changes in species over time. The fossil record shows that prokaryotes did indeed precede all other life and that animal classes devel- oped in predicted taxonomic ways.

The sequence of development shows that first fish fossils, then amphibians, then reptiles then mammals, then birds, and finally humans emerged on Earth’s scene. This sequential order of appearance contrasted with the sudden creation hypothesis that pre- dated evolutionary thinking. Because fossils appeared over many hundreds of millions of years, the fossil record supports species change over time.

Paleontologists study the fossil record by measuring isotopes in the soil, dating layers back to when they were first deposited (Figure 7.16). In the past, before radioactive dat- ing of isotopes, fossils were dated based on how deep in the Earth they were. The deeper the fossil is, the older the layer of soil. However, earthquakes have disturbed layers, mixing fossils of different time periods. This was a primary criticism of the evidence for evolution, in which chronology in development of organisms was confusing.

homology Darwin hypothesized that all species evolved from a common ancestral species. Thus, he surmised that they would have characteristics similar to those of their common ances- tor. Indeed, scientists have since shown, through analysis of the fossil record, that Dar- win was correct. Among several types of evidence, scientists have studied homologous structures – similar structures found in different species (Figure 7.17). Bones such as the femur or thigh bone have the same general shape and relative size in many different species: humans, whales, bats, and birds, for example. While the fin of a whale is used for swimming and the wing of a bat for flying, the bones supporting these structures appear similar to human arm structure. Very often, evolution does not change design entirely. As discussed in Chapter 1, life is efficient, and when a good design works, it persists in many species.

At times, structures that once had a purpose but no longer appear to be functional, called vestigial organs, are found across different species. Snakes, for example, retain their vestigial walking bones such as a pelvis and leg bone, but no longer are able to

homologous structures

Similar structures found in different species.

vestigial organs

Structures that once had a purpose but no longer appear to be functional.

Figure 7.16 Soil layers and fossils found within them. There are many organism classes (from prokaryotes to modern humans) found in layers of the Earth, connecting their existence to different time periods. Note that the rocks with embedded fossils in this layer are from Whitby, England.

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walk. Our tail bone or coccyx, the final bone along our back, is our vestigial tail. The presence of vestigial organs is one sign of common ancestry.

Embryos also show commonality among related species. Pharyngeal pouches in the throat regions of vertebrates exist in embryos but not in adults (Figure 7.18). These pouches all appear similar upon inspection of the embryos but develop into either gills in fish or Eustachian tubes of the middle ear in humans. These structures show that efficient systems were worked out during our common embryological homology, but that different purposes evolved at some point in the past to direct development in other ways. A saying, “ontology recapitulates phylogeny” means that development of embryos (ontology) reiterates phylogeny (classification based on evolutionary evidence), and

Figure 7.17 Homologous structures in several species. These structures are similar because they are derived from the same ancestor. From Biological Perspectives, 3rd ed, by BSCS.

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Figure 7.18 Embryos of several vertebrates: salamander, chicken, chimpanzee, and human. The embryos are similar, passing through the same anataomical stages. Com- parative embryology is evidence that they arise from a common ancestor. From Biolog- ical Perspectives, 3rd ed, by BSCS.

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emphasizes that the similar embryologic structures show our common ancestry and thus is strong evidence for evolution.

Molecular evidence Molecular evidence is perhaps the strongest evidence of all for evolution. Consider that all organisms have the same genetic structures – DNA and RNA – to carry out life func- tions. The central dogma, DNA ➔ RNA ➔ protein, defines the common characteristic found in all living species. Moreover, all organisms use the same general form of DNA because it is efficient.

Molecular DNA data confirm findings from the fossil record and from analysis of homologous structures. Molecular analysis of DNA across species shows that the more DNA organisms have in common, the more closely related the species. Molecular biolo- gists and other scientists study amino-acid sequences in different proteins to demonstrate the degree of relatedness of species . . . Figure 7.19 shows the commonalty of amino-acid sequences in hemoglobin among several species. Common molecular homology is a strong confirming piece of evidence supporting evolution and relatedness of species.

Biogeography The geographical arrangement of organisms he observed first gave Darwin evidence for his ideas on evolution, as described in his Galapagos Island experiences (see Chapter 1.) Different beak characteristics in finches developed according to different environmental conditions on their respective islands.

When organisms in different environments develop the same characteristics, although unrelated, it shows that environment plays a major role in developing traits. Consider the sugar glider of Australia and the flying squirrel of North America (Figure 7.20a). Both organisms have a gliding lifestyle, with wing-like structures, but they are unrelated. They resemble each other but are only distantly related to one another. The sugar glider is more closely related to kangaroos, for example, while the flying squirrel is more closely related to other mammals. Sugar gliders and kangaroos are both marsu- pials, meaning that they complete their embryological development in a pouch. Flying squirrels are mammals, meaning that they complete their development internally in a uterus (Figure 7.20b). Sometimes similar physical appearance does not always imply closeness in two organisms’ evolutionary histories.

In our story, the island had a different climate and different species than in other parts of Britain. Different environmental conditions affect species differently based on their genotypes and thus they display different traits. Island biogeography often gives indications for evolution, because each island may have its own set of environmental

Figure 7.19 Similar molecular DNA comparisons across species. Genetic similarities in hemoglobin structure show very few base differences between humans and other species. Humans and chimpanzees show a very high degree of genetic relatedness. From Biological Perspectives, 3rd ed, by BSCS.

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Figure 7.20 a. Sugar gliders. b. Flying squirrels.

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conditions and organisms. Islands provide a good setting to study how organisms change over time. Island biogeography in our story gives first indications for how the larger ecosystem may change in the future.

evolutionary Design: there is no One right Answer As stated earlier in this chapter, evolution does not favor the strongest or the smart- est. Instead, it is based on a response by organisms to different environmental con- ditions at different times and in different places. A phenotype that works at any one

DoES EvolutioN ExPlaiN thE oRiGiN oF liFE oR thE oRiGiN oF thE uNivERSE?

Evolution does not explain either of these fascinating beginnings; in fact, evolu- tion only explains life after it evolved. The Big Bang Theory attempts to explain how the universe formed, from an extremely hot ball of gases some 13.75 billion year ago (Figure 7.21). The universe continues to expand in what is termed an inflationary epoch. Evidence for the Big Bang Theory is based on observations by scientists of movement and particle attraction. Matter is thought to be explod- ing and expanding outward, with our local sun a by-product of the Big Bang.

Physicists have indirectly detected that over 95% of the universe is either dark matter or dark energy. Dark matter is matter that is cannot be seen but only detected based on its gravitational pull and other evidence for its exis- tence. Physicists estimate that dark matter makes up 23% of the universe and its affiliated dark energy makes up 72%. Matter that is known to us composes only a very small part of the universe. It is strange to think that most of our universe is unseen and undetected by us.

The origin of life itself is traced to our beginnings – we are made of star- dust from the big bang, but before that time, there is no explanation of the forming of matter as we know it.

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Figure 7.21 a. The Big Bang is an explosion that is theorized to have begun matter and the universe. b. The TV show “Big Bang Theory”.

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time may be ineffective at another time. Evolution does not produce a perfect or even the best organism. Contrary to popular belief, evolution does not continually make species better. In fact, at times organisms can get much worse. Selection for large peacock feather to attract a mate actually hampers their lifestyle, preventing them from being able to outrun predators (Figure 7.22). On many farms, chubby chickens have been bred to be so large and tasty that they can no longer engage in sexual rela- tions. They need to be artif icially inseminated to produce live young, so selection in this case is artif icial and not natural. These are extreme examples of selection that decreases an organism’s quality of life. It is important to note that evolution acts to change organisms in response to their environmental conditions and not to make them better or worse creatures.

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Figure 7.22 Peacock’s large tails attract mates but often interfere with its ability to walk and carry out everyday functions.

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EvolutioN oF DiaBEtES: BlESSiNG oR CuRSE?

Diabetes is a sugar-sparing chemical system. It is not a new disease – it has been a genetic characteristic of humans since the origin of our species. Diabe- tes is, in fact, a useful and natural sugar-sparing characteristic that in prehistoric times conserved energy in times of starvation. Genes linked to diabetes are termed “thrifty” genes because they keep sugar levels high in the blood.

Diabetes is defined as a disease with higher than normal levels of glucose (sugar) in the blood (80–120 mg of glucose/100 mL blood). Under normal con- ditions, sugar in the form of carbohydrates is consumed by an animal, triggering the pancreas to respond by making more insulin hormone. Insulin stimulates the glucose to be ingested into body cells and causes the liver to store it. When blood sugar levels drop too low, the pancreas secretes the hormone glucagon, which stimulates the liver to release sugar. This negative feedback mechanism maintains homeostasis of sugar to around 90 mg/100 mL blood consistently through a lifetime (Figure 7.23).

Diets high in sugar and simple, refined carbohydrates are linked to the development of Type II diabetes because excess sugars “wear out” insulin receptors. Intakes of food with refined sugars, such as donuts and cakes, elicit a surge in insulin and a docking with cells in the body. This wearing-down pro- cess is known as down regulation. Each cell in the body has proteins on mem- branes to which insulin attaches. After docking, insulin causes the target cell to take up glucose. Diets high in sugars wear out insulin receptors and cause insulin resistance. Diabetes Type II (also known as adult-onset diabetes) works in this way; not to confuse it with Type I diabetes, which is an autoimmune attack on pancreatic cells that produce insulin. Both result in hyperglycemia (high sugar levels) but have very different mechanisms.

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Damage to tissues and organs occurs whenever glucose levels are too high or too low. In Type II diabetes, hyperglycemia results in diabetes, with insulin unable to allow sugars to be used by cells. This keeps blood sugar levels high, and cells do not obtain needed energy; thus they are starving. Clearly, these diabetic bouts damage nerves, blood vessels, heart muscle, and other organs. Alternatively, at low levels, hypoglycemia takes place, with individuals suffer- ing from weakness, disorientation, and even unconsciousness as the brain is deprived of needed sugars. This condition would be an evolutionary disad- vantage for prehistoric individuals who regularly missed meals because of the difficulty of getting food in harsh environments.

A mutation to prevent the conversion of glucose to glycogen was bene- ficial at one point in the past. The diabetes mutation maintained sugar levels during starvation conditions. These “thrifty” genes spare sugars in the blood, keeping it available for use. Consider the Neolithic diet, in which calories may be hard to find at certain times of the year; for example, when there is little game to be found. The individual with “thrifty” genes would benefit because normal circulating levels of sugar would be maintained longer for hunting and gathering to find food.

James V. Neel, a geneticist at the University of Michigan, discovered the “thrifty gene” sequence in some human populations. When faced with star- vation conditions, natural selection would have favored such gene sequences. The Pima Indians of Arizona, he found, were not only resistant to insulin’s effects of taking up sugar from the bloodstream but also retained more fat in storage. This helped the Pima endure longer periods of reduced food availabil- ity and starvation conditions.

The advantage of the “thrifty” genes to store more fat and keep circulating available blood sugar was an important survival strategy for populations during pre-agriculture times. However, in modern society, with availability of food much increased and a change from hunter–gatherer lifestyles that required more energy, people with “thrifty” genes are more prone to obesity and dia- betes. In fact, about one-half of the Pima Indians have diabetes, and about 95% of those diabetic individuals are obese. Are diabetes and obesity on the rise due to the dissonance between evolved metabolism and modern diets? Can lifestyle changes improve these maladies?

Studies indicate that a return to more traditional lifestyles and diets could improve the health of individuals. Pimas practicing traditional lifestyles in iso- lated parts of the Sierra Madre mountains of Mexico have significantly lower rates of diabetes (8%) and obesity (rare) compared to the modern U.S. Pima Indian population (Figure 7.24). This may be a case study to guide changes in our approach to combat obesity and diabetes. A diet rich in variety and whole grains, fresh vegetables and fruit, and low-fat protein sources has abundant support in science as a recommended diet.

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Figure 7.23 Negative feedback controls sugar levels. Insulin and glucagon control glucose levels in the blood to keep blood sugar at optimal levels. From Biological Perspectives, 3rd ed, by BSCS.

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Figure 7.24 a. Pima Indians in Sierra Madre Mountains in the 1800s. b. Pimas in Gallup, New Mexico, U.S., 2013.

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Summary Organisms change over time in response to the environment. Change is a part of life’s history whether it is expressed in the emergence of new species, an increase in numbers, a decrease in numbers, or complete extinction. Life’s origins harken back to early Earth conditions, but changes in species have occurred throughout its history. The moth popu- lations described in this chapter show how environmental factors affect species even in a short period of time. Natural selection leads to species changes with extinction as a final step in species loss and speciation as an outcome of adaptive radiation. There is ample evidence for evolution of species throughout Earth’s history.

Sexual Selection Natural selection not based on a struggle for survival but instead based on a struggle for the opposite sex is called sexual selection. In most animal societies, females choose their mates. They choose a male based on one of two factors: his available resources or his appearance. The more resources in a particular male’s territory, the more appealing the male. More resources indicate that the male will be better able to care for their young. A male’s appearance also plays a role in a female’s decision. If a male is more symmet- rical, then the male generally has a better genetic quality. Consider the quest for physical beauty, discussed in Chapter 3, showing the importance of appearance in finding a mate in human society.

While female choice is a primary determinant in mating, male aggression is also important. There are two forms of male aggression in sexual selection: passive sexual selection and active sexual selection. Passive sexual selection involves the development of charms and appearance to attract a mate. It is passive because it is used to attract rather than actively obtain a mate. The mating songs of grasshoppers (discussed earlier) and the feathers of a male Peacock are examples of passive sexual selection. Active sex- ual selection involves aggression by males to obtain a female (Figure 7.25). Antlers on deer, physical strength to fight, and tusks on elephants are examples of weapons used in active sexual selection. Sexual selection and the development of sex were discussed in Chapter 6 to show how variation helps species’ survival. Sexual selection drives the most fit organisms to be perpetuated in a population.

Sexual selection

Is the natural selection not based on a struggle for survival but instead based on a struggle for the opposite sex.

Figure 7.25 Active sexual selection is an example of Bighorn Rams fighting for dominance over females in the herd.

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CheCk OUt

Summary: key points

• Humans play a role in the evolution of other species within the environment, and are intrinsically linked to them.

• The process of discovering life’s origins point to conditions on Earth that were favorable for sponta- neous development of organic molecules and later, primitive cells.

• Natural selection favors certain traits and increases them in a population and disfavors other traits, decreasing them in a population over time.

• Natural selection may lead to speciation, which increases the number of species and thus biodiversity. • Extinction of species leads to permanent decreases in biodiversity. • Evidence for evolution is based on the current examples of modern-day changes in species, the fossil

record, homology, organisms’ biogeography and molecular evidence. • Sexual selection explains how organisms compete for the opposite sex to obtain the best adapted

offspring.

adaptive radiation allopatric speciation biogeography directional selection disruptive selection evolution extinction fossil record germ theory homologous structures homology

hyper-disease theory natural selection prebiont reproductive isolation reproductive success sexual selection speciation spontaneous generation stabilizing selection sympatric speciation vestigial organs

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Chapter 7: Evolution Gives our Biodiversity 263

Multiple Choice Questions

1. Which caused decreases in V-moth populations in southern England? a. Farming b. Acid rain c. Pollution d. Fishing

2. Which scientist used a long-necked flask to disprove spontaneous generation? a. Redi b. Pasteur c. Oparin d. Urey

3. Which best describes how moth populations changed in southern England in recent years? a. All moths declined in their numbers. b. All moths increased in their numbers. c. Some moths became new types of moths. d. Some moths increased in numbers and other moths decreased in numbers.

4. Disruptive natural selection may lead to: a. extinction b. speciation c. convergence d. directional selection

5. Which type of natural selection is most likely to cause adaptive radiation? a. Disruptive b. Stabilizing c. Unidirectional d. Bidirectional

6. Allopatric speciation: a. causes a new species to form. b. causes extinction. c. has the opposite effect of sympatric speciation. d. is less effective than sympatric speciation.

7. Which term is NOT associated with increases in biodiversity? a. Allopatric speciation b. Homology c. Adaptive radiation d. Sympatric speciation

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8. Two organisms are very closely related, with 98% of genes in common. This evi- dence for evolution is based on a. fossil records. b. biogeography. c. homology. d. molecular data.

9. In question #8 above, which provides the best evidence for showing the organisms’ relatedness? a. Molecular data b. Anatomical data c. Geographical data d. Speciation data

10. If two deer fight over a female using their antlers, this is an example of: a. passive sexual selection. b. active sexual selection. c. natural selection. d. adaptive radiation.

Short Answers

1. Describe how human society affects species diversity in your own neighborhood. Use one example of species that raises your concerns.

2. Define the following terms: adaptive radiation and disruptive natural selection. List one way how each of the terms differ from the other in relation to biodiversity.

3. Describe the experiments of two scientists: Francisco Redi and Louis Pasteur. Use a drawing to make the descriptions clear. Show your art work. How did each discover an aspect of spontaneous generation? How did their knowledge build upon one another’s?

4. Draw the Miller and Urey apparatus. What were the products of their simulation? How did Miller and Urey reignite debate on spontaneous generation?

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Chapter 7: Evolution Gives our Biodiversity 265

5. For question #4 above, how might you argue that life could emerge from nonlife?

6. List three ways evolution can be verified. Which piece of evidence is the most con- vincing to make the case that species today are a result of evolution?

7. Explain the process by which moth species declined in England in the past decades? How did some species of moths increase at the same time?

