APES Chapter 4 Biodiversity and Evolution PDF

4 Biodiversity and Evolution Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook an...

4 Biodiversity and Evolution Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Few problems are less recognized, but more important than, the accelerating disappearance of the earth’s biological resources. In pushing other species to extinction, humanity is busy sawing off the limb on which it is perched. PAUL EHRLICH Key Questions 4-1 What is biodiversity and why is it important? 4-2 How does the earth’s life change over time? 4-3 How do geological processes and climate change affect evolution? 4-4 How do speciation, extinction, and human activities affect biodiversity? 4-5 What is species diversity and why is it important? 4-6 What roles do species play in ecosystems? Monarch butterfly on a flower. Ariel Bravy/Shutterstock.com 77 Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. CORE CASE STUDY Why Are Amphibians Vanishing? Amphibians—frogs, toads, and salaman- world have declined or vanished (Figure sensitive biological indicators of changes in ders—were among the earliest vertebrates 4-1). According to the International Union environmental conditions such as habitat (animals with backbones) to emerge from for Conservation of Nature (IUCN), about loss, air and water pollution, ultraviolet the earth’s waters and live on the land. 33% of all known amphibian species are (UV) radiation, and climate change. The Historically, they have been able to adjust threatened with extinction, and more than growing threats to their survival indicate to and survive environmental changes 40% of all known amphibian species are that environmental conditions are deterio- more effectively than many other species. declining. rating in many parts of the world. However, the amphibian world is changing No single cause has been identified to Second, adult amphibians play impor- rapidly. explain the declines of many amphibian tant ecological roles in biological com- An amphibian lives part of its life in species. However, scientists have identified munities. For example, amphibians eat water and part on land. Now, many of the a number of factors that affect amphib- more insects (including mosquitoes) than 6,700 or more amphibian species are hav- ians at various points in their life cycles. do birds. In some habitats, the extinction ing difficulty adapting to rapid changes For example, frog eggs have no shells to of certain amphibian species could lead that have taken place in their water and protect frog embryos from water pollut- to extinction of certain species of other land habitats during the past few decades. ants, and adult frogs are often exposed to amphibians, aquatic insects, reptiles, birds, Such changes have resulted primarily from insecticides contained in the many insects fish, and mammals that feed on amphib- human activities such as use of pesticides they eat. We explore these and other fac- ians or their larvae. and other chemicals that become water tors later in this chapter. Third, amphibians are a genetic store- pollutants. Why should we care if some amphib- house of pharmaceutical products waiting Since 1980, populations of hundreds ian species become extinct? Scientists to be discovered. For example, compounds of amphibian species throughout the give three reasons. First, amphibians are in secretions from the skin of certain amphibians have been isolated and used as painkillers and antibiotics, and in treat- ments for burns and heart disease. Many scientists believe that the threats to amphibians present a warning about a number of environmental threats to biodiversity. In this chapter, we will learn about biodiversity, about how it has arisen and why it is important, and about how it is threat- ened. We will also look at some possible solutions to these problems. Joel Sartore/National Geographic Creative Figure 4-1 These are specimens of some of the nearly 200 amphibian spe- cies that have gone extinct since 1970. 78 CHAPTER 4 BIODIVERSITY AND EVOLUTION Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 4-1 What Is Biodiversity and Why Is It Important? CONCEPT 4 - 1 four components of the earth’s biodiversity provide us The biodiversity found in genes, species, ecosystems, with the ecosystem services (Figure 1-3, orange items, and ecosystem processes is vital to sustaining life on p. 7) that sustain us and our economies. earth. Recall that a species is a group of organisms with a set of characteristics that distinguish it from other groups of Biodiversity Is a Crucial Part of the Earth’s organisms, and in sexually reproducing organisms, indi- viduals must be able to mate and produce fertile offspring Natural Capital in order to be grouped within a species. Biological diversity, or biodiversity, is the variety of We do not know how many species there are on the the earth’s species, or varying life-forms, the genes they earth. Estimates range from 8 million to 100 million. In contain, the ecosystems in which they live, and the eco- 2011, a team of biologists led by Camilo Mora and Boris system processes such as energy flow and nutrient cycling Worm estimated