8. Some organisms base their choice for a mate on physical appearance. In barn swal- lows, an experiment showed that after making a male swallow less symmetrical, fewer females chose him. Explain how evolution favors this result in female choice. How will offspring change over time, given the results?

9. Name the type of speciation that results when a species cannot mate due to a change in their use of a habitat. Explain how it results in speciation.

10. A bacterial cell becomes resistant to a type of antibiotic. Predict the outcome for the population of this species of bacteria.

Biology and Society Corner: Discussion Questions 1. Moth populations in the chapter’s story show rapid changes in frequencies. Describe

two steps that the English government could take to help prevent unwanted biodi- versity loss in England. Are there any drawbacks to your suggested approaches?

2. How did Pasteur’s religious views affect his scientific outlook and methods? Are personal or religious views justified in propelling scientific thought? Why or why not?

3. If a person has a nonheritable form of intelligence that enables her to read peo- ple’s minds; what is this trait’s likelihood for changing the direction of evolution in society. Justify your answer.

4. Acid rain is a danger to some organisms and a benefit to others. In the moth species described in this chapter, explain how this is so.

5. An Internet site claims that people are getting smarter and smarter with each gener- ation due to evolution. Is this claim valid? Why or why not?

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Figure – Concept Map of Chapter 7 Big Ideas

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267

Before Plants and Animals: Viruses, Bacteria, Protists, and Fungi

EssEntiAls

Louis Pasteur Rabies virus

Glycoprotein Matrix protein

Phosphoprotein

RNA

Polymerase

Rhabdovirus (rabies virus)

The Death Cap Mushroom is the world’s deadliest poisonous mushroom

Yogurt is a product made by several types of bacteria through fermentation of sugars in milk

Many biofuels are made by bacteria

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the Case of the First Rabies survivor Andre played with his dog almost every day, but this time it was different. His friendly dog was strange; it seemed almost unaware of what was going on. Andre went to his beloved dog to help him get through the door of the barn. Suddenly, the dog lunged for- ward and bit Andre’s arm. This had never happened before.

In the course of the day, Andre’s mother noticed the bite on his arm. She inquired to find out what had happened. Andre explained, “The dog bit me. He was very odd, not himself, and looked like he had foam coming from his mouth.” “What’s wrong, mother?” Andre asked. His mother was crying, knowing Andre would have a horrible death that would come soon.

“Doctor, we brought the boy in just minutes ago. He was bitten by a rabid dog!” exclaimed the nurse. Dr. Louis Pasteur, a different kind of doctor who tried out-of-the- box techniques, was Andre’s last hope. Pasteur had a reputation, and many were afraid that his procedures were too far from mainstream medicine.

Dr. Pasteur was determined that no person would again die of rabies in the future. He had seen so many succumb to the infection. Pasteur worked in the 19th century, in a hospital that had none of the technology found in hospitals today. Still, Pasteur knew the symptoms of rabies that were awaiting Andre: fever, headache, tiredness, drooling and death. He was angry at organisms that he could not even see. “I cannot let another person die of rabies!” Pasteur protested.

Pasteur consulted with his colleagues, Dr. Vulpain and Dr. Grancher, to ask for their recommendation . . . should he attempt a drastic and experimental procedure, never done before? Both responded, “You should try it. Otherwise, this child will die; there is nothing to lose.” “But is it going to work – Is it even ethical to do?” Pasteur wondered. His research on rabies-infected dogs showed Pasteur that living infected dogs survived when injected with a vaccine made of ground up spinal cords from dead rabid dogs. But humans were not dogs, and Pasteur was nervous – “How macabre,” he thought, “to inject a human with ground up spinal cord from a dog.”

ChECk in

From reading this chapter, you will be able to:

• Explain how the diversity of organisms affects our health and society. • Discuss the discovery of pathogens, how they cause disease, and how this knowledge affected the

medical profession. • Describe the characteristics of viruses, types of viruses, and their related diseases. • Compare the lytic and lysogenic life cycle of viruses. • Describe the characteristics of prokaryotes, types of prokaryotes, their biological roles and relation-

ships with humans. • Describe the characteristics of protists, types of protists, their biological roles and relationships with

humans. • Trace the evolution of protists and fungi from ancient prokaryotes. • Describe the characteristics of fungi, types of fungi, their biological roles and relationships with

humans. • List and describe the diseases caused by viruses, prokaryotes, and protists and fungi, evaluating their

impacts on human society.

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The only other choice was death. Pasteur proceeded, injecting Andre with a spinal cord mixture. The night was long and emotional; as daybreak passed, Andre was still alive, perhaps a bit stronger than the day before. Each day for the next three months, Pasteur injected Andre with small bits of spinal cord. At the end of the treatment, Andre emerged as the first person in history to ever survive a rabies infection. Upon seeing Andre stand, Pasteur recalled the words of mathematician and scientist Blaise Pascal: “Man is but a reed, the most feeble thing in nature; but he is a thinking reed . . . All our dignity consists, then, in thought . . . by thought, I comprehend the world.” Pasteur reflected, “The frailty of the human condition is overcome by the strength of human thought.” He had succeeded in overcoming rabies with his planning and his thoughts. It was a glorious day for Andre and his family – and for biology.

Louis Pasteur’s 1800s discovery of the rabies vaccine shows the human struggle to use the power of the mind to overcome nature’s adversity. The seeds for medical progress and biological research are born of this quality, as shown by Louis Pasteur’s scientific reasoning used to cure Andre.

ChECk UP sECtion

This story embodies the essence of a way of thinking about the natural world, a movement from the power of physical strength to the power of the mind. This story highlights the struggle to overcome nature through innovation in the history of science.

The future of science lies in its past: the passion of the great scientists, their struggles against nature’s challenges, and their creativity in discovery. All point to the characteristics needed to propel scientific thought into our future.

Study the rabies infection, caused by the rhabdovirus, to determine its causes, symptoms, and treatment by vaccine in more detail. How were rabies and other microbial infections discovered, while being unable to see the organisms that cause it? What are some examples of modern diseases that are being studied to better humanity?

Discovering Pathogens and Ways to treat them The world of living organisms previously unseen by human eyes was discovered by microscopy. Anton van Leeuwenhoek described microbes, organisms that cannot be seen with the naked eye, very clearly and accurately in the 1600s as discussed in other chapters. This chapter focuses on the many organisms revealed by microscopy: viruses, prokaryotes, protists, and fungi (see Figure 8.1). Each of these groups has great variety; some organisms are beneficial to humans and some are harmful. Organisms that are harmful to humans are called pathogens.

Pathogens were not generally recognized as agents of disease until the late 1800s. The work of Louis Pasteur, described in our story, as well as that of other scientists, such as Robert Koch who studied tuberculosis in humans, pointed to microbes as infectious agents in plants and animals. Scientists showed that pathogens have a few ways to attack their host:

1) Some directly attack the host, destroying cells, as is the case for viruses and many bacteria. Viruses, including the rabies virus, invade cells and destroy them from the inside. They grow using their host’s resources as fuel and shelter.

Pathogen

Organisms that are harmful to humans.

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Figure 8.1 a. There is great diversity of life on Earth. Some major groups of organisms and their respective numbers of species are given in the figure. Insects comprise the largest proportion of species diversity. As seen in our story in Chapter 7, insects play an important role in our environment. From Biological Perspectives, 3rd ed. By BSCS. b. Some less appreciated forms of life; a. arachnids; b. fungi.

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2) Some pathogens cause disease indirectly, by producing substances that harm the host. For example, diphtheria is caused by the bacterium Corynebacterium diph- theria, which is inhaled and lodges in the upper respiratory tract. There it makes a toxin, or poison, that prevents human cells from making needed proteins and thereby kills them.

3) Some organisms cause damage by eliciting an immune response by the host. In some forms of pneumonia, the bacterium Streptococcus pneumonia causes such overwhelming release of fluids in response to its presence that the fluids fill the air sacs of human lungs, causing the host to have difficulty breathing. The inflammation caused by the pathogen causes damage instead of the pathogen itself.

4) Many pathogens cause multiple symptoms, as in the familiar cases of strep- throat (see Figure 8.2). The disease-causing agent for strep-throat is often Streptococcus pyogenes, which causes throat pain, a fever, and in 0.5% of cases, damage to heart valves, joints, and other tissues of the body. For this reason, strep-throat is considered more dangerous than a normal sore throat. Jim Henson, creator of the Muppets, died of infected heart valves from a strep- tococcus bout.

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Chapter 8: Before Plants and Animals: Viruses, Bacteria, Protists, and Fungi 271

By recognizing that some microbes caused disease, doctors and scientists began taking measures as far back as the 1800s to prevent their transmission. In medical pro- cedures, sterile techniques began to be used to reduce their numbers. Improvements in hygiene, hospital cleanliness, removal of public waste, and water treatment contrib- uted to cleaner surroundings as a result of recognizing microbial illnesses. In the past, for example, a major killer of women and children was childbed fever. It was spread by visiting doctors who carried streptococci from patient to patient as they examined them. The sterilization of instruments and introduction of hand-washing reduced patient deaths from microbes. Before these procedures became common practice, upward of 50% of children died within their first years of life. Since the advent of sterile techniques and vaccinations, the infant mortality rate has declined dramatically over the past cen- tury (see Figure 8.3).

The discovery of the first vaccination is described in our historical opening story. Bacterial and viral infections are treated and prevented through immunization, which

Immunization

The technique that uses dead pieces of disease-causing agents to strengthen immunity against a disease.

Figure 8.2 Strep-throat is a common infection. It is the inflammation of the tonsils and surrounding tissue at the back of the throat, resulting in redness and soreness.

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Figure 8.3 Infant mortality from 1900 to 2007. Dramatic decreases in infant mortality over the past century were a result of the discovery of antimicrobial techniques such as vaccines and penicillin.

1900 1920 19601940 1980 2000

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272 Unit 3: We Are Not Alone!

uses dead pieces of disease-causing agents to strengthen immunity against a disease. (Immunizations will be discussed in Chapter 15.)

In 1935, sulfanilamide, a new “wonder drug” was discovered in Germany, one of the first to control bacterial infections. Penicillin, which attacks cell walls of bacteria, was discovered by Alexander Fleming in 1940. Penicillin is a type of antibiotic, which is defined as any chemical that stops the growth of microorganisms (see Figure 8.4). Many antibiotics are extracted from bacteria or fungi that produce a natural defense against competitor microbes, harvested in antibiotics. Today, antibiotics and vaccines are also produced in laboratories. Antibiotics changed people’s lives and their life spans, as the most dramatic, large scale health improvement of the century.

Many microorganisms, such as the rabies virus, were undetectable under the micro- scope. They were discovered by indirect means, much as Pasteur detected and treated rabies. Because they cause so many plant diseases, viruses were first discovered in plants. Viruses are composed of combinations of nucleic acid, serving as their genetic material, and a surrounding protein coat. Their life cycle centers on their disease-causing ability, (discussed in the next section). Viruses cause many diseases ranging from the common cold to herpes, influenza, and cancer. There are a variety of types of viruses, each with differing shapes (see Figure 8.5).

The first virus-like organism to be discovered was found in studying PSTV, or potato spindle-tuber disease. PSTV is caused by a viroid, a simple virus that leads potato plants to produce long, gnarly, and deformed potatoes. This viroid also infects tomatoes, stunt- ing their growth and twisting tomato plant leaves. Viroids are also causes of disease in citrus trees, chrysanthemums, and cucumbers. Viroids are very simple, composed of only a strand of RNA – which leads scientists to the question: “Are viruses and viroids actually living organisms?”

Viruses: to live or not to live . . . Features Viruses are intracellular parasites, meaning that they invade host cells and live within them. They are not cells and are not included in the classification schemes of living organisms. They are obligatory parasites, unable to live outside of a host cell. Thus, they

Penicillin

An antibiotic obtained from the molds of Penicillium genus.

Antibiotic

Any chemical that stops the growth of microorganisms.

Intracellular parasite

Living organisms that invade host cells and live within them.

Obligatory parasite

Organisms that are unable to live outside of a host cell.

Figure 8.4 Penicillin is a blue-green mold that grows in a colony. Penicillin is a type of antibiotic produced by Penicillium, a mold. a. A penicillium colony. Penicillium produces round spores at the tips of its reproductive structures. It provides a special chemical, penicillin, that has saved millions of human lives. b. Chains of round tips at the ends of its reproductive structures are shown in this figure.

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are not considered to be living organisms. Viruses do not have an independent metabo- lism and cannot carry out life functions while outside of host cells.

Neither are viruses nonliving matter: they have genetic material, carry out some life functions, make proteins, mutate, and are able to reproduce. The structure of a typical virus includes a set of genetic material – either DNA or RNA – surrounded by a protein coat or capsid. The genetic material is simple, ranging from 1 to 100 genes along either a double or a single strand. A typical virus is shown in Figure 8.6.

Viruses are usually species-specific, with one type of virus affecting only one species of host. A human virus therefore cannot infect a cat and vice versa. The reason for this is that viruses use docking proteins to attach to surface receptors on host cells. As dis- cussed in Chapter 3, cell membrane proteins attach to docking chemicals. Viruses also use this docking system to attach to host cells. There are obvious exceptions, such as rabies in our story, in which Andre is bitten by a member of another species that trans- mits the virus. The docking and transmission between species is able to occur because rabies proteins match many species.

Some viruses have tail ends, shown in Figure 8.7, which enable them to attach spe- cifically to a host. The exception to the species-specificity rule occurs when mutated forms of viruses change enough to cross over to infect a new species. Scientists believe that this occurred in the spread of AIDS (acquired immunodeficiency syndrome), caused by HIV (human immunodeficiency virus), which mutated from nonhuman primates in sub-Saharan Africa in the late 19th or early 20th century.

Size of viruses

To show perspective, a virus size is very small, about .2 µm, while a bacterium such as Escherichia coli is 3 µm, and a human liver cell is large, at about 20 µm. Viruses often exist outside of their hosts as crystals. They remain able to be activated, so catching a virus from a door handle or a toilet seat is its mode of transmission. It remains dor- mant in the crystalline state and activates upon the first opportunity to enter into a host.

Capsid

The protein coat that surrounds structure of a typical virus.

Species-specific

Limited to or found in one species.

Figure 8.5 a. Morphology (shape) of some common viruses. b. Note that the rhabdovirus is bullet-shaped. It possesses receptor proteins on its coat (yellow buttons on the outside of the Rhabdovirus in image) which dock with host cells. Rhabdoviral DNA is spiral in shape and is protected within a protein coat.

Rabies virus

Glycoprotein Matrix protein

RNA

(b)(a)

Phosphoprotein

Polymerase

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Figure 8.6 A color-enhanced image of a T4 virus. It has a protein capsid head surrounding genetic mate- rial and helical tail with fibers and needle to insert its DNA. The virus uses its tail fibers to attach to a host bacterial cell wall.

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Figure 8.7 a. Microscopic view of a virus docking to host membrane protein. There is a specific-fit between a viral protein and receptors on the surface of host cells makes connections very exact. b. A virus then gains entry in a host cell, allowing it to conduct its strategies. In the figure given, viruses use the host cell’s machin- ery to manufacture new viruses.

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Whether airborne through the respiratory membranes of a human throat or via a cut in the skin, a virus returns to “life” when it enters another organism.

Some nonliving infectious creatures are prions, which are simple strands of pro- teins that ”liven up.” Prions cause brain infections such as mad cow disease and chronic wasting disease in deer. People who ingest meats infected with prions may exhibit no symptoms for decades, and suddenly prions reemerge, eating through tissues of the brain. No person has ever lived beyond one year after symptoms emerged from a prion illness. Prion diseases cannot be treated, and the best way to avoid their transmission is to eliminate brain or spinal cord meats from one’s diets. At times, such meats are ground up in hamburgers and in other processed food, with customers unaware of the true contents.

Viruses: the internal terrorist There is no magic bullet to kill a virus because most drugs do not work on a virus- induced illness. There are natural immune defenses, which will be discussed in Chapter 15, but viruses have unique actions that make them a difficult enemy. In addition, while antibiotics directly attack bacteria, viruses lodge themselves within our cells. This pre- vents their targeted destruction because host immune systems must then also destroy their own body cells. There are ways to attack a virus, discussed in the next section, but defenses against viruses are problematic.

Viruses are internal terrorists because they invade host cells, undetected by the body’s defenses, and incorporate themselves into its host’s genetic material. Viruses are successful much in the way that a spy infiltrates its enemy – by remaining unseen and unnoticed. If a host’s immune system detects a virus, it is destroyed and the virus is easily defeated. As long as a virus remains incognito, it can be successful at taking over its host cells.

There are two types of life cycles for viruses: the lytic life cycle, which results in a virus’s immediate destruction of a host cell, and the lysogenic life cycle, during which a virus inserts its genes into a host and waits for a time in the future to destroy the host. During the lytic life cycle, viruses attach to their host cells by grabbing onto their mem- brane proteins (see Figure 8.8). In the example of a bacteriophage, which is a virus that invades a bacterium – for example, an Escherichia coli bacterium, tail fibers on the virus specifically match the shape of host membrane proteins. Often the base of the virus con- tains special enzymes that bore holes to the inside of invaded cells. Some viruses contain a coil that acts as an injection needle to thrust the virus’s DNA or RNA into a host cell. Once inserted into a host, viral genes take over the nucleus of the cell, directing the pro- duction of hundreds and thousands of new viruses. Viruses are terrorists because they use the cell machinery of their hosts to destroy them. Viruses are then released, breaking their host cells – this is the “lytic,” or breaking, part of the cycle. The rabies virus seen in our story uses a lytic life cycle to rapidly kill its host. Andre would have suffered great pain and death from this process because damage occurs instantly when a virus breaks apart cells in the lytic life cycle.

During the lysogenic life cycle, a virus injects its genes into a host cell (see Figure 8.9). Viral genes are incorporated into a host’s DNA or RNA, and every time an infected host cell divides, viral genes divide along with it. It is an unstable relationship because at any one point in time, a set of viral DNA may activate and begin all of the steps of the lytic life cycle. The lytic life cycle is the same as the lysogenic life cycle, with one exception: the lytic process begins after a virus activates its genes within a host genome, while the lysogenic life cycle includes the period of dormancy of viral genes.

Prions

A small infectious particle believed to be the smallest disease- causing agent.

Lytic life cycle

A reproduction cycle which results in a virus’s immediate destruction of a host cell.

Lysogenic life cycle

A reproduction cycle during which a virus inserts its genes into a host and waits for a time in the future to destroy the host.

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Figure 8.8 Lytic life cycle of a bacteriophage invading an E. coli cell. During this part of a virus’s existence, it takes over the cell’s nuclear machinery. The virus in the picture uses a host’s DNA to produce more of its own genetic material and proteins coats, making many new viruses.

A. Attachment

Bacteriophage

Bacterium (host cell)

Host DNA

Viral DNA

B. Injection of DNA

Lysogenic cycle

C. Integration

Bacteria continue to replicate

switch to a lytic cycle, and phages kill the host cell

D. Multiplication

B. Injection of DNA

C. Replication of viral components

D. Assembly of new phages E. Lysis of bacterium host

A. Attachment

Lytic cycle

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Many factors can bring on the start of a lytic life cycle: sunlight, chemicals, or stress are three such factors. In the case of Herpes Simplex I, which causes fever blisters around the lips, anxiety or sunlight stresses may bring a virus out of dormancy of the lysogenic life cycle. This results in cell destruction and, of course, fever blisters. The focus of our story in Chapter 15 is on our immune system’s defenses against the herpes virus’s biology. Because the virus is lodged around nerve cells, fever blisters on lips are very painful, affecting nerve sensations.

You may remember these different life cycles as the one with “lytic” means to lyse or break open, and the one with lysogenic, refers to “genic” or genes that are dormant but may lyse or break a host cell at a later point.

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Chapter 8: Before Plants and Animals: Viruses, Bacteria, Protists, and Fungi 277

Figure 8.9 Lysogenic life cycle of Herpes Simplex I.

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some interesting Viruses Herpes Virus

Herpes viruses come in two types: Herpes Simplex I and Herpes Simplex II. Discussed above, Herpes Simplex I is not sexually transmitted, is localized around the lips of humans. and remains dormant in cells in a lysogenic life cycle (see Figures 8.9 and 8.10). Its viruses recognize skin and nerve cells because they come from the same embryo layer – the ectoderm – which will be discussed in Chapter 16. Stress brings out herpes because the immune system usually keeps it in check.

Herpes simplex II

A sexually transmitted and is characterized by genital sores.

Herpes simplex I

An inflammatory skin disease characterized by the formation sores around the lips.

Figure 8.10 a. Cold sores are symptoms of a Herpes Simples I infection. Eighty percent of adults are infected with the virus causing oral herpes. b. Genital herpes is sexually transmitted and is painful, which frequently recur in some individuals.

(a) (b)

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When a stress is placed upon the body, herpes reemerges from its lysogenic life cycle, entering the lytic phase. Herpes is transmitted by direct contact between two peo- ple. The sores it causes are composed of giant cells that are filled with white blood cells that ingest invaders and damaged materials. Herpes Simplex II is sexually transmitted and is characterized by genital sores (see Figure 8.10). They are recurrent and reemerge during stress on the body in the same way as Herpes Simplex I. Both forms of herpes viruses are delicate and cannot travel through the air.

Rhabdovirus

Rabies is 100% fatal and is an exception to host specificity; it is able to be transferred from one species to another, as described in our opening story. As mentioned earlier, the rhab- dovirus causes rabies, its structure is bullet shaped, and its DNA is helical. When a bite occurs, saliva containing the rhabdovirus transmits it into a new organism. The rhabdo- virus moves along the nerves of the body, up the spinal cord toward the brain.

In the brain, the rhabdovirus multiplies, causing symptoms and irreversible damage. Symptoms include fever, headache, hallucinations, intense muscular activity such as an arched back, and difficulty swallowing. Owing to the last symptom mentioned, a person with rabies shies away from water with a fear of swallowing. Foaming at the mouth, paralysis, and heart and lung failure leading to death are certain without treatment. In our story, before Pasteur’s discovery, society lived in fear of a bite from a rabid animal. It was a certain and horrible death. Rabies vaccination directly acts on the rhabdovirus, with special proteins or antibodies that attack viruses, stopping their action. Rabies vaccine is a form of immunization that acts directly on pathogens and without the help of a host’s immune system.

Rhinovirus

Less serious but nonetheless annoying is the common cold, caused by the rhinovirus. The rhinovirus kills ciliated cells of the upper respiratory tract in humans. The destroyed cilia are replaced with other cells along the throat. Once cilia are damaged, sufferers cannot adequately filter air. The mucous that forms in the common cold is a result of damage to these cells. The body attempts to cover up cell losses with mucous, leading to nasal congestion and respiratory upset. The common cold rarely kills, unlike the rabies virus in our story, but almost everyone is a victim of the rhinovirus because of its frequent occurrences and uncomfortable symptoms (see Figure 8.11).

Myxovirus

One of the illnesses caused by the myxovirus is influenza, which affects three to five million people worldwide each year and causes upward of 500,000 deaths. Its symp- toms include fever, muscle aches, pains, coughing, weakness, and fatigue. Sometimes a secondary infection with bacterial pneumonia occurs, the result of an immune sys- tem weakened by myxovirus. The myxovirus contains eight single strands of RNA, each able to mutate. This is a large amount of genetic material for a virus and explains in part how the influenza virus changes each year, with mutations in RNA sequences making new strains harder to vaccinate against. Myxovirus contains two types of pro- teins: neuraminidase (N), which digests through mucous membranes, and hemagglutinin (H), which enables the virus to bind with its host. Whenever genetic material of the myxovirus mutates, it changes its N and H proteins. Influenza infections have

Rhabdovirus

A bullet- or rod- shaped RNA virus found in plants and animals.

Rhinovirus

The most common viral infectious agent that causes common cold in humans.

Myxovirus

Any group of RNA- containing viruses.

Neuraminidase

A protein found in Myxovirus that digests through mucous membranes.

Hemagglutinin

A type of protein that enables Myxovirus to bind with its host.

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spurred pandemics, killing people worldwide. In the United States, more people died in the 20th century from influenza than from all of the major wars combined, as show in Table 8.1.

Papillomavirus

Human warts are benign tumors of the skin caused by viruses. Papillomavirus, the cause of human warts, contains double-stranded DNA surrounded by an icosahedral or 20-sided protein coat. Human papillomavirus (HPV) is associated with cervical cancer and is the basis of the relatively new vaccine against cervical cancer. It is spread by human contact, and in the case of cervical cancer through sexual transmission. There is debate as to whether or not to vaccinate all girls at age 11–12 to prevent most forms of cervical cancer. The debate occurs because it is a sexually transmitted infection, and people view teen-age sex through a variety of lenses. There was no debate when Pasteur saved victims from rabies, as described in our story – only celebration.

Papillomavirus

A group of virus that cause papillomas or warts.

Table 8.1 Influenza outbreaks occur due to mutated strains of the myxovirus. In the 20th century, there were more U.S. deaths from the 1918 flu outbreak than due to all of the major wars combined. Worldwide it is estimated that 30–50 million people died in the pandemic. Each year in the 20th century, the flu killed an average of about 36,000 people.

US Deaths 20th Century - Flu and War

WWI

WWII

Korean

Vietnam

Total

1918 Flu

Avg Flu Yr © K

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Figure 8.11 The common cold, caused by rhinovirus, is a nuisance but rarely kills its sufferers.

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THe WAR ON VACCINeS

Long forgotten are the benefits of vaccination to human society: fatalities from small pox fell from 2 million per year in 1967 to 0% by 1980; the Salk and Sabin vaccines prevented more than 5 million cases of paralytic polio; and vaccina- tions against infectious childhood diseases prevent more than 3 million deaths in young people each year.

Yet if you do a web search on the harmful effects of vaccines or the autism-vaccine link, thousands of sites are listed, all convincing their readers that vaccines are bad news. Hollywood stars such as Jenny McCarthy advocate for ending vaccines in the face of rising autism cases.

The risks and side effects of vaccines are unproven or extremely low. Many people do not recognize the benefits of vaccinations because they did not live through the many fears of life without them – polio, influenza, mumps, measles, hepatitis, small pox, to name a few. Our life span increased enormously from 38 years of age in 1850 to roughly 75–85 years today, in part because of vaccines. In the time before vaccines, people died early or during childhood or child birth without the benefits of vaccines to keep harmful microbes at bay.

The movement against vaccines is resulting in the reemergence of some diseases. For example, when an outbreak of measles swept across Europe in 2010–2011, 48,000 people were hospitalized and 28 people died unnecessarily. When less than 90% of the population is unvaccinated, dangerous spreading of disease becomes more likely. Over 80% of those infected in this outbreak were not vaccinated. In fact, being unvaccinated endangers the most suscepti- ble among us – children under 5 years of age.

The press reported two studies in the late 1990s that linked vaccines with autism: One was a false link between mercury-containing preservatives in vaccines and autism and a second was a discredited claim based on a study of only 12 children claiming that the measles-mumps-rubella (MMR) vaccine was linked to autism. The dangerous outcome of such reports is not in questioning the side effects of vaccines but the panicked decision by the public to avoid vaccination. It engenders a long-term danger that diseases may reemerge or harmful microbes may thrive and even mutate, and become stronger, making their prevention and treatment more difficult. There is little debate on the value of the rabies vaccine. Its direct link to surviving rabies, as seen in our story, is undisputable. We have come a long way, but perhaps we’ve come a bit too far for public health.

(source: Wall Street Journal, “Rolling Back the War on Vaccines,” February, 2013)

Oncovirus

Any virus that carries a gene associated with cancer is known as an oncovirus. It is able to insert its genes, called oncogenes, into a host genome, potentially causing cancer in the host and in the host’s offspring. Its genes are inherited, and this is a basis for evidence for the genetic cause of cancer. Oncogenes from an oncovirus become activated due to an event. The event might include an environmental stimulus like smoking or drinking, which causes oncogenes to turn on, resulting in cancer. Oncogenes could take decades to emerge or not show up at all in one’s phenotype, unlike the guaranteed death that rabies affords. Prevention of cancer at the genetic level of research holds the most promise in tackling the root cause of the disease.

Oncovirus

Any virus that carries a gene associated with cancer.

Oncogene

A normal gene that under certain circumstances can cause cancer.

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Figure 8.12 The oncogene theory. Oncogenes are mutations from normal genes which then cause cancer. For example, in human bladder cancer, small changes in the position of base pairs on a gene create oncogenes. As a result of a Chromosome #17 base pair change in the p53 shown in the figure, cancer develops. From Biology: An Inquiry Approach, 3rd ed by Anton E. Lawson.

Guardian of the Cell The p53 gene keeps tumors from forming. It either stops a damaged cell from growing into a tumor—or kills it outright.

The p53 protein locks onto genes, activating the cellular- defense system.

p53 PROTEINCHROMOSOME 17

3 If the p53 gene is healthy, it instructs the cell's protein factory to make p53 protein.

2 The p53 gene is located on the short arm of chro- mosome 17.

CELL

1 Every human cell (except sperm, eggs and red blood) contains 23 pairs of chromosomes.

P53 GENES

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The characteristics of cancer cells were discussed in previous chapters, but oncogenes point to their genetic origin. In a study by Weinberg, who isolated genes from bladder cancer cells, he found that only one base differed between normal cells and cancer cells: base #35 in normal bladder cells contained a guanine nucleotide and in an oncogene, base #35 contained a thymine nucleotide. Such a small difference genetically can lead to large changes in an organism’s health and survival. See Figure 8.12 for a visual descrip- tion of oncogene theory and the p53 oncogene.

Retrovirus

AIDS is caused by HIV, which destroys a human immune system’s fighting capabil- ities. HIV is a retrovirus, which is a virus containing RNA and the enzyme reverse transcriptase. Reverse transcriptase retroactively makes RNA into DNA, the opposite of the central dogma described in Chapter 5. The invasion of a host cell by HIV begins with its attachment to T-helper cells, which are key immune cells in humans. T-helper cells have a CD4 receptor on the cell membrane that matches with HIV-docking proteins. When the two attach, their membranes fuse, and RNA from HIV comes out of the virus and into the host’s cytoplasm. HIV is unique in its ability to convert its single-stranded RNA into single-stranded DNA, able to carry out life processes. Once viral DNA migrates to the nucleus, it uses host enzymes to make double-stranded DNA. In this form, it is integrated into the host’s genome, now “invisible” to the human immune system in a lysogenic life cycle. All progeny of T-helper cells are now infected with this dormant viral DNA. At a point in time, it reemerges and shunts into the lytic life cycle, causing the symptoms of AIDS. The course of the disease and its symptoms are shown in Figure 8.13 and Table 8.2. In the graph, you can see that at first the number of T-helper cells increases due to the host’s immune system fighting the infection. However, the numbers decline substantially as T-helper cells become more and more infected. With the immune system compro- mised, AIDS patients become susceptible to numerous illnesses, including pneumonia and rare cancers such as Kaposi’s sarcoma. Eventual death often results along with men- tal deterioration as the brain finally becomes infected. Its life cycle is slower than the rapid rabies advance on the brain that would have happened to Andre in our story.

Multiple drug treatments have result in marked improvement in the treatment of HIV and AIDS. A drug cocktail containing AZT, azidodeoxythymidine, inhibits reverse

Retrovirus

A virus containing RNA and the enzyme reverse transcriptase.

Reverse transcriptase

An enzyme that generates complementary DNA from a RNA template.

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transcriptase in HIV and has been shown to be effective in halting the disease course and extending life for HIV patients for many years.

Prokaryotes: the little things in life Features From an evolutionary perspective, the most successful kingdom is the prokaryotes, commonly known as bacteria. They have survived over 3.5 billion years, are adapted to almost every environment on Earth, and reproduce rapidly, allowing their colonies to change to adapt to new conditions in a short period of time. They are found in hot

Table 8.2 Symptoms of HIV infection.

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Figure 8.13 The decline in T-cells (immune defense cells, seen to the right) in AIDS patients over the course of the disease. After infection with HIV, T-cells are invaded by the virus. At some point, HIV enters a lytic life cycle and destroys T-cells. T-cells usually defend humans against infections. When T-cell numbers decline, susceptibility in AIDS patients becomes dangerous, almost always leading to death if left untreated. Infections occur later on in the disease’s course. From Biological Perspectives, 3rd ed by BSCS.

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springs, in deep-sea vents beneath the ocean, under arctic ice, in our guts, and on our teeth. As discussed in Chapter 7, their simple, efficient ways of dividing and mutating help them to change with the times and inhabit just about any environment.

Classification of the 4,000 different species of bacteria is based on appearance or upon metabolic, chemical reactions rather than evolutionary relationships, as opposed to naming systems in other organisms. There are testing methods, such as the API testing strips, used to determine which organic molecules are metabolized by bacteria. Micro- biologists classify bacteria into two different groups: archaebacteria, or ancient forms of bacteria, with only a few surviving branches; and bacteria, which were once called eubacteria, and are the modern prokaryotes. Continual developments in molecular tech- niques make the field of classifying bacteria changing. At this point, the two domains of prokaryotes are most commonly accepted.

Bacteria have small sizes compared to eukaryotes, with diameters less than 5 µm. A typical bacterial cell is many million times smaller than a human being, but it is much larger than the nanometer size of viruses such as the rhabdovirus of our story.

While tiny in size, prokaryotes outnumber all other life, making up more than 99% of all living creatures by sheer mass. Their circular genes are simple and, unlike those of eukaryotes, are not surrounded by a nucleus. They contain no organelles except for ribo- somes. Eukaryotes, which comprise all other life, are more complex. Eukaryotes contain all of the organelles discussed in Chapter 3 (see the comparison of cells in Figure 8.14). Their cells have genetic material surrounded by a nuclear membrane, heavier ribosomes, more complex DNA, and larger diameters ranging from 10 to 100 µm.

Archaebacteria

Ancient forms of bacteria, with only a few surviving branches.

Bacteria

Single-celled microorganisms that are found everywhere.

Figure 8.14 Comparison of prokaryotes and eukaryotes. The simple prokaryote has few parts but is able to outcompete eukaryotes because of its simplicity. The many organelles of eukaryotes (see Chapter 3) are shown in this figure with few in prokary- otes besides genetic material and ribosomes. From Biological Perspectives, 3rd ed by BSCS.

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Figure 8.15 Decomposition and recycling of nutrients by bacteria. Bacteria, along with other organisms, recycle organic matter, such as dead animals and plants, into reusable products. Several organisms described in this chapter work together to break down organic matter and return to useable materials in the environ- ment. From BSCS Biology: An Ecological Approach, 9th Edition by BSCS.