that there are about 7–10 million species. that sustain all life (Figure 4-2). Acting together, these Other scientific estimates put the number much higher. Functional Diversity Ecological Diversity The biological and chemical processes such as energy The variety of terrestrial and flow and matter recycling needed for the survival of species, aquatic ecosystems found in communities, and ecosystems. an area or on the earth. Solar Chemical nutrients energy (carbon dioxide, Heat oxygen, nitrogen, minerals) Heat Heat Decomposers Producers (bacteria, fungi) (plants) Consumers (plant eaters, Heat meat eaters) Heat © Cengage Learning Genetic Diversity Species Diversity The variety of genetic material The number and abundance of species within a species or a population. present in different communities. Figure 4-2 Natural capital: The major components of the earth’s biodiversity—one of the planet’s most important renewable resources and a key component of its natural capital (see Figure 1-3, p. 7). Question: Why do you think we should protect the earth’s biodiversity from our actions? Right side, Top left: Laborant/Shutterstock.com; Right side, Top right: leungchopan/Shutterstock.com; Right side, Top center: ©Elenamiv/Shutterstock.com; Bottom right: ©Juriah Mosin/Shutterstock.com Section 4-1 79 Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. SCIENCE FOCUS 4.1 INSECTS PLAY A VITAL ROLE IN OUR WORLD Nicole Duplaix/National Geographic Creative We classify many insect species as pests half the species of insects we call pests. because they compete with us for food, This free pest control service is an impor- spread human diseases such as malaria, tant part of the earth’s natural capital. bite or sting us, and invade our lawns, Some insects also play a key role in loosen- gardens, and houses. Some people fear ing and renewing the topsoil that supports insects and many think the only good bug plant life on land. Others such as the dung is a dead bug. They fail to recognize the beetle recycle animal wastes (dung) often vital roles insects play in helping to sustain by rolling it into balls (Figure 4-B) and bury- life on earth. ing it for use as food. For example, pollination is a vital eco- Insects have been around for at least Figure 4-B A dung beetle rolls a ball of dung. system service that allows flowering plants 400 million years—about 2,000 times lon- Dung beetles can roll up to 10 times their to reproduce sexually when pollen grains ger than the latest version of the human body weight—equivalent to a 68-kilogram are transferred from the flower of one species. Some species reproduce at an (150-pound) person rolling a 680-kilogram plant to a receptive part of the flower of astounding rate and can rapidly develop (1,500-pound) boulder. another plant of the same species. Many of new genetic traits such as resistance to the earth’s plant species depend on insects pesticides. They also have an exceptional idly expanding human population and its to pollinate their flowers (chapter-opening ability to evolve into new species when growing resource use per person. photo and Figure 4-A, left). faced with changing environmental condi- The scientific study of insects is called Insects that eat other insects—such as tions, and many species are now being entomology—a field that includes a vast the praying mantis (Figure 4-A, right)— challenged to do so because of environ- number of subspecialties and applications. help to control the populations of at least mental changes brought about by the rap- Entomologists are expanding their research in areas related to environmental threats to insect populations. Environmental changes, many of them caused by human activities, are making such threats clearer every year. For example, entomologist Diana Cox- Darlyne A. Murawski/National Geographic Creative Foster of Pennsylvania State University (USA) is studying the decline of honeybees, which are extremely important pollinators. Her lab work focuses on colony collapse Dr. Morley Read/Shutterstock.com disorder, the name given to the disap- pearances of many bee colonies in recent years. This disorder is threatening to disrupt whole ecosystems that depend on bees for pollination, as well as much of the human food supply. We discuss this serious envi- ronmental problem more fully in Chapter 9. Figure 4-A Importance of insects: Bees (left) and numerous other insects pollinate flowering plants that serve as food for many plant eaters, including humans. This praying mantis, which is eating a Critical Thinking moth (right), and many other insect species help to control the populations of most of the insect spe- Identify three insect species not discussed cies we classify as pests. above that benefit your life. So far, biologists have identified about 2 million species— Species diversity, the number and variety of the species most of them being insects (Science Focus 4.1). Up to half present in any biological community, is the most obvi- of the world’s land-based plant and animal species live ous component of biodiversity. We discuss it in greater in tropical rain forests. Scientists believe that most of the detail in Section 