Decomposer food chain

1. mustard-yellow polypore (shelf fungus)

2. oyster mushroom

3. amanita 4. yellow morel 5. snail 6. sow bug 7. centipede 8. wood roach 9. springtails

10. mite 11. ant 12. carrion beetle 13. soil fungi 14. soil

protozoans 15. earthworm 16. inorganic

compounds 17. soil bacteria

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Only a few prokaryotes cause diseases in humans; most are beneficial to us and to the environment. Life on Earth would not exist without the activities of bacteria. Bacteria return nutrients to the Earth through decomposition (see Figure 8.15). Prokaryotes are used in the production of many chemicals, such as acetone and butanol, in fingernail polish, and cleaning agents. They make vitamins and antibiotics, milk, and cheese. As described in Chapter 6, they are used in gene technology to manufacture insulin for diabetics and human growth hormone (HGH) to treat dwarfism. In Chapter 4, we saw how the bacteria Lactobacillus acidophilus is used in yogurts through the process known as fermentation In fact, L. acidophilus bacteria are used to treat gastrointestinal illness because they are normal inhabitants of the human digestive tract. As they grow, L. acidophilus bacteria outcompete potentially troublesome bacteria in our bowels and produce lactic acid, which keeps other bacteria from growing. The roles of bacteria in human society are diverse, and many things in our environment require the workings of prokaryotes. While viruses like rabies create mostly human harm, we require bacteria for our existence.

shapes, sizes, and types The morphology (shape) of bacteria allows a general identification of its many strains. There are roughly 10,000 types of bacteria. They may be classified based on their metab- olism and their shape and arrangements. They may be round cells called coccus, rod- shaped, called bacillus, or spiral, spirillum. Bacteria may be arranged either singly or in groups. When bacteria are found in chains, they are classified with the prefix strep-; when they are found in clusters, they are classified as staph-. Figure 8.16 shows the shapes and arrangements of bacteria.

Morphology

The form of an organism that allows a general identification of its many parts.

Coccus

Round-shaped bacteria.

Bacillus

Rod-shaped bacteria.

Spirillum

Spiral-shaped bacteria.

Strep

The prefix given to bacteria that are found in chains.

Staph

The prefix given to bacteria that are found in clusters.

Figure 8.16 Common shapes of prokaryotes: Spiriulum (spiral), Baccilli (rod), and Cocci (round). The arrangement of chains (staph) and clusters (staph) of bacteria is also shown.

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MR. TOOTHdeCAy ANd MR. PIMPLeS ARe HARMFuL TO OuR HeALTH

Strains of Streptococcus are leading causes of tooth decay, such as Streptococ- cus mutans, which deposit acids on the enamel of teeth. Staphylococcus strains cause pimples on skin surfaces, as well as boils and other serious skin infec- tions. Some strains of Staphylococcus aureus, for example, cause necrotizing fasciitis or flesh-eating bacteria syndrome. While skin is not actually “eaten” by bacteria, it is destroyed rapidly by a spreading infection that, if left untreated by surgery and antibiotics, is fatal.

Figure 8.17 Gram-negative (pink) and Gram-positive (purple) bacteria cell walls. Each type of bacteria stains differently due to the thickness of their layers of peptido- glycans. Gram-positive bacteria have thick peptidoglycan layers while Gram-negative bacteria have thin peptidoglycan layers.

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Almost all prokaryotes have cell walls, like plants, but the structure of the cell wall is different from that of plants. Bacterial cell walls contain peptidoglycans, which are a type of protein known as glycoproteins. Sugars cross-link with each other to hold pep- tidoglycans together. There are two types of bacterial cell walls that identify bacteria as being one of two categories, based on using a dying technique called the Gram stain: Gram-positive bacteria are colored purple by the staining technique, and Gram- negative bacteria are colored pink. Gram-positive bacteria have simpler cell walls, with a thick layer of glycoproteins. This layer retains the dye from a Gram stain and appears pur- ple. Gram-negative bacteria have more complex cell walls, with less peptidoglycan, and gram stain washes away, making cells appear pink (see Figure 8.17). Gram-negative bacteria also have an outer membrane with lipopolysaccharides that protect their cells. Even though they are simple, bacteria are much more complex in structure than the rabies virus infecting Andre.

Peptidoglycan

Are a type of protein found in bacterial cell walls.

Gram stain

A dying technique that identifies bacteria as being one of two categories.

Gram-positive bacteria

A group of bacteria that retains the dye in Gram staining method of bacterial differentiation.

Gram-negative bacteria

A group bacteria that lose the crystal violet dye in Gram staining method of bacterial differentiation.

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Figure 8.18 Flagella arrangements around bacteria. Flagella may be arranged as single tails as shown in the image of the bacterium that causes cholera in humans, Vibrio chol- era. Bacteria cells also contain flagella grouped in tufts or as strewn throughout their surfaces.

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Penicillin works well in treating Gram-positive bacteria because it prevents cross-linking of peptidoglycans in the cell layers. Gram-positive bacteria walls thus fall apart due to penicillin. However, in Gram-negative bacteria, penicillin cannot move through the outer layer, preventing it from working to kill bacteria.

Many strains of bacteria have a capsule surrounding them, allowing them to prevent water loss and live in dry areas, such as in deserts and on our skin surface. Capsules are sticky and help bacteria to adhere to surfaces and to other bacteria.

Bacterial surfaces often have pili, surface hairs that allow bacteria to bind with each other. Through pili, bacteria exchange substances, including genetic material. This is bacterial sex; while not very elaborate, it serves to give bacteria greater genetic vari- ation. This exchange of genetic material through pili is known as conjugation. Pili are also used to help bacteria bind to surfaces. Neisseria gonorrhoeae, for example, fastens itself onto mucosal genital regions in humans. It is the cause of the sexually transmitted disease, gonorrhea. In fact, bacteria and microbes cause a number of sexually transmit- ted diseases.

Prokaryote nutrition More than half of all prokaryotes have motility. They move by means of flagella, fila- ments around their outer cell walls (see Figure 8.18). They also move by gliding, secret- ing chemicals on surfaces to move quickly. Flagella may be arranged as either scattered units, in tufts, or as a single length. Salmonella typhimurium, which causes the food- borne illness Salmonella, has scattered flagella leading to uncoordinated movement. Motile bacteria are characterized by taxis, which is movement toward or away from a stimulus. In chemotaxis, for example, bacteria move toward or away from food or oxy- gen sources. In phototaxis, bacteria move toward light.

Bacteria are also metabolically diverse. In phototaxis, some bacteria move toward light in order to obtain food via photosynthesis. These bacteria use a process of photo- synthesis that is quite different from plants. MIT Technology Review recently announced the bioengineering of photosynthetic bacteria to produce up to 30 times more sugar per

Pili

Surface hairs that allow bacteria to bind with each other.

Conjugation

The process of exchange of genetic material through pili in bacteria.

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acre than sugarcane plants for biofuel. When grown in transparent containers, these organisms use sunlight to produce ethanol from sugars to be used in cars as fuel (see Figure 8.19).

When bacteria use inorganic chemicals as energy, they are known as chemoautotrophs. These bacteria use inorganic molecules such as hydrogen sulfide and ammonia rather than food or sunlight to produce energy. They are independent, able to make their own food, and use carbon dioxide as their source for organic molecules. Chemoautotrophs do not require sunlight or oxygen. As shown in Chapter 7, the environment of early Earth provided an environment in which chemoautotrophs could have survived.

It is thus believed that these were the first organisms on Earth. Organisms in our intestines, which produce sulfur odors and methane gases, fall under this category. Nitro- gen-fixing bacteria, living in root nodules of bean, pea, and clover plants, use gaseous atmospheric nitrogen to produce ammonia (NH3) in their reactions to obtain energy. In the process, ammonia is made available as soil nitrogen, which is vital for plants. Most bacteria are heterotrophs, such as decomposers, which use dead organic matter for energy. They use dead matter to release carbon dioxide into the atmosphere as a product to be fixed later by plants in the Calvin cycle (described in Chapter 4).

Bacterial Reproduction Prokaryotes reproduce by splitting in half through the process of binary fission. A circular bacterial chromosome divides, attaches to its cell wall, and as the bacterial cell grows, the replicated chromosomes separate into opposite ends of the cell. Plasmids, small circular strands of DNA, also replicate, moving into two new cells. Daughter cells form after parent cell cytoplasm pinches inward.

Most of a prokaryote’s DNA codes for proteins, unlike in eukaryotes, in which 90% of the genes are not used in protein synthesis. Thus, binary fission is efficient and productive once a new cell forms. Fission can occur very quickly, within 20 minutes, resulting in over 20 billion cells in only 12 hours! It is able to maintain genetic variation through mutations, with so many chances for changes because of the many times a pro- karyote divides. As discussed in the previous section, conjugation also affords unique combinations of genetic material to recombine in prokaryotes.

Two other processes contribute to their genetic diversity. Transduction occurs when a virus, known as a bacteriophage, invades a prokaryote, inserting its genes into

Chemoautotroph

Bacteria that use inorganic chemicals as energy.

Binary fission

The process of reproduction by splitting in half.

Transduction

The process that occurs when a virus invades a prokaryote, inserting its genes into the host.

Figure 8.19 Biofuels made by crops of photosynthetic bacteria. A possible solution to the energy crisis? Shown, is a pond filled with photosynthetic bacteria in Hawaii.

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the host. Genetic recombination, as discussed in Chapter 6, is accomplished using a bacteriophage in the procedure. Insulin and HGH are manufactured in this man- ner. Transduction results in a transgenic prokaryote, with new genes added from the virus. Imagine a rhabdovirus transduced within a new bacteria. While fictitious, this would form a transgenic new organism, capable of causing rabies through bacteria transmission!

In addition, when prokaryotes absorb DNA from their environment, either through eating dead or dying bacteria or scattered matter, the genetic material is added to their own genome. This process is called transformation because the newly inserted DNA from the environment changes or transforms a bacterial cell into a new genotype (see Figure 8.20). Recall that Griffith's discovery of DNA in chapter 5 studied transformation in pneumonia-causing bacteria.

Prokaryote Diversity Archaebacteria

Archaebacteria are a type of prokaryote that is now classified as a separate domain from other bacteria are surrounded by cell walls that lack peptidoglycans, have unique cell membranes, contain RNA polymerase that resembles eukaryotes rather than other

Transformation

The process in which a newly inserted DNA from the environment changes or transforms a bacterial cell into a new genotype.

Figure 8.20 Transformation in bacteria. Foreign DNA from a dead bacterium enters its host bacterium. Once DNA is exchanged, this results in a new cell with dead DNA incorporated. This adds to genetic diversity in prokaryotes. New DNA is a new com- bination for organisms to use and their offspring to inherit.

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bacteria, and live in extreme environments, resembling early Earth conditions – in short, they appear different than other bacteria.

There are three groups of archaebacteria. The first group is the methanogens, which react to oxygen as a poisonous substance. Methanogens use hydrogen to reduce carbon dioxide into methane, CH4. They must therefore live in areas that have no oxygen such as marshes and guts of animals. Sewage treatment plants and landfills use underground methanogens to convert garbage to methane. This causes the typical sulfur odor of a landfill.

The second group of archaebacteria is the halophiles. Halophiles are “salt lovers,” which means that they are able to live in very salty conditions that few other organisms can withstand. Halophiles living in very salty lakes, such as Mono Lake in California (see Figure 8.21), use “pumps” to flush out the salt. Few other organisms can compete with halophiles in hypersaline areas such as Mono Lake in California, the Dead Sea in Israel, and the Aral Sea between Kazakhstan and Uzbekistan.

The third group of archaebacteria is thermacidophiles, which “love it hot and acidy.” They exist in temperatures from 60 to 80°C and in pH levels of 2–4. Sulfobus, found in sulfur springs in California, is one such organism that thrives in the extreme conditions of the hot springs. The extreme lifestyle of the archaebacteria leads scientists to believe that they were our most distant ancestors and the precursors to all life.

Bacteria

Most prokaryotes are bacteria, with varied morphology and functions. Some interesting bacteria follow, which show the variety of forms of bacteria that play a role in human health and the environment. One type of bacteria is the actinomycetes which have fil- ament strands and resemble fungi. Actinomycetes are decomposers recycling dead organic matter. As heterotrophs, actinomycetes rely on dead material to obtain food and therefore return organic materials back to the soil (see FIgure 8.15 for the decomposition process).

Cyanobacteria, such as Anabena and Nostoc, are photosynthetic and contain bacteriochlorophyll (chlorophyll pigment found only in bacteria). These bacteria pro- duce much oxygen in our atmosphere. Upon closer inspection, cyanobacteria contain large cells, called heterocysts, which contain nitrogen-fixing complexes that return nitrogen to the soil for plant use. Cyanobacteria reproduce by splitting at their hetero- cysts, breaking them open to produce new chains (see Figure 8.22).

Methanogens

Organisms that react to oxygen as a poisonous substance.

Halophiles

Are organisms that grow or live in very salty conditions.

Thermacidophiles

Organisms that thrive in strongly acidic environments at high temperatures.

Actinomycetes

A type of bacteria having filament strands and resemble fungi. They are decomposers recycling dead organic matter.

Cyanobacteria

Are photosynthetic bacteria and contain bacteriochlorophyll.

Figure 8.21 Mono Lake, California.

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Figure 8.22 a. Cyanobacteria microscope photo (Anabaena). b. Kingdom Monera: The evolutionary tree of Monera shows its vast diversity from a common ancestor. Cyanobacteria are only one example of the many species within the domains Archae and Bacteria. From Biological Perspectives, 3rd ed by BSCS.

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A GeRMOPHOBe’S NeW PeN

Metals high in copper content, such as brass, have been certified by the Envi- ronmental Protection Agency to be antimicrobial. Brass pens, doorknobs, and light switches have been used throughout the past centuries (Figure 8.23). These metals have long been known to work against diseases. Copper is an ancient disinfectant, killing bacteria, viruses, and other disease-causing agents, including six of the most common strains of bacteria such as S. aureus and E. coli. The more copper in a substance, the more it is antimicrobial in nature. Copper causes chemical reactions in microbes leading to oxidative damage: copper harms bacterial cell membranes and proteins, preventing microbe functioning.

In studies conducted by the University of Southampton, copper alloys were shown to eradicate influenza A, H1N1, and various stomach bugs within 10 minutes of dry contact on copper surfaces. This finding has motivated a switch to copper and brass products in some hospitals, to keep microbes at bay among the sick. Should we all purchase a brass pen?

Endospore-forming bacteria are Gram-positive, flagellated rods. They form endo- spores to endure harsh, dry conditions such as those found in deserts or dried-up marshes. In this form, spores as old as 250 million years, from Bacillus permeans, were found in the ancient salt sea underneath Carlsbad, New Mexico, and successfully revived. This ability to survive unfavorable conditions and revive in optimal ones marks a similarity between viruses and spore-bearing bacteria, but viruses like the rhabdovirus must find a host in order to reproduce.

Bacteria range in sizes, with the smallest known bacterium, the mycoplasma. They are between 100 and 250 nm in size, approaching some viruses in size. They lack a cell wall and are thus unaffected by most antibiotics, such as penicillin. Mycoplasmal pneu- monia is a serious illness caused by this bacterium.

Phototrophic anaerobic bacteria reduce NADP+ with electrons from H2S rather than H20, as seen in the process of photosynthesis described in Chapter 4. These bacteria do

endospore-forming bacteria

Are Gram-positive, flagellated rods that form endospores to endure harsh, dry conditions.

Mycoplasma

The smallest known bacterium.

Phototrophic anaerobic bacteria

A group of bacteria that do not release oxygen in their photosynthetic-like processes because the photolysis of water does not occur.

Figure 8.23 Brass acts as an antimicrobial agent. It has been used throughout history as pens, door knobs and handles, and as plates on light switches. Studies show that the chemistry of brass keeps microbes at bay.

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not release oxygen in their photosynthetic-like processes because the photolysis of water does not occur. Instead, they break-up H2S, which releases sulfur gas. This gas gives areas with these bacteria, for example, southern U.S. marshes, the characteristic smell of sulfur.

Enteric bacteria are found in animal digestive tracts. They are Gram-negative and include E. coli, for example. They thrive in conditions free of oxygen, without compe- tition from aerobic bacteria in other areas. Enteric bacteria are beneficial, providing vitamin K for humans, among other things.

Our interactions with bacteria should be studied in part to understand the human role in their life cycles. As seen in our story of Andre, our place in the ecosystem and possibilities for disease prevention are better implemented through researching life cycles of other organisms.

the Misfit kingdom: Protista Protists are eukaryotes, are mostly unicellular, have asexual and sexual reproduction, and move via cilia or flagella. Other than these common features, protists share few similarities, and may be viewed as a group of misfits because of their dissimilarities. Protista is the most diverse kingdom: its members have very different structures, metab- olisms, and ecological roles. They range in types of organisms, from the strange trum- pet-like Stentor to the giant kelp, which grows 150 feet “long at a rate of 2” per day. With 60,000 species of brown algae alone (of which the giant kelp is one), protista comprise a very diverse kingdom (see Figure 8.24).

Molecular evidence shows that Protista were the first eukaryotes, emerging roughly 1.5 billion years ago. About 1 billion years prior to their appearance on Earth, the oxy- gen revolution resulted from the photosynthetic activity of cyanobacteria. Prokaryotes evolved as some of the life forms able to use oxygen in energy processing. As dis- cussed in Chapter 3, the endosymbiotic model explains that eukaryotes then developed as prokaryotes absorbed oxygen-using creatures and evolved larger, more complex cells. Mitochondria and chloroplasts helped these new eukaryotes to obtain energy.

Figure 8.24 Images of Protista. They are the most varied of all the kingdoms. Some are motile and some sessile; some are plant-like and others animal-like. Depicted in this image is the sessile. Stentor, far left and the very active Paramecium, far right.

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According to the autogenous model of protist formation, primitive protists also evolved by invaginations of their membranes to form some of the membranous organ- elles such as the endoplasmic reticulum. The nucleus probably formed by invaginations around existing genetic material in primitive cells. This added benefit helped protists protect their DNA from environmental conditions. The complexity of protists helped them to survive and reproduce, competing with the simpler prokaryotes.

The first of these cells to develop were the Protista, which developed over 1 billion years after the oxygen revolution began. However, the protists of 1.5 billion years ago would not resemble those found today. Evolution and speciation have led, over these past 3 billion years, to speciation and the vast diversity in Protista. Biologists agree, however, that all other kingdoms – fungi, plants, and animals – originated from early protists.

Classification New techniques in electron microscopy, molecular analysis of DNA and new biochem- ical techniques make classification of Protista a changing field. The number of phyla, divisions of Protista and relationships within the kingdom are being debated. Biologists generally agree that there are three broad categories: 1) those that resemble plants – algae such as the giant kelp; 2) those that resemble animals – protozoans such as the stentor; and 3) those that resemble fungi – slime molds such as Physarum cinereum that creep across turf grass on lawns.

Algae Algae comprise a wide variety of what is commonly known as seaweeds. Algae are mul- ticellular organisms that are photosynthetic, and they contain a variety of pigments such as chlorophyll a and b (green), carotenoids (yellow-orange), phycobillins (red and blue), and xanthophyll (brown). These pigments increase the photosynthetic output of algae, making them responsible for over 50% of all oxygen production by the process on Earth. Pigments also give algae their definitive colors, which are used in their classification.

The giant kelp, mentioned earlier, is a member of the brown algae or phaeophyta, which has roughly 2,000 species. They are vast organisms, growing rapidly to form large regions of seaweed in temperate areas of the ocean in North America, South Africa, and the South Pacific. Giant kelp resemble sea forests with their dense mats of plant-like leaves, which provide a home to many hundreds of marine species – from other protists, fish and snails, to larger marine mammals such as the sea otter and gray whales.

Diatoms, or bacillariophyta, are a major producer of oxygen via photosynthesis. Diatoms live in oceans, as well as freshwater rivers, lakes, and streams. Their unique arrangements, due to complex silicon dioxide shells, make them a beautiful, ornate organ- ism (see Figure 8.25). Diatoms are part of the many protists that make up phytoplankton, which are all of the aquatic organisms that absorb carbon dioxide and release oxygen into the atmosphere. Phytoplankton form large and dense layers of organisms in water systems. Alone, they comprise about 25% of all oxygen production on Earth. Their eco- logical role in climate change and pollution is one of the most important dynamics of ecological study because of their contribution of oxygen in our atmosphere.

Other colors and forms of algae are found in bodies of water (see Figure 8.27): 1) Red algae, or rhodophyta, are red due to their phycoerythrin (red pigment), found along tropical coasts; 2) chlorophyta, or green algae, comprise about 7,000 species and are similar in cell structure and pigments to modern plants. Thus, they are believed to be ancestors to the first plants, discussed in Chapter 9. Chlorophyta are also a component of lichens, which are green algae or cyanobacteria living in association with fungi found

Autogenous model

The model that states that eukaryotes developed directly from a prokaryote by compartmentalization of functions of the prokaryote plasma membrane.

Algae

Are multicellular organisms that are photosynthetic, and they contain a variety of pigments such as chlorophyll a and b (green), carotenoids (yellow-orange), phycobillins (red and blue), and xanthophyll (brown)(algae is in bold).

Protozoan

A group of single- celled protists that resemble animals.

Slime molds

Organisms that live freely as single cells but form multicellular reproductive structures upon reaching a certain size.

diatoms

A single-celled algae that are a major producer of oxygen via photosynthesis

Phytoplankton

All the aquatic organisms that absorb carbon dioxide and release oxygen into the atmosphere.

Lichens

Green algae or cyanobacteria living in association with fungi.

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throughout most ecosystems (see Figure 8.26). Lichens are partnerships of organisms, with algae providing food from photosynthesis and fungi providing a physical place for algae to live. They are widespread – there are over 24,000 species of lichens, named by their type of fungal species, which is usually an acomycete fungus variety – and they can survive dry, harsh conditions, requiring only light, air, and a few minerals. 3) Chryso- phyta or golden-brown algae contain carotenoids and xanthophylls to give them their rich color. They form cysts that can survive very harsh conditions. They are colonial organisms and are biflagellated, with two flagella to propel them around; 4) Euglena or euglenophyta are unique in that they are both plant and animal-like. They contain an eye spot, which helps them to detect light and move toward it to carry out photosynthesis. Euglena, while able to make their own food, are also somewhat heterotrophic, requiring vitamin B-12, which they obtain through eating particles via phagocytosis.

euglena

A green single-celled, motile freshwater organism.

Figure 8.25 Phytoplankton, a type of diatom shown in this image. Diatoms serve an important role in aquatic habitats, from producing large amounts of oxygen to providing a food source for many organisms.

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Figure 8.26 There are over 24,000 species of lichens. Their algal layer produces food from sunlight and their fungal mycelium protects algae and anchors it to underlying substrates. Two species of lichens are shown on this branch.

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Protozoans Protists that have motility and are heterotrophic are characterized as protozoans. They include single-celled organisms such as the Amoeba, in the phylum Sarcodina. Amoebas are able to extend their cytoplasm, in the form of pseudopods (false feet), to move or obtain food. Sarcodina are the simplest protozoans, but their simple appearance does not mean that they are simple. They are able to behave in complex ways to obtain food, for example. When an amoeba senses its prey, through chemical detection, it extends its pseudopods toward and around its victim. It will also pursue its prey as long as it is close enough; amoebas judge the size of their prey, sending out just the right amount of pseudopod to ensure a meal (see Figure 8.28a).

Paramecia, in phylum Ciliophora, move using their fully ciliated bodies, by creat- ing waves in the liquid of their surroundings. They obtain food by beating their cilia to make currents to bring organisms into their oral grooves along the side of their cells (see Figure 8.28b). Paramecia are capable of both sexual and asexual reproduction.

Figure 8.27 A sample of Protista diversity: types of colored algae. A brown and red algae bed is shown beneath the ocean.

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Figure 8.28 a. An amoeba uses its pseudopods to move and also to engulf prey. b. Paramecium consumes food, usually entering through their oral groove.

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Those organisms in the phylum Mastigophora, such as trypanosoma gambiense, are parasites, causing sicknesses in the organisms they inhabit. Trypanosoma, which causes African sleeping sickness, is transmitted in the bite of a Tse tse fly. This illness may lead to kidney dysfunction, nerve problems, and eventual death. Trypanosoma is a reminder, as in our story, that microbes may cause serious disease among humans, with scientific research required to continually search for cures.

Another mastigophore is Trichonympha, which lives in the guts of termites, allow- ing cellulose, a plant substance, to be broken down for energy. This organism provides its host the ability to digest wood. However, most mastigophores are parasites, causing sickness in humans.

slime Molds Slime molds are often referred to as lower fungi because they resemble fungi.

However, they are different from Fungi in terms of their structure and biological processes. They are slimy because they release an oozing substance that flows along surfaces to engulf prey, such as other protists, bacteria, and fungi (see Figure 8.29). They are similar to fungi in that they both live in cool, dark, and moist places, such as forest floors and shower drains. All slime molds are heterotrophic and use spores to reproduce by forming fruiting bodies that release those spores.

Figure 8.29 Slime molds form fruiting bodies used in reproduction. The red-colored spheres in the image contain spores that are used to spread new mold.

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THe AGGReSSIVe AMOeBA

In a terrible twist of events, a young boy, 12 years old, was admitted to the hospital in central Texas. He attended a summer camp but went home “not feeling well.” He had been participating in water sports in a nearby lake to the camp, along with the other children. His mother took him to the hospital after days went by and he continued to have fever, loss of smell, and flu-like symp- toms. After admittance, several diagnoses were tentatively made: meningitis, pneumonia, and bacteremia. Then the horrible discovery in his cerebrospinal fluid: amoebas. The boy died only 5 days after being admitted to the hospital.

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A Favorite Fungus What is your favorite fungus? . . . Mushrooms for making soup? Yeast for bread? Penicil- lin for your illness? or perhaps Athlete’s foot, found in over 25% of the U.K. population? Each of these is an example of a fungus; they are found everywhere from feet to forest floors, usually in moist, dark places.

Features and types Many people think of mushrooms when they imagine a fungus. However, fungi are diverse, as shown in our examples. Fungi were once classified as plants, but structur- ally and chemically, they are more closely related to animals than plants. They do not contain chlorophyll, and their cell walls contain substances found primarily in animals. Their classification is not fully agreed upon among biologists, but most of their species fall into two phyla: Ascomycota, or decomposers, and Basidiomycota, commonly seen as mushrooms and puffballs. While most species of fungi are multicellular eukaryotes, some, such as yeasts are unicellular. Molds, which are difficult to remove from homes and cause poor air quality due to their spores, can also be beneficial, for example, as a source of the antibiotic penicillin. There are approximately 100,000 species of fungi

The temperature of the lake in Texas in which the boy was swimming in the summer of 2007 was 84.4°F (29.1°C). This was warm enough to support the life cycle of amoeba parasites. The story is based on a real report by Texas health authorities chronicling the events surrounding the death of a Texas boy. The infection was a result of Naegleria fowleri, a species of freshwater amoeba, which enters the brain and aggressively destroys it. While it is a rare illness known as amoebic meningoencephalitis, there are regular cases in which pond water enters into a patient’s nasal passages. Amoebas pass through the very small opening between the nasal passage and the frontal region of the brain, which houses the olfactory bulbs, used for smell. The parasite lodges itself there, right above the nasal passages, dividing and causing large lesions. Symp- toms first include a loss of smell or a sense that something is burning or rotting. Amoebas rapidly advance through the brain, dividing and damaging all areas until the victim’s death.

The course of the disease takes only between 3 and 12 days. Its survival rate, with aggressive medical treatment, is very low at only 3%. Other symptoms of amoebic meningoencephalitis include headache, fever, nausea, vomiting, and a stiff neck but later result a loss of balance, seizures, hallucinations, and death.

There have been only 160 cases since 1960, including two from using tap water through a neti pot irrigation system. The CDC (Centers for Disease Control and Prevention) report that warm pond water as well as some well water and municipal drinking water, may become infected with amoebas. While drinking infected water is harmless, when it travels through a person’s nose, then the potential exists for amoebic meningioencephalitis.

The disease remains a protist mystery, with unanswered questions: Why are some susceptible while others go unharmed, swimming in the same waters? How does the amoeba work to move across nasal membranes and into the brain? With such a small number of cases, is the public outcry about the illness an overreaction? Should people stop swimming in warm pond water?

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with many more expected to be discovered. Fungi emerged relatively recently in Earth’s history, about 500,000 years ago. An aquatic protist was most likely its ancestor.

The body of a fungus is generally composed of a mass of filaments called myce- lium. Each individual fungal filament is called a hypha, and the hyphae together create a mycelium mat (see Figure 8.30). These mats anchor deep into material that it is decom- posing in order to absorb its matter. Hyphae are one cell-layer thick, making it easy for fungi to absorb substances from their surroundings. A septum divides hyphae filaments into compartments, each septum having openings for communication. The cell walls of hyphae are composed of chitin, a polysaccharide found primarily in insect exoskeletons, their hard outer covering. Chitin is a strong substance, giving support to fungal cell walls. Chitin is rarely found in plants, an example of their distant relationship with fungi.

Fungi are not motile, but instead move rapidly through growth of their hyphae. Some fungi produce more than a kilometer of new hyphae in a single day. They have high rates of growth. For example, the yellow honey mushroom fungus, in Oregon grows so quickly that it covers an area of over 4 square miles. Their growth allows them to exert a great deal of pressure (1,200 psi) against other organisms, enabling them to penetrate deeply into plants, for example. Tips of fungal hyphae have the ability to penetrate hard surfaces, such as plant cell walls, insect coats, and even human skin. When given the chance, studies show that fungal hypha grow directly through human skin.

Fungi play a critical role in nature. As heterotrophs, fungi obtain nutrients through absorption of dead matter. Fungi eventually consume all living things. Thus, fungi act as decomposers, along with bacteria, to recycle organic matter through our ecosystem (see Figure 8.15).

Fungi also occur in relationship with other organisms, sometimes living on other organisms as in Athlete’s foot, ringworm, jock itch, and beard itch. Fungal diseases are very contagious because their spores survive for long periods on surfaces.

At times, fungi exist in a positive relationship with other organisms, as seen in our lichen example earlier in this chapter. In another symbiotic arrangement, root fungi or mycorrhizae live in root nodules of plants. Fungi benefit by obtaining sugar from the plant, and plants benefit by obtaining nitrogen and phosphorous from fungi, extracted from the soils around them. Many plant diseases are also fungal in origin, such as the

Mycelium

The mass of filaments that form the vegetative part of a fungus.

Hypha

Each of individual threads that make up the fungal mycelium.

Septum

A partition that separates two chambers of tissue in an organism.

Figure 8.30 The entire strand of fungal cells is knows as its mycelium. Mycelium is composed of hyphae that are divided into separate cells. The fungal cell’s components are shown in this figure.

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Figure 8.31 In the reproductive cycle of a fungus, spores form under the gills of mushrooms, forming new hyphae, able to mate and produce new fruiting bodies. Mush- rooms are fruiting bodies, producing spores for a fungus. Meiosis within gill cells of a mushroom produce haploid spores, which combine to form a new organism through the mating of compatible hyphae.

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fungus Cryphonectria parasitica, causing a blight that led to the destruction of the American chestnut tree.

Fungi reproduce both asexually and sexually. In asexual reproduction, a piece of mycelium breaks off, creating a new organism, in a process called fragmentation. In sexual reproduction, spores form in a tightly packed set of hyphae. A mushroom is actu- ally a reproductive structure produced by a fungus to develop and release spores (see Figure 8.31). Mushrooms occur as dikaryotic structures, meaning that their cells have two haploid nuclei that do not fuse. Some parts of a mushroom become diploid, with their haploid nuclei fusing. These diploid portions produce haploid spores through mei- osis, which are released into nature. These combine with other spores to result in a new diploid organism. Sexual reproduction gives more variation to fungal species, unlike mutations, the sole source of variation in the rabies virus discussed in our story.

Fragmentation

The stage in asexual reproduction in which a piece of mycelium breaks off, creating a new organism.

ROOT BeeR

When yeast ferments sugars, as discussed in Chapter 4, ethanol is made as a by-product. It is ethanol that gives alcoholic beverages their kick. When fermentation is stopped before alcohol fermentation really takes off, large

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summary The variety of organisms that are not plants or animals have many important functions in our ecosystem, but certain forms can also be harmful. Viruses have unique characteris- tics that classify them as an in-between living and nonliving state. They are intracellular parasites that seize a host cell’s machinery. Prokaryotes, much larger cells, carry out all life functions and play key roles in human health and in the ecosystem. They are our ear- liest ancestors evolutionarily. Their simplicity contributes to their success. Protists, the most diverse of life’s kingdoms, and quite a bit more complex than prokaryotes, emerged as our closest eukaryotic ancestors. They were the first eukaryotes, containing organ- elles and contributing to the evolution of higher plants and animals and fungi. Protista emerged about 1.5 billion years ago after the oxygen revolution made adaptations to use oxygen beneficial. Fungi emerged recently, only about 500,000 years ago, from protists. Fungi play a key role in the ecosystem, recycling dead matter. Fungi have many human uses ranging from medicines, wine, and breads to beer and delicate foods.

amounts of sugar are left and only small amounts of alcohol. The result is the popular drink root beer. It was originally produced from the root of a sassa- fras plant or bark. Roots are used as a source of many soft drinks. In the 19th century, farmers used yeast to ferment sugars in the sassafras root to make root beer that contained a small amount of alcohol. It was popular during their gatherings and a light-alcohol beer alternative.

The first commercially produced root beer was sold at the Philadelphia Centennial Exhibit in 1876, by pharmacist Charles Hires. It became quite pop- ular during the Prohibition era of the 1920s and early 1930s, as a substitute for beer. In 1960, the main ingredient of the sassafras root, was found to be carcinogenic and was banned by the FDA. Since then, artificial sassafras acts as a key ingredient, giving root beer its unique taste. Using and understanding natural products, as Pasteur did to discover a rabies vaccination, is a key to advances in health science.

ChECk oUt

summary: key Points

• Viruses, prokaryotes, protists, and fungi affect our environment and human health in many ways, from recycling chemicals and providing food and medicine to a variety of diseases.

• The discovery of the many non-animal/plant organisms showed their many characteristics, shared evolutionary history and role in the environment.

• Viruses are intracellular parasites, with two major types of life cycles: the lytic and the lysogenic. • Prokaryotes are simple and evolutionarily successful ancestors to eukaryotes. • Protista have three general groups: algae, protozoans, and slime molds, each of which contains a

variety of organisms with varied characteristics. • Fungi are decomposers; molds, yeasts, mushrooms, mycorrhizae, and lichens are types of fungi,

which are heterotrophic, and absorb nutrients from their environment.