4-5. Another important component is unidentified species live in the planet’s rain forests and in genetic diversity, the variety of genes found in a popula- the largely unexplored oceans. tion or in a species (Figure 4-3). The earth’s many spe- 80 CHAPTER 4 BIODIVERSITY AND EVOLUTION Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  wetlands—is another major component of biodiversity. Each of these ecosystems is a storehouse of genetic and species diversity. Biologists have classified the terrestrial (land) ecosystems into biomes—large regions such as forests, deserts, and grasslands with distinct climates and certain species (especially vegetation) adapted to them. Figure 4-4 shows different major biomes along the 39th parallel spanning the United States. We discuss biomes in more detail in Chapter 7. Yet another important component of biodiversity is functional diversity—the variety of processes such as energy flow and matter cycling that occur within ecosystems (see Figure 3-10, p. 59) as species interact with one another in food chains and © Cengage Learning webs. The earth’s biodiversity is a vital part of the nat- ural capital (see Figure 1-3, p. 7) that helps to keep us alive and supports our economies. With the help of technology, we use biodiversity to provide us with food, Figure 4-3 Genetic diversity among individuals in this population of wood, fibers, energy from wood and biofuels, and medi- a species of Caribbean snail is reflected in the variations in shell color cines. Biodiversity also plays critical roles in providing and banding patterns. Genetic diversity can also include other varia- us with the ecosystem services that preserve the qual- tions such as slight differences in chemical makeup, sensitivity to vari- ity of the air and water, maintain the fertility of topsoil, ous chemicals, and behavior. decompose and recycle wastes, and control populations of species that we call pests. The four components of cies contain a vast variety of genes, which enable life on biodiversity also increase the stability of ecosystems and the earth to survive and adapt to dramatic environmen- increase the resistance of ecosystems to harmful inva- tal changes. sive species. We owe much of what we know about bio- Ecosystem diversity—the earth’s variety of deserts, diversity to a fairly small number of researchers, such as grasslands, forests, mountains, oceans, lakes, rivers, and Edward O. Wilson (Individuals Matter 4.1). Denver Baltimore San Francisco St. Louis Las Vegas Coastal mountain Sierra Nevada Great American Rocky Great Mississippi Appalachian ranges Desert Mountains Plains River Valley Mountains © Cengage Learning Coastal chaparral Coniferous forest Desert Coniferous forest Prairie grassland Deciduous forest and scrub Figure 4-4 The major biomes found along the 39th parallel across the United States show a variety of ecosystems. The differences in tree and other plant species reflect changes in climate, mainly differ- ences in average annual precipitation and temperature. First: ©Zack Frank/Shutterstock.com; Second: Robert Crum/Shutterstock.com; Third: Joe Belanger/Shutterstock.com; Fourth: ©Protasov AN/ Shutterstock.com; Fifth: ©Maya Kruchankova/Shutterstock.com; Sixth: © Marc von Hacht/Shutterstock.com Section 4-1 81 Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  individuals matter 4.1 Edward O. Wilson: A Champion of Biodiversity As a boy growing up in the southeastern United States, Edward O. Wilson became interested in insects at the age of nine. He has said, “Every kid has a bug period. I never grew out of mine.” Before entering college, Wilson had decided he would Jim Harrison specialize in the study of ants. After he grew fascinated with that tiny organism, and throughout his long career, he steadily widened his focus to include the entire biosphere. He now spends much of his time studying, writing, and speaking about biodiversity and working on Harvard University’s Encyclopedia of Life, an online database for the planet’s known and named species. During his long career, Wilson has taken on many challenges. He and other researchers working together discovered how ants communicate using chemicals called pheromones. He also stud- ied the complex social behavior of ants and has compiled much of his work into the epic volume, The Ants, published in 1990. His ant research has been applied to the study and understand- ing of other social organisms, including humans. He has also proposed the hypothesis that humans have a natural affinity for wildlife and wild places—a concept he calls biophilia (or love of life). One of Wilson’s landmark works is The Diversity of Life, pub- lished in 1992, in which he put together the principles and prac- tical issues of biodiversity more completely than anyone had to that point. Wilson is now deeply involved in writing and lectur- ing about the need for global conservation efforts and is pro- moting the goal of completing a global survey of biodiversity. He has won more than 100 national and international awards and has written 25 books, two of which won the Pulitzer Prize for General Nonfiction. About the importance of biodiversity, he