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actinomycetes algae, red, green, brown, golden-brown antibiotic archaebacteria autogenous model bacillus bacteria binary fission capsid chemoautotroph coccus conjugation cyanobacteria diatoms endospore-forming bacteria euglena fragmentation Gram-negative bacteria Gram-positive bacteria Gram stain halophiles hemagglutinin herpes simplex I and II hypha immunization intracellular parasite lichens lysogenic life cycle lytic life cycle methanogens morphology

mycelium mycoplasma myxovirus neuraminidase obligatory parasite oncogene oncovirus papillomavirus pathogen penicillin peptidoglycan phototrophic anaerobic bacteria phytoplankton pili prions protozoan retrovirus reverse transcriptase rhabdovirus rhinovirus septum slime molds species-specific spirillum strep- staph- symbiosis thermacidophiles transduction transformation

Key TeRMS

• Fungi and Protista evolved from prokaryotes after developing membranous organelles, such as mitochondria.

• Diseases caused by organisms in this chapter include viral: rabies, herpes, influenza, cancer, the common cold; bacterial: necrotizing fasciitis, food poisoning, pneumonia; protist: amoebic meningio- encephalitis, African sleeping sickness; fungal: Athlete’s foot, ringworm, and jock itch.

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Multiple Choice Questions

1. Which organism is LEAST useful to human society and the environment? a. Virus b. Protista c. Bacteria d. Fungi

2. Which is a process by which pathogens work to harm host cells? a. They cause inflammation. b. They directly attack host cells. c. They produce toxins. d. All of the above.

3. Species specificity states that a virus has this many host species: a. 1 b. 2 c. 3 d. 4

4. The lysogenic life cycle holds viral _____ dormant within host cells: a. proteins b. genes c. carbohydrates d. fats

5. A cluster of spiral bacterial cells would be classified as: a. staphylococcus b. staphylospirillum c. steptobacillus d. coccus

6. Which represents a logical order, from early to later, in the evolution of organisms? a. protista ➔ fungi ➔ archaebacteria ➔ bacteria b. archaebacteria ➔ bacteria ➔ protista ➔ fungi c. fungi ➔ archaebacteria ➔ bacteria ➔ photosystem II d. protista ➔ fungi ➔ bacteria ➔ archaebacteria

7. A motile, eukaryotic, and heterotrophic organism is discovered on a distant island, with cilia surrounding its unicellular structure. Which is its best classification?

a. Slime mold b. Bacteria c. Algae d. Protozoa

8. Which term includes all of the others? a. Hypha b. Mycelium c. Chitin d. Septum

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9. In question #8 above, with which kingdom are the terms most associated? a. Protista b. Fungi c. Prokaryote d. Virus

10. In question #8, which process helps these organisms to obtain needed ATP energy a. Photosynthesis b. Absorption c. Exocytosis d. Species specificity

short Answers

1. Describe three ways in which prokaryotes benefit humans. List three ways in which prokaryotes harm humans. Be sure to list and describe each.

2. Define the following terms: transduction and conjugation. List one way each of the terms differ from the other in relation to genetic variation and biodiversity.

3. Describe the rabies experiment of Louis Pasteur discussed in the story. Research how Pasteur’s injections cured Andre. How do rabies immunizations work today?

4. Name three characteristics of viruses. Are viruses living or nonliving? Defend your answer.

5. For question number 4 above, list two types of viruses and describe their life cycles.

6. List the three groups of archaebacteria. How are they different from bacteria? Which would most likely be found in a hot liquid with a pH of 3? Why?

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Chapter 8: Before Plants and Animals: Viruses, Bacteria, Protists, and Fungi 305

7. Explain the structure and function of a mushroom. Use the following terms in your answer: spores, haploid, dizygotic, diploid.

8. A disease destroying mycorrhizae in forests concerns a group of biologists. Why are they worried about the effects of the disease on the ecosystem? On humans?

9. Explain the role of phytoplankton in our environment and in human society.

10. Diseases due to viruses are plentiful. Name three diseases caused by viruses in humans. Which are not species specific? Why?

Biology and society Corner: Discussion Questions 1. In order to prevent amoebic meningioencephalitis, measures should be taken to

reduce risks by government agencies. Research amoebic meningioencephalitis and list three recommendations you might make to improve public health with respect to the disease. Are your recommendations justified? Why or why not?

2. Louis Pasteur took a great risk with another person’s life. Give an example of an experimental procedure that you have heard about which is controversial. Are such risks in medicine justified? Why or why not?

3. The overuse of penicillin and antibiotics is well documented in medical research articles. Based on your research of these articles, why is it bad practice to prescribe antibiotics such as penicillin to patients with a common respiratory illness? Should you or your loved ones request these drugs during a patient-doctor visit? Why or why not?

4. Bioengineering of photosynthetic bacteria increases ethanol production greatly. Describe one way that this procedure might have unintended negative effects on human society and the environment.

5. A lumber company claims that dead trees need to be removed from forest floors to keep the forest clean and healthy. Defend their statement, and then also refute their statement. Use your knowledge of bacteria and fungi to formulate your answer.

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Figure – Concept Map of Chapter 8 Big Ideas

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649

Unit 5 A Small Hole Sinks a Big Ship –

Our Fragile Ecosystem

CHAptEr 17 population Dynamics and Communities that Form

CHAptEr 18 Ecosystems and Biomes

CHAptEr 19 Biosphere: Life Links to Earth

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651

population Dynamics and Communities that Form

Cheryl is a model

The cane toad (Bufo marinus) has taken over large parts of Australia’s ecosystems. It is considered an invasive species

Cane toads copylating. Toad sex is external and the male mounts the female

Toads are everywhere, as an invasive species that has a high rate of reproduction because they lack natural predators to keep their population numbers in check

Her prince has arrived!

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the Case of the terrible toads Plop, Plop – into her drink! “What just fell into my drink?!” Cheryl called out. Cheryl, the partier did not like toads or frogs or anything slimy or warty. Cheryl was a model, tall with flowing blonde hair; and as such, she had no use for amphibians. She left the United States last night for a great holiday get away to an island off the coast of Australia.

“How sheik,” Cheryl mused as her plane landed. On her vacation, Cheryl expected a beach hotel with hot days in the sand and hotter parties at night. At the airport, the taxi driver picked her up, quickly asking her, “Do you want to go out with me tonight?” Cheryl replied coldly, “I am sorry. I am here to meet my prince.” The driver was disap- pointed. However, Cheryl had an agenda. She hoped to meet celebrities on the island and start her acting career, now that she finished her days at the university. This trip was her emancipation from school.

As they drove in from the airport, down through the desert, and to the beach, Cheryl noticed a strange sight along the beautiful beachfront – there were warty creatures. They were hanging from the trees, jumping all over the roads, and hopping in unison like dense mats.

The road could no longer be seen and the driver simply ran the animals over, unfazed by their presence. Cheryl was aghast, asking the driver: “Driver, what are these things?” “The cane toad, of course, and they are here to stay.” he replied serenely. Cheryl demanded to him, “Turn back, we are leaving this place!” However, it was too late; the plane had gone and would not be back to the island for one week.

Cheryl did not do her homework about the island or cane toads before booking her trip. The cane toad had been introduced to Australia in 1935, with the hope that it would prey on the destructive cane beetles. About 3,000 cane toads were released into the wild. The experiment was, however, a failure in controlling the beetle populations.

Instead, the cane toad became a much larger problem. Within a few years, millions of cane toads swarmed Australia and continue today to be a pest organism. There are 200 million cane toads in Australia, and the government has identified it as a key threat to the environment and other organisms.

CHECk in

From reading this chapter, you will be able to:

• Explain how invasive species and changes in their populations affect human society and the environment.

• Describe the characteristics of populations, its demographics, and how populations are studied. • Define and describe invasive species, ecology, population ecology, logistic model of growth, expo-

nential model of growth, carrying capacity, fertility rate, age structure diagram, survivorship curve, ecological footprint, density-dependent factor, density-independent factor, niche, habitat, resource partitioning, biotic factor, abiotic factor, predation, herbivory, parasitism, commensalism, mutualism, and competition.

• Apply models of population growth in human and nonhuman populations. • Compare the two types of life histories and apply them to real examples using survivorship curves. • Describe the roles organisms play within their community. • List the types of population interactions within a community and give real examples.

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Cane toads, scientifically named Bufo marinus, appear ugly to many, including Cheryl. They are large, chubby, and have dry, warty skin. They breed easily, having fre- quent copulation. B. marinus is also toxic, affecting the heart muscle of those organisms that consume it, including humans. Cane toads cause the death of many types of native species to Australia. Many pets, cats and dogs especially, eat the toad and die from its venom. Cane toad venom is secreted as a milky liquid from its parotid salivary glands located over its shoulders.

Bufo marinus has no natural predators to keep their population in check. They are native species in South America and the Southern United States, but their natural predators keep their numbers manageable in those areas. Those organisms eaten by cane toads are also being depleted, such as a number of insects. Species consuming those insects are also endangered, with little food remaining after the toads enter into an area. Thus, interactions between the different organisms in Australia have been shifted out of balance. The cane toad is therefore a dangerous invasive species to Australia.

Cheryl saw (and was touched by) things from the sky, from the ground, and from the water. All over, the toad creatures rubbed up against her in ways she had never seen before. The cane toad became, very quickly, Cheryl’s worst nightmare.

That evening, the driver met Cheryl in the local bar. Cheryl sat with her drink, a cane toad and the driver at a table. Cheryl looked at the driver, the toad looked at Cheryl, and the driver looked at the toad. Cheryl looked angry. The driver addressed Cheryl the best way he could: “Here’s your Prince. Pucker up, Cheryl…”

CHECk Up SECtiOn

The cane toad in the story is considered an invasive species, which is any species not native to a region but grows rapidly due to lack of natural predators or parasites to keep them in check.

Over 4,500 invasive species have invaded the United States. Research the types of invasive species impacting the area in which you live or study. Be sure to describe the history of how the invasive species entered into the area and the techniques of eradicating the invasive species.

What changes have occurred in (a) society and (b) in the environment; as a result of the invasive species? How does it differ from organisms native to the region?

Ecology is based on Studying populations Order in a population In our story, invasive cane toads impact the environment and other organisms. They appear as a nuisance and repulse Cheryl on her vacation. However, their biological impacts on the island might be a bit more complex than just a mere bother to Cheryl.

How much land area will B. marinus take over? What can be done to slow its pop- ulation growth? What organisms are eaten by the cane toad? How will the toads impact other species, such as freshwater turtles and crocodiles? All of these questions are answered through ecology, the study of the interactions between organisms and their environments. The term ecology derives from the Greek words “oikos,” which means home and “logos,” which is translated into “the study of.” Together, ecology means the study of our home on this Earth.

Ecology

The study of the interactions between organisms and their environments.

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This unit studies nature and the environment and is divided into three chapters. In this chapter, we will explore how biology occurs within populations. The environment is orga- nized into different groupings (Figure 17.1). A population is a group of organisms of the same species living in an area. A population of organisms, such as B. marinus, for exam- ple, grows and is structured in ways that are studied by ecologists. In the latter part of this chapter, the community (aka biocenoses) is studied. A community is a set of populations interacting with each other.

In Chapter 18, we will study how the environment interacts with those communities, in a grouping called an ecosystem. All of the Earth’s ecosystems are collectively known as the biosphere, which will be the focus of Chapter 19, the last chapter in this unit. The components of the biosphere as well as threats to its health will be explored. Figure 17.1 shows the hierarchy of environmental organization from population, community, and ecosystem to biosphere.

Ecology is based on the dynamics of populations – a population is the basic unit of study in ecology. The ways a group of species grows, shrinks, and breeds, for example, show the dynamics occurring within a population.

Ecosystem

The interaction of the environment with a community of organisms.

Biosphere

All of the Earth’s ecosystems.

Figure 17.1 Hierarchy of environmental organization: individual, population, community, ecosystem, and biosphere of organisms such as the cane toad. The toad’s role within each of these organizations should be studied to help combat its invasiveness.

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Organisms of the same species inhabiting a specific area.

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Population ecology studies a population of organisms and how it interacts with its environment. It explores population patterns of growth and interactions with other spe- cies. B. marinus is treated through this chapter as a unit of study to explore: how its role in biology shapes the environment and other species around it. We will compare cane toad population growth to look at human populations. This chapter especially probes human population growth in its role underlying many ecological issues today.

population Demographics The rate at which a population grows and shrinks is measured in several ways. Trees are tagged to measure their arrangement in a forest and Americans have a census every 10 years. Both of these are methods to quantify and study a population. The data collected by ecologists about the statistics of a population of species is known as its demograph- ics. Population demographics tell us a great deal about how a population is structured in terms of age, size, and density.

Population demographics help scientists predict how populations will change over time and affect other organisms. A population size gives the number of organisms in a population, and a population density reveals the number of organisms per area of land in an ecosystem. For example, the total number of cane toads in Australia is over 200 million, but on the island in our story, there are fewer toads totally but they have a greater population density. Higher population density could have more impacts on the environment than sheer numbers. B. marinus patterns should be studied in greater detail to determine the answers.

A population distribution shows the arrangement of organisms of a population across a particular region. Most cane toads are clumped on the northeastern areas of Australia.

Whether a population grows or shrinks depends on four factors: the number of births (new born additions); the number of deaths (those leaving permanently); the number of immigrants (new organisms from other areas); and the number of emigrants (organ- isms leaving the area). Population growth occurs when more individuals are entering than leaving a population. It can be calculated by the following equation: Growth rate = (Births + Immigrants) – (Deaths + Emigrants). In Mexico, for example, a rapidly growing population is a result of higher birth rates than death rates. Death rates declined much more than birth rates in the 20th century, leading to a need for emigration to stave off even larger population increases.

In the case of finding ways to decrease the cane toad population, natural predators for the cane toad would increase its death rate. So far, this strategy has not shown much success because the cane toad is toxic to many predators, such as the crocodile that swal- lows a cane toad whole, but ingests enough toxin to kill itself. In another approach, by decreasing its birth rate, growth would slow as well.

Some studies look to introduce sterile males into populations to prevent births. This strategy has had limited success. Changing climate would drive populations of cane toads out of areas by making conditions unfavorable. However, limiting immigration and increasing emigration sounds easier than it is – there is difficultly for humans to accomplish desired environmental change, especially without harmful consequences.

population as a Unit of Study A population is the primary focus of ecologists because it is the unit of study of ecology and evolution. An individual is not as important in studying trends associated with changes in gene flow and in the environment. While a single person may respond one way to a changing factor, such as increased sunlight, her or his reaction is not so import- ant to ecologists. If a person moves to Florida and becomes tanned, possibly dying from skin cancer after 30 years of exposure, an ecologist cannot make strong ecological con- clusions. A single data point cannot drive research findings. If, however, offspring of

Population ecology

The study of a population of organisms and how it interacts with its environment.

Population growth

The increase in the number of individuals inhabiting a place.

Population size

A measurement of population that gives the raw number of organisms in a population.

Population density

A measurement of population that reveals the number of organisms per area of land in an ecosystem.

Immigrants

New organisms moving in from other areas.

Emigrants

Organisms leaving an area.

Demographics

The data collected by ecologists about the statistics of a population of species.

Births

New born additions.

Deaths

The end of life; those leaving permanently.

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populations who move to Florida die off more rapidly as a group 30 years after their emi- gration, ecologists can draw stronger conclusions about environmental effects. Groups of organisms (populations) are studied in ecology to make generalizations.

Population demographics are not measurements of an individual: births, deaths, immigration, and emigration are all population terms. They are used to view how whole groups change and form patterns within ecosystems. Ecology requires that ecologists are both inductive and deductive, terms that harken back from Chapter 1. These are each methods of finding the answers to scientific questions. Ecologists make predictions and form models based on information obtained from their measurements of groups. Ecol- ogy forms hypotheses to test about certain questions in deduction: a study introducing sterile males into a population of cane toads, for example. Induction looks at the many factors about cane toads – their toxins, fertility, and relationships with other organisms – to form ideas on how to solve the toad infestation. To illustrate, perhaps a genetically modified hardy reptile could increase B. marinus death rates. Our story would then have a happier ending. There are many ecological approaches that could be taken. Both induc- tion and deduction are vital in studying population ecology.

Individuals were the focus of the previous unit in this text, on anatomy and phys- iology. It studied the individual and its components: the parts of the digestive system, the function of the liver, and the ways the heart works and malfunctions. It studied the organism down. However, ecology is a type of macrobiology, which studies the organism up. It looks at the organization of populations. It shows the movement of genes through a population and not simply the genes of an individual. The ways populations form patterns in their arrangement and the responses to other organisms and nonliving factors are an ecologist’s field. The chapters in this unit represent a shift from micro- to macrobiology.

population Growth As described in Chapter 1, populations tend to increase in size and overreproduce, unless checked by predators. Charles Darwin, in Chapter 1, describes population expansion as a driving force in evolution, as you may recall. Populations grow too large, and competi- tion for scarce resources leads to a survival of those best adapted. Populations grow until they exhaust their available resources.

An exponential model of population growth depicts a population increase that is unlimited. This model assumes that there are no predators, unlimited resources, and no pathogens. A population will grow, under these conditions, to its biotic potential or maximum possible growth under ideal conditions. Population increases for B. marinus in Australia have reached almost its biotic potential. Our story shows, like the cane toad, many invasive species often grow unchecked by predators. They enjoy conditions of full resource availability. Their growth is exponential (Figure 17.2a) and continues until changing conditions limit them.

Populations can never continue to grow unchecked. Even prokaryotes, which grow at the biotic potential most of their lives, become checked with changing environmental con- ditions and competition between themselves. The main limiting factor to population growth in cane toads is one another. When some cane toads are killed by human methods, it stim- ulates even more growth because the competition diminishes between toads themselves.

In natural ecosystems, populations are limited by a scarcity in resources. This results in a logistic model of population growth. In this model, a population first grows slowly, during a lag period, as population gains in size and colonizes an area (Figure 17.2b). Then, a time of rapid and unchecked growth, called the exponential period, occurs when resources are unlimited and the numbers in the population explode exponen- tially. After this phase, growth slows as limiting factors, such as food, spaces, light, and water, become scarcer. These are called density-dependent factors because they become

Logistic model of population growth

A model that depicts the decrease of population growth rate with the increasing number of individuals.

Exponential period

A time of rapid and unchecked growth.

Density-dependent factors

Factors that limit the population size, whose effects are dependent on the number of individuals of a population.

Exponential model of population growth

A model that depicts the increase of population growth at a constant rate.

Biotic potential

Maximum possible growth achieved by organisms under ideal conditions.

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limiting only after populations reach higher densities. This period continues till a popu- lation reaches its carrying capacity or K, defined as the maximum number of individuals an environment is able to sustain in the long term. Most organisms follow this pattern of growth over time. When deer are introduced into a new area, they increase and level off in their rates of growth in a logistic pattern. The logistic model of population growth appears as an S-shape. Figure 17.2b shows this pattern for deer populations in Australia.

Human population Structure Human population has surpassed 7 billion people and is expected to reach 9 billion by 2050. Each year, 80 million new people are added to the total world population, with birth rates higher than death rates (Figure 17.3). During the past 1,000 years, human world population expanded exponentially. Most ecologists predict the emergence of logistic S-shaped growth in the 21st century.

Carrying capacity (K)

The maximum number of individuals an environment is able to sustain in the long term.

Figure 17.2 a. Exponential growth of B. marinus (cane toad). The cane toad population has expanded since 1935 without natural predators. Bacterial growth data, in the chart above, mirror an exponential pattern of growth. b. Logistic model of growth for deer, normally kept in check by limited resources and predators, shows an S-shaped curve of growth. Deer are usually kept in check by many factors including predators. From Biological Perspectives, 3rd ed by BSCS.

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Figure 17.3 Human population growth. World population grew rapidly since the outbreaks of the plague in Europe and Asia. Humans are experiencing exponential population growth today. From Biological Perspec- tives, 3rd ed by BSCS.

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Studying the age structure of a population depicts the number of individuals at dif- ferent age groups. Age structure diagrams are used to predict future patterns of growth or declines, shown in Figure 17.4. The age structure of developing nations is pyramid in shape, showing that there are many more young than old. This indicates that the population is growing. In developing nations, the age structure diagram is rectangular, with individuals evenly distributed at each age level. This indicates that populations in developing nations are stable. Age structure diagrams help us to predict rates of growth for populations.

Of course, number of children actually being born is an important factor in predict- ing population growth. Fertility rate is defined as the average number of children born to females in a population. The world fertility rate declined from 6.5 children per mother in 1950 to 2.5 today. The declines in fertility rate, due to education programs, contra- ception access, and other methods, have slowed the world population growth. However, fertility rate is still above the replacement level of 2.1. Only China, with rates around 1.6, will experience population decreases due to their one child per couple policy.

Age structure diagram

A graphical illustration that are used to predict future patterns of growth or declines of various age groups in a population.

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Figure 17.4 Age structure diagrams: developing and industrialized nations. Devel- oping nations show a greater proportion of younger people and thus are predicted to have higher rates of growth.

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The growth curve for past and current world population is shown in Figure 17.3, a result of the effect of high fertility rates in the world.

In 1996, the US population was 235 million. At the time, it was estimated that the carrying capacity of the United States was 250 million people. Today, we have over 310 million people, overshooting carrying-capacity estimates. Were the original estimates wrong? Were ecologists just naysays?

Factors changed, which could not be predicted at the time, which enlarged the United States carrying capacity substantially. There have been significant advances in farming and improvements in production and preservation of foods. The use of genetically mod- ified organisms to increase food supplies, expansion into new habitats to obtain new resources, and new crop methods has increased our carrying capacity to 500 million, according to some estimates.

The US population grows each year by 3.3 million people, making us the fastest growing industrialized nation in the world, according to the US Census Data. The US population, given current rates and density-dependent factors, will reach 500 million in 2050. With new estimates of a carrying capacity, ecologists fear the effects of reaching these levels. Resource limitations are eventually expected to limit population growth. Of course, the wealthiest people consume most of the world’s resources (Figure 17.5).

In every population, starvation, disease, and violence are the results of reaching carry- ing capacity. On the other hand, Often, density-independent factors decrease populations. These are the factors that increase death rate regardless of density. Landslide, earthquakes, and floods destroy life by directly killing organisms or reducing the size of their resources.

Both density-independent and density-dependent factors interact to affect popula- tion size. It is likely that cane toad populations will experience diseases, new predators, and natural disasters such as desertification, given enough time. If the numbers of toads increase, there are more chances for transmission of viruses and parasites. With greater density, disease is shown to spread more quickly. A population’s increase is also seeds of its own destruction – for humans as well as cane toads.

A population’s use of resources determines how quickly it will reach the carrying capacity. The ecological footprint of an organism or a population is defined as the amount of resources used: land, fuel, water, food, and other items. Some nations such as Sweden and New Zealand have small ecological footprints, while the others like the United States, Japan, and England have large ones. The ecological footprint of an American is 24 acres

Density- independent factors

Factors that limit population size, whose effects do not depend on the number of individuals of a population.

Figure 17.5 The wealthiest people in the world use more resources than others. The wealthiest 16% in the world consume 80% of the world’s resources. The cartoon depicts the United States as overusing the world’s energy resources.

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Ecological footprint

A population is defined as the amount of resources used.

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worth of resources, but one from an Egyptian is 4 acres and Bangladesh is 1.5. The map in Figure 17.6 gives a visualization for our resource use on the planet.

The United States, for example, represents only 5% of the world’s population, but consumes 30% of the world’s natural resources. The richest 16% of people consume 80% of the world’s resources. This disparity between nations and the unsustainable lev- els of resource management have dire long-term predictions.

However, some ecologists and economists have a more positive outlook. They surmise that the carrying capacity can forever be increased by human innovation, as done in the past. As cited earlier in this section, this positive argument relies on the power of the human mind to solve the population explosion issue. Possible solutions include harvesting ocean algae, mass producing farm fish, and reducing population on Earth by traveling to Mars and the moon. All of these are plausible, but each possibility is only extrapolation at this time.

Figure 17.6 Our ecological footprint varies for each nation in the world. The eco- logical footprint of an American is 24 acres worth of resources, but an ecological foot- print from an Egyptian is 4 acres and from Bangladeshi 1.5 acres.

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“Once it was necessary that the people should multiply and be fruitful if the race was to survive. But now to preserve the race it is necessary that people hold back the power of propagation,” by Helen Keller, deaf and blind author and lecturer.

Survivorship Curves and Life History Strategies The life history of organisms in a population is the set of inherited characteristics of an individual that tell us how it lives. An organism’s lif e history, also called its life strategy, includes its fertility rate, breeding patterns, life span, and age at first reproduction.

There are two types of life histories, each representing opposite ends of a spectrum. The first type, used by dandelions and flies, is termed an opportunistic life history. It is also called an r-selected strategy. In this method of living, there are large numbers of young per breeding event, very little or no care of the young, shorter periods of devel- opment, and a higher mortality in early life. Usually, those organisms with opportunistic life histories live a short time and cannot care for their young. Their strategy is to have as many offspring as possible, putting their success in quantity of children and not quality of caring for them. Most flies live only a few weeks. This means that a successful life

Life history

Series of changes an organism undergoes during its lifetime.

Opportunistic life history, r-selected strategy

type of life history when parents have many young and invest very little in each.

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history does not include a long life raising young. It instead focuses on rapid develop- ment of young to adulthood so they do not need care. The cane toads in our story had an opportunistic life history, putting little effort into raising young. Opportunistic organ- isms often exhibit population booms like the one depicted in our opening story.

The second type of life history, called an equilibrial life history, occurs when parents invest in extended care to their young, live a long time, and have few offspring. It is also called a K-selected strategy. Their efforts go into quality of care and not quantity of young. Organisms such as elephants, coconut palm, and humans exhibit an equilibrial life history. They have few offspring and invest heavily in each. A whale and human usually produce only one newborn at a time. A coconut palm waits a long period of time before producing limited numbers of coconuts.

The two life history types are given in Figure 17.7. Each species evolved a particular life history to optimize the survival of its mem-

bers. While there are maximum life spans in every species, not all species will reach this age. In humans, the oldest documented case was Jeanne Calment, who lived up to the age of 122 years, 164 days. Our life history is K-selected and we have longevity, on average long exceeding the time needed to care for our young. However, humans are limited by genetics and may live for only so long.

Equilibrial life history, K-selected strategy

A type of life history that occurs when parents invest in extended care to their young, live a long time and have few offspring.

Figure 17.7 Opportunistic and equilibrial life histories. a. r-selected species such as quinoa produce many tiny seeds in one growing season. b. The coconut palm grows slowly and produces few seeds in its entire lifetime.

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A SuPErCEntEnArIAn LIvES FOr122 YEArS . . .

Jeanne Calment was born in Aries, France, on February 21, 1875. She is the oldest centenarian in history, dying at age 122 in 1997. Longevity ran in her family: her mother died at age 86 and her father died at age 94. These were very old ages in the 1800s, when medical treatments were limited.

She married her cousin but he died of food poisoning in 1942 at age 47. They had only one daughter who died of pneumonia in 1934. She then raised her grandson who died in 1963 from injuries in a car accident. Jeanne never worked a job and attributed her long life to not letting herself get stressed and to eating a diet rich in olives.

Did Jeanne Calment take care of her health? She smoked until age 119 and ate two pounds of chocolate every week. She rode her bicycle until age 100 and although going blind and hard of hearing in her last few years, she remained

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The maximum lifespan in humans is between 100 and 120 years. Jeanne Calment is an extreme example of survivorship. Human life expectancy is the age at which 50% of people in one’s age group have died. To illustrate, life expectancy for men in the United States is 78 years. This means that by age 78 a man has lost half of his cohorts. Life expectancy for women is 82 years. A survivorship curve plots the number of survivors in a population over time.

Ecologists have classified three types of survivorship curves. Type I curves show most individuals surviving until the end of life, when death occurs in high proportions. Humans and large animals, which carry out equilibrial life histories, exhibit this type

Survivorship curve

A graph that gives number of survivors in a population over time.

mentally alert and capable. She appeared humorous: When asked on her 120th birthday what kind of future she expected, she answered, “A very short one.” and on her 110th birthday, she commented, “I’ve waited 110 years to be famous. I count on taking advantage of it. Why did Jeanne Calment live for so long . . .?

Figure 17.8 Three types of survivorship curves show the numbers of individuals surviving throughout their lifespans.

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of survivorship curve. Most individuals live long enough to care for their young. Equal rates of death at every age occur in Type II survivorship curves. This distribution is seen in organisms, such as those in the wild, lizards, birds, and small mammals, which have equal chances at predation and environmental dangers at all ages. Those with Type III curves die off very early in life, depicted by an inward bulge in the graph. Organisms with a Type III curve include frogs and marine animals that give off large numbers of fertilized eggs into the wild. There is a high chance of death due to environmental dan- gers, as the eggs are defenseless and unprotected. Figure 17.8 depicts the three types of survivorship curves.

Characteristics of Communities roles The second part of this chapter explores the features of a community. It examines the interactions of organisms within a community of populations. A forest, with maple trees and white pines, reptiles, amphibians, and humans constitute a community. It is a set of different populations living together. A community may also be something unseen – such as the microbiome of bacteria residing on your skin – which contain millions of species not visible to humans (Figure 17.9).

A biological community therefore includes all of the populations of organisms liv- ing in an area at a particular time, and their relationships with each other. The role an organism plays in the community is it ecological niche. Its niche displays how an organ- ism interacts with all of the features of its environment. The space an organism occupies, including all of the factors with which an organism interacts, is known as its habitat. A habitat is the area in which an organism lives. Some factors in a habitat are nonliving, called abiotic factors. These include soil, sunlight, temperature, and rainfall. Other fac- tors comprise the living things, called biotic factors. These include plants, animals, and microorganisms. Organisms use both biotic and abiotic factors to interact with other members of the community and the environment.

An organism’s ecological niche may be limited by the resources it is actually able to use. An organism’s fundamental niche is the area and resources that it is theoretically able to utilize. Its realized niche is the area and resources actually able to be used by a population. Consider the barnacles on the Scottish seacoast, as an example. They consist

Ecological niche

The role an organism plays in its environment.

Habitat

The space an organism occupies, including all of the factors with which an organism interacts.

Abiotic factors

The non-living factors in a habitat.

Biotic factors

Factors that comprise the living things in a habitat.

Fundamental niche

The area and resources that an organism is theoretically able to utilize.

realized niche

The area and resources that an organism is actually able to use.

Figure 17.9 Communities come in big and small sizes. a. Forest community. b. Microbiome community taken from human skin.

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of two different genera: the Balanus is best adapted to exploit resources at lower portions of the coast and the Chthamalus genus is better suited for upper parts of the shore (Fig- ure 17.10).

interactions within Communities Competition In the example above, the fundamental niche of both genera of barnacles is the entire Scottish coast. Under ideal conditions, with the other genera not around, each are able to use resources in the upper and lower regions of the coast. However, in reality, their real- ized niches matter more. Realized niches are exploited because of competition between the two genera of barnacles.

Competition occurs when organisms strive for the same limited resource. Competi- tion reduces the survival of both organisms. They spend their energy competing with one another. Russian scientist G.F. Gause, in the 1930s developed the competitive exclusion principle, which states that organisms will compete with each other in an area until one goes extinct. He studied two species of paramecium, P. caudatum and P. aurelia. When grown separately in test tubes, each species thrived, using resources. When grown in the same test tube, P. aurelia drove P. caudatum into extinction (Figure 17.11).

Species do evolve to coexist with each other. All birds consume berries, but different species are adapted for different sizes, shapes, and types of berries. Competition does not always need to cause species extinction in an area. When two competitors coexist

Competition

The activity that occurs when organisms strive for the same limited resources.

Competitive exclu- sion principle

A principle, which states that organisms will compete with each other in an area until one goes extinct.

Figure 17.11 Competitive exclusion principle: graph of P. caudatum and P. aurelia

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in the same area, they use resources in different ways, in a process known as resource partitioning. Resources are subdivided into different categories, and each category is separately used by competitors.

Resource partitioning is often accomplished by character displacement. In charac- ter displacement, organisms evolve characteristics to help them to partition resources. Sometimes new traits cause partitioning based on location, as described in our exam- ples of barnacles in Scotland. Sometimes different resource use is temporal, or based on time of the day spent in a habitat. Bats, for example, hunt for prey at night, limiting their competition with birds, as well as predators. Regardless, resource partitioning is a mechanism by which competition is reduced between organisms.

When competition occurs between two different species, it is known as interspecific competition. If B. marinus, the cane toad outcompetes Rana pipiens, the North Ameri- can frog, in obtaining a fly meal, it is an example of interspecific competition. This is the most common form of competition in community ecology. When organisms of the same species compete with each other, it is called intraspecific competition. Mate competi- tions between two deer or when two hemlock trees struggle for limited light and water represent intraspecific competition.

predator–prey relationships Nature can appear cruel to human society. A fast cheetah stalks and kills a cute, little fawn. A California King snake, Lampropeltis getula, swallows a mouse whole, seem- ingly without mercy. We feel sorry for the creature that we like – the one which loses. However, this relationship between species in a community is vital.

The connection between the two organisms is called the predator-prey relationship. Predation is essential for energy flow and the survival of many species in a community. Predation occurs when an organism of one species – the predator – stalks and kills an organism of another species – the prey. Predators obtain required energy from the parts of its prey. When L. getula stalks a mouse, for example, it has adapted, over millions of years of evolution as shown in Chapter 10, strategies and structures to consume small animals. The answer to the problem in our story is to find a predator that is able to withstand the toxin of the cane toad. It kills crocodiles and freshwater turtles when they eat them. There are many species that prey successfully on the cane toad but they

Figure 17.12 A corn snake is a predator that swallows its prey whole. This corn snake is eating a mouse.

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The connection between two organisms of unlike species.

Predation

When one organism stalks and kills an organism of another species.

Intraspecific competition

The competition between organisms of the same species.

resource partitioning

The condition where two competitors coexist in the same area and use resources in different ways.

Character displacement

The phenomenon where organisms evolve characteristics to help them to partition resources.

Interspecific competition

The competition between two different species.

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are not native to Australia. Ecologists are searching for a suitable predator for the cane toad. However, they should be careful not to introduce a new invasive species. Snakes are an excellent predators to rodents (Figure 17.12), but most snake species cannot eat the cane toad.

The most notable predator–prey relationship takes place between the lynx and the hare. The lynx, a predator in Figure 17.13, stalks and kills its prey, a snowshoe hare. Lynx and hare populations fluctuate, dependent in part on one another. When plot- ting the frequency of individuals of each population over time, Figure 17.13 shows the changes that occur for each species in tandem with one other. As the lynx preys on the hare population, lynx increase because they are exploiting the resource. Then, as they use up the hare (hare population declines) as a food source, they too experience pop- ulation decreases. With fewer lynx, more rabbits survive. Fewer lynx predators allow their numbers to thrive. Afterward, the lynx again have more food available from the increase in hare population. This fluctuation in frequencies make the predator and the prey dependent on each other.