writes: “Until we get serious about exploring biological diversity... science and humanity at large will be flying blind inside the biosphere.... How can we save Earth’s life forms from extinction if we don’t even know what most of them are?” Background photo: Christian Musat/Shutterstock.com 82 CHAPTER 4 BIODIVERSITY AND EVOLUTION Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 4-2 How Does the Earth’s Life Change over Time? CONCEPT 4 - 2 A individuals in that population were more likely to survive The scientific theory of evolution explains how life on and produce offspring that had the same specific advan- the earth changes over time due to changes in the genes tage. The advantage was due to a characteristic, or trait, of populations. possessed by these individuals but not by others of their kind. CONCEPT 4 - 2 B Based on these observations, Darwin and Wallace Populations evolve when genes mutate and give some described a process called natural selection, in which individuals genetic traits that enhance their abilities individuals with certain traits are more likely to survive to survive and to produce offspring with these traits and reproduce under a particular set of environmen- (natural selection). tal conditions than are those without the traits (Concept 4-2B). The scientists concluded that these survival traits Biological Evolution by Natural Selection would become more prevalent in future populations of the species as individuals with those traits became more Explains How Life Changes over Time numerous and passed their traits on to their offspring. Most of what we know about the long history of life on A huge body of evidence supports this idea. As a the earth comes from fossils: mineralized or petrified result, biological evolution through natural selection has replicas of skeletons, bones, teeth, shells, leaves, and become an important scientific theory that generally seeds, or impressions of such items found in rocks (Fig- explains how life has changed over the past 3.5 billion ure 4-5). Scientists also drill core samples from glacial ice years and why life is so diverse today. However, there at the earth’s poles and on mountaintops, and examine are still many unanswered questions that generate sci- the signs of ancient life found at different layers in these entific debate about the details of evolution by natural cores. selection. The entire body of evidence gathered using these methods, which is called the fossil record, is uneven and incomplete. Some forms of life left no fossils, and some fossils have decomposed. The fossils found so far repre- sent probably only 1% of all species that have ever lived. Trying to reconstruct the development of life with so little evidence is the work of paleontology—a challenging scien- tific detective game. Green Careers: paleontologist How did we end up with such an amazing array of species? The scientific answer involves biological evo- lution (or simply evolution): the process whereby the earth’s life changes over time through changes in the genes of populations of organisms in succeeding genera- tions (Concept 4-2A). According to the theory of evolu- tion, all species evolved from earlier, ancestral species. In other words, life comes from life. The idea that organisms change over time and are descended from a single common ancestor has been around in one form or another since the early Greek philosophers. But no one had developed a convincing Ira Block/National Geographic Creative explanation of how this could happen until 1858 when naturalists Charles Darwin (1809–1882) and Alfred Russel Wallace (1823–1913) independently proposed the concept of natural selection as a mechanism for biological evolution. Darwin meticulously gathered evidence for this idea and published it in 1859 in his book, On the Origin of Species by Means of Natural Selection. Darwin and Wallace observed that individual organ- isms must struggle constantly to survive by getting Figure 4-5 This fossil shows the mineralized remains of an early enough food, water, and other resources, to avoid being ancestor of the present-day horse. It roamed the earth more than eaten, and to reproduce. They also observed that individ- 35 million years ago. Note that you can also see fish skeletons on this uals in a population with a specific advantage over other fossil. Section 4-2 83 Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  Mutations and Changes in the Genetic and pass this helpful trait on to more offspring. Thus, the scientific concept of natural selection explains how popu- Makeup of Populations Lead to Biological lations adapt to changes in environmental conditions. Evolution by Natural Selection Another important example of natural selection at The process of biological evolution by natural selec- work is the evolution of genetic resistance—the ability of one tion involves changes in a population’s genetic makeup or more organisms in a population to tolerate a chemical through successive generations. Note that populations—not designed to kill it. Such resistance develops fairly quickly individuals—evolve by becoming genetically different. in populations of organisms