Defenses Evolve However dependent, prey always lose because they are killed and eaten by the predators. The prey’s reproductive success is reduced in its interactions with predators. Therefore over time, many prey species evolved a series of defenses to combat predators. Quills on a porcupine or poisonous glands in a cane toad repel predators and save a prey’s life. There are several defense mechanisms used by prey. They are divided into two types: those that constitute physical prey defenses such as chemicals and structures; and those that are behavioral prey defenses, which comprise the actions a prey takes to ward off predators.

At the same time, predators have evolved counter-measures to prey. They have devel- oped (and continue to evolve) structures and strategies that combat changes in prey. It is a coevolutionary arms race between the two. As discussed in Chapter 9, the ongoing coevolution of the Passiflora flower and the Heliconius butterfly represents an arms race in defenses. In some cases, organisms evolved to help each other to defend against mutual enemies. Several species of ants become attracted to substances on conifers. Ants on coni- fers defend against other insects that eat the tree’s needles. The conifers provide a defense against predators for ants. Together, they evolved strategies to help each other defend against predation. Let’s explore the prey defenses that developed across other species.

Figure 17.13 Predation. The lynx, a predator, stalks and kills its prey, a snowshoe hare; graph of population change of lynx and hare

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physical prey Defenses Mechanical defenses Mechanical defenses are structures, such as quills on porcupines or shells surrounding a turtle, which serve as passive defenses against predators. They require no work and no confrontation to deter predation. A turtle shell is tough and prevents the soft-bodied turtle from many deadly encounters.

Camouflage Armored shells of turtles also usually blend in with the environment. When organisms become less visible in their environments, they are said to use camouflage to avoid being seen. The walking stick, an insect that resembles a branch on a plant, easily blends in with its surroundings. This structure allows a passive defense for walking sticks, as depicted in Figure 17.14.

Warning Coloration Often a bright-colored organism indicates that it is poisonous. The azure poison dart frog, for example, is orange and spotted to warn predators to beware. Warning coloration is called aposematic coloration and serves to deter predators. However, the poison-color

Aposematic coloration

Warning coloration that serves to deter predators.

Figure 17.14 Physical prey defenses. a. Turtle in a shell. b. Aposematic coloration of azure poison dart frog. c. Viceroy and Monarch butterfly. d. A walking sick Diapheromera fermorata.

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The act by which organisms become less visible in their environments to avoid being seen.

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link is not necessarily always present. The cane toad, B. marinus, in our story is drab, but still poisonous. Plants from the noncolorful genus Strychnos produce the toxin strych- nine that kills many vertebrates.

When a palatable species capitalize on aposematic coloration, it mimics the poison- ous organism. This is called mimicry. For example, the Monarch butterfly is poisonous to mammals and bird, containing a toxin that affects heart rate. The Viceroy butterfly resembles the Monarch, both featuring similar orange–black patterns and get protection by appearing similar (Figure 17.14c).

Behavioral prey Defenses Group Behavior The way an organism responds to stimuli or acts comprises their behavioral defenses (Figure 17.15). There are both passive and active forms of behavioral prey defenses. By traveling in groups, prey reduce their individual risks. Usually, when a predator enters the scene, some prey respond, giving warning to the other to flee. In another way, the large numbers of cane toads, for example, satisfy a predator’s appetite and allow oth- ers to go unharmed. Group behavior is a passive adaptation to predation (Figure 17.15 c and d). It saves many by sacrificing the few. In Chapter 20, we will explore how the genetic predisposition to group thinking influences societal behaviors.

Alarm Call Sometimes in a group, there is an alarm call, which is signaled by one member, that a predator has been spotted. An owl may howl or a bird may chirp in an alarm call. This enables the other members of the group to hide and flee or to fight back.

The first is a passive defense, and many animals adapt this strategy when encounter- ing humans, for example. Cattle will travel in herds, fish in schools, and birds in a flock. Often, mainland animals, as opposed to island ones, adapt a passive retreat defense from humans. On the island in our story, hiding and fleeing, in fact any fear from humans is absent in cane toads. These organisms did not evolve the behavior against humans because on islands their species never encountered humans until recently. The second strategy is an active defense. When organisms fight back, they use their defenses to ward off predators. As we discussed in Chapter 10, ostriches are flightless but have strong wings to beat back the predators, when they are unable to run away (Figure 17.15b).

Mimicry

The resemblance of one organism to another

Group behavior

A passive adaptation technique to predation.

Alarm call

A warning signal made by an animal or bird about a predator or when startled.

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Sometimes a behavioral defense will be active to a point of suicide. For example, often an enemy insect group attacks a colony of the Malaysian exploding ant, Campono- tus saundersi. C. saundersi soldiers march up to the enemy. In line and in unison, the C. saundersi ants contract poison glands in their abdomens, squirting formic acid onto the predators.

In the process, C. saundersi soldiers die, with their abdomens exploding. It is an example of devotion to the colony, as suicide ants lose their lives to protect against predators. We will explore the role of genetics in forming social systems in organisms further in Chapter 20.

plants and Herbivory Have you ever looked at the leaves on a tree in early spring compared with the late sum- mer or fall? Early in the growing season, leaves are fresh and undisturbed, but by the end of the season, they change. They become filled with holes, laden with fungus growths, and ultimately appear ugly. The changes are due to herbivory, or the consumption of plants and plant parts by other organisms. In herbivory, the plant may or may not die as a result. Herbivory is commonly thought of as cattle grazing on grasses; but other organisms, such as fungi and bacteria, feed on plants. Herbivory is a form of predation and it kills many plants.

Some plants evolved defenses against herbivory. Humans are unable to eat most forms of grasses because they contain silica, making hardened blades. These plants are too tough

Herbivory

The consumption of plants and plant parts by other organisms.

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Figure 17.15 Behavioral prey defenses. a. Red carpenter ant attacks a gnat. b. Ostrich will use its wings to protect her eggs. c. Cattle in herds. d. A flock of pigeons.

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for humans and many animals to consume. Some organisms, such as the shrub oak, evolved its defense by having most of its mass underground in the form of roots. This way, even if herbivores devour the plant, most of its energy is underground and ready to resprout. The best known evolved defense against herbivory, however is the poison from the poison ivy plant, Toxicodendron radicans. It contains a toxin that binds to T-helper cells. As you may recall from Chapter 14, T-helper cells begin the specific immune response. When the toxins of T. radicans combines with T-helper cells, they initiate an allergic reaction. These manifest as skin rashes commonly seen after contact with poison ivy (Figure 17.16).

Symbiosis Many relationships within communities form close bonds, making them interdepen- dent. Many organisms live in close, intimate association forming a relationship called symbiosis.

There are three types of symbiosis:

1) Commensalism, which occurs when one organism benefits and the other is unharmed by the relationship (Figure 17.17). When epiphytes or vine-like plants grow on trees, they do not harm the supporting plant but do not help it either. Instead, the epiphyte’s motive is to gain height and obtain its limiting resource – sunlight. They are stealing a spot on the tree but not giving anything back. In animals, barnacles are small marine creatures that latch onto skin. When they adhere to a whale’s skin, they are hitchhikers and gain a “free ride” on the whale. The whale receives nothing in return for the trip but is not harmed as the weight of the barnacle is negligible.

2) Mutualism occurs when both organisms benefit in a relationship. Mutualism is commonly found in nature. Both organisms have a stake in the association, making it a stable strategy for survival. In the Alder tree, a special type of bac- teria (which will be discussed in Chapter 19) called nitrogen-fixing bacteria live in the root nodules of the tree. The nodule of the tree provides protection in a “home” for the bacteria. The bacteria provide accessible nitrogen for the Alder tree. Without nitrogen from the bacteria, most of it is unavailable to the tree because it is a gas. Other forms of mutualism are closer to home. The bacteria in our large intestines, described in Chapter 12, provide us with vitamin K and our colons provide a safe and anaerobic home for the enteric bacteria. Mutualism has numerous examples in nature.

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Figure 17.16 a. Toxicodendron radicans. b. A rash on a human from poison ivy.

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Symbiosis

A relationship formed between two different organisms living in a close, intimate association.

Mutualism

A relationship in which both organisms benefit.

Commensalism

The type of symbiosis which occurs when one organism benefits and the other is unharmed by the relationship.

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3) Parasitism is the symbiotic relationship in which one organism benefits and the other is harmed. Parasites kill more people than by predators or by compe- tition. As discussed in Chapter 5, roughly 1 million people die each year from the malaria parasite, Plasmodium alone; and yet only a handful are attacked by sharks. The contrast shows that organisms unseen have more impact on human society that we often realize.

Parasites in the animal phylum Nematode (discussed in Chapter 10), for example, the hookworm, Ancylostoma duodenale, lives in human intestines and survives on blood (Figure 17.18). However, parasitism, as by a hookworm, is different from predation. Parasitism does not seek to kill its host, merely weakening it as it drains away the host’s resources. Predation always seeks to kill its prey. If the parasite kills its host, it too dies, so it pays for the parasite to prevent too much abuse of its host. Many times though, and eventually, parasitism does kill a host organism.

Figure 17.17 Commensalism: Spanish moss on a tree to capture sunlight. While the tree obtains no benefits, the moss species is able to get greater access to sunlight and therefore food.

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Figure 17.18 The hookworm, Ancylostoma duodenale, is a parasite in the intestines of humans.

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Fungi are the ultimate parasites that evolved to lose their own chlorophyll and leaves. They live off the dead, as described in Chapter 8, and cannot make their own food. Fungi evolved a strategy to completely rely, as a parasite, on other organisms.

Other forms of parasitism occur in nature. Brood parasitism takes place when a bird species lays eggs in another bird’s nest (Figure 17.19). The foreign eggs then hatch and are raised by the host mother. The real mother avoids the costs of rearing her young. It is a form of stealing because it saps the energy from the host mother. In cowbirds, females can lay up to 30 eggs a season because they are free of parental care for these newborns. It is a successful parasitic strategy that improves the reproductive success of cowbirds.

Some parasitoids take parasitism to new levels. They lay their eggs within other species. When these eggs hatch, they eat the host organism from the inside out, using it for developmental energy. The braconid wasp, Cotesia congregatus, for example, uses an ovipositor (long tube) to lays its eggs within the body of the tomato horn- worm (Figure 17.20). When wasp eggs hatch within the hornworm, they gnaw at the

Brood parasitism

A form of social parasitism in which a bird species lays eggs in another bird’s nest.

Figure 17.19 Brood parasitism: Chestnut-headed oropendolas (Psarocolius wagleri) suffer brood parasitism by giant cowbirds (Molothrus oryzivorus).

Figure 17.20 The braconid wasp, C. congregatus, uses an ovipositor to lay its eggs within the body of the tomato hornworm. The eggs of the wasp hatch and eat the tomato hornworm (shown in figure above).

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Parasitoid

An organism living that spends some period of its development on or in a host organism and later kills its host.

Parasitism

The symbiotic relationship in which one organism benefits and the other is harmed.

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caterpillar hornworm until they reach its exterior. The wasp eggs devour their host completely and emerge as adults from a dead caterpillar carcass.

The many community interactions presented in this section should be understood as complex and sometimes overlapping (Figure 17.21). While mutualism may occur, for example, between species, another interaction is usually taking place simultaneously. A braconid wasp may have within it a parasitoid living in its internal cavities. It is esti- mated that 25% of insect species are parasitoids, forming many interactions within their communities.

Figure 17.21 Multiple relationships in a community: arrows depict relationships between populations within a river community in the waters below these boaters. From Biological Perspectives, 3rd ed by BSCS.

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Summary Invasive species take over regions in which they lack natural predators and have abun- dant resources. There are over 1,500 known invasive species adversely affecting regions around the world. Ecologists study these regions by analyzing population demograph- ics and by looking at how populations interact within a community. Populations grow depending upon the conditions to which they are adapted in their environments. They are limited in growth by scarcity of resources in a given area. We can predict future growth of populations based on their age structure, life history, fertility rates, and sur- vivorship curves. Organisms play differing roles within their community. Many kinds of interactions result from this including competition, predator–prey, and types of symbiosis.

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Summary: key points

• Invasive species, without natural predators, grow logistically and exhaust resources for other species in a community.

• Most populations grow at first exponentially and are then limited by a scarcity in resources at an ecosystem’s carrying capacity.

• An opportunistic life history capitalizes on high numbers of offspring, and an equilibrial life history emphasizes care of the young.

• Organisms in a community have a niche, which may be fundamental or realized. • Interactions within a community include the antagonistic, such as competition and predation and

parasitism; and the cooperative, such a mutualism and, to a lesser extent, commensalism.

abiotic factors age structure diagram alarm call aposematic coloration biosphere biotic factors biotic potential births brood parasitism camouflage carrying capacity, K character displacement commensalism community competition

competitive exclusion principle deaths demographics density-dependent factors density-independent factors ecological footprint ecological niche ecology ecosystem emigrants equilibrial life history, K-selected strategy exponential exponential model of population growth fertility rate

KEY tErMS

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fundamental niche group behavior habitat herbivory immigrants interspecific competition intraspecific competition life history logistic model of population growth mimicry mutualism opportunistic life history, r-selected strategy

parasitism parasitoid population population density population ecology population growth population size predation predator–prey relationship realized niche resource partitioning survivorship curve symbiosis

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Multiple Choice Questions

reflection questions:

1. The cane toad grows: a. inversely b. exponentially c. diversely d. proportionally

2. Populations are: a. groups of communities b. smaller than groups c. larger than ecosystems d. the unit of study in ecology

3 When a population of squirrels hits its _________, it shows a ____ growth curve. a. exponent; exponential b. exponent; logistic c. carrying capacity; exponential d. carrying capacity; logistic

4. A population of field mice has a chance of death equal at all of their ages, with predation a steady possibility. Their survivorship curve would appear as Type: a. I b. II c. III d. IV

5. Before humans hit their carrying capacity, they are likely to experience: a. violence b. disease c. starvation d. growth

6. Which represents a logical order, in the development of new niches for organisms in a high population density and resource scarcity? a. Competition ➔ resource partitioning ➔ character displacement b. Competition ➔ character displacement ➔ resource partitioning c. Character displacement ➔ resource partitioning ➔ competition d. Resource partitioning ➔ character displacement ➔ competition

7. Which is an example of an abiotic factor in a forest community? a. Squirrel droppings b. Sunlight levels c. Competition between wolves d. Competition between wolves and dogs

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8. Which takes place when both organisms benefit in a relationship? a. Mutualism b. Commensalism c. Predation d. Parasitism

9. Which correctly MATCHES terms in community ecology? a. Predator – mutualism b. Herbivory – competition c. Parasite – commensalism d. Predator – prey

10. Herbivory is a form of: a. predation b. mutualism c. commensalism d. all of the above

Short Answers

1. Invasive species are exotic to new areas and growth rapidly. Give two reasons why an invasive species is able to take advantage of a new area.

2. Define the following terms: population size and population density. List one way each of the terms that differ from each other in relation to their: a. importance in predicting competition in a population; b. importance in predicting resource use in an area; and c. relationship with each other.

3. Some ecologists argue that “there is no true form of commensalism.” Define com- mensalism and give an example of it in nature. Do you agree with this statement? Defend your argument.

4. Draw a sketch of an age structure diagram in a growing population. Give an exam- ple of a nation with this type of age structure diagram. What does a high fertility rate tell you about the future of this population?

5. Explain the difference between a fundamental niche and a realized niche.

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6. How does competitive exclusion result in: a. character displacement and b. extinc- tion? Describe the pathway that a community takes to lead to each result.

7. Define aposematic coloration. Give an example of this in nature.

8. For question #7, how does mimicry act as a physical prey defense? Give an example in nature.

9. Describe the predator–prey relationship. Does it pay for the predator to kill its prey? Does it pay for predators to kill off its prey population?

10. Define brood parasitism and parasitoids. How are the two types of parasitism simi- lar? How are they different? Give an example of each.

Biology and Society Corner: Discussion Questions 1. In the past 25 years, China has implemented a One Child Policy, which restricts

couples by placing sanctions on them for having more than one child. However, it is now allowing two children per couple. What changes have taken place societally in China as a result of this policy? What do you recommend for solutions? What do you predict for future generations, as Chinese society favors sons?

2. In the story, the cane toad was introduced into Australia in 1935 to combat beetles. Beetles destroy crops and thus the food supply. The scientists who introduced the cane frog argued that at least their methods were natural, unlike methods of animal control used today. Do you agree or disagree with these scientists? Explain your answer.

3. To reduce our ecological footprint, some scientists argue that the United States would see a reduction in its standard of living. Our resource use is the highest in the world, at this time. Would you be willing to lower your standard of living to reduce our ecological footprint? Why or why not?

4. Unsustainable human population growth is an environmental threat. However, two scholars argue about the effects of human population growth. Julian Simon, an econ- omist, contended that human innovation and technological advance will increase the carrying capacity. Paul Ehrlich argued against Simon, citing limited resources and predicted logistic growth curves for humans. Research these two opposing sets of viewpoints. On the basis of your research, which side do you take? Why?

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5. Jeanne Calment lived for 122 years. Would you like to live for that long? How long would you want to live? What factors play a role in your decision making?

Figure – Concept map of Chapter 17 big ideas

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