that produce large numbers of The first step in this process is the development of offspring, such as many species of bacteria and insects. genetic variability, or variety in the genetic makeup of indi- For example, certain bacteria (Figure 4-6a) have devel- viduals in a population. This occurs through mutations: oped genetic resistance to widely used antibacterial drugs, changes in the DNA molecules of a gene in any cell that or antibiotics, which have become a force of natural selec- can be inherited by offspring. Most mutations result from tion. Often, when such drugs are used (Figure 4-6b), a few random changes that occur in coded genetic instructions bacteria that are genetically resistant to them survive and when DNA molecules (see Figure 9, p. S17, in Supple- rapidly produce more offspring than the bacteria that were ment 4) are copied each time a cell divides and whenever killed by the drug could have produced (Figure 4-6c). Thus, an organism reproduces. Some mutations also occur from the antibiotic eventually loses its effectiveness as genetically exposure to external agents such as radioactivity and nat- resistant bacteria keep reproducing while those that are ural and human-made chemicals (called mutagens). susceptible to the drug die off (Figure 4-6d). (We discuss Mutations can occur in any cell, but only those that this form of genetic resistance further in Chapter 17.) take place in genes of reproductive cells are passed on to One way to summarize the process of biological evo- offspring. Sometimes, such a mutation can result in a new lution by natural selection is: Genes mutate, individuals are genetic trait, called a heritable trait, which can be passed from selected, and populations evolve such that they are better adapted one generation to the next. In this way, populations develop to survive and reproduce under existing environmental conditions differences among individuals, including genetic variability. (Concept 4-2B). The next step in biological evolution is natural selection, A remarkable example of species evolution by natural in which environmental conditions favor some individu- selection is Homo sapiens sapiens. We have evolved certain als over others. The favored individuals possess heritable traits that have allowed us to dominate most of the earth traits that give them some advantage over other indi- (Case Study that follows). viduals in a given population. Such a trait is called an adaptation, or adaptive trait—any heritable trait that CASE STUDY improves the ability of an individual organism to survive How Did Humans Become Such a Powerful and to reproduce at a higher rate than other individuals in Species? a population are able to do under prevailing environmen- tal conditions. For example, in the face of snow and cold, Like many other species, humans have survived and a few gray wolves in a population that have thicker fur thrived because we have certain traits that allow us to might live longer and thus produce more offspring than adapt to and modify parts of the environment to increase do those without thicker fur. As those longer-lived wolves our chances of surviving and reproducing. mate, genes for thicker fur spread throughout the popula- Evolutionary biologists attribute our success to three tion and individuals with those genes increase in number adaptations: strong opposable thumbs that allowed us to grip a. b. c. d. © Cengage Learning Normal bacterium Resistant bacterium Figure 4-6 Evolution by natural selection. A population of bacteria (a) is exposed to an antibiotic, which (b) kills most individuals, but none of those possessing a trait that makes them resistant to the drug (shown in red). The resistant bacteria multiply (c) and eventually, (d) replace all or most of the nonresistant bacteria. 84 CHAPTER 4 BIODIVERSITY AND EVOLUTION Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. and use tools better than the few other animals that have thumbs could do; an ability to walk upright, which gave us agility and freed up our hands for many uses; and a complex brain, which allowed us to develop many skills, including the ability to use speech and to read and write to transmit complex ideas (Figure 4-7). These adaptations have helped us to develop tools, weapons, protective devices, and technologies that extend our limited senses of sight, hearing, and smell. Thus, in an eye-blink of the 3.5-billion-year history of life on earth, we have developed powerful technologies and taken over Mary Lane/Shutterstock.com much of the earth’s net primary productivity for our own use. At the same time, we have degraded much of the planet’s life-support system as our ecological footprints have grown (see Figure 1-13, p. 14). However, adaptations that make a species successful dur- ing one period of time may not be enough to ensure the spe- cies’ survival when environmental conditions change. This is Figure 4-8 One type of carnivorous plant is the Venus flytrap. A fly no less true for humans, and some environmental conditions or other small insect, entering a hinged opening on the plant’s leaf, are now changing rapidly, largely due to our own actions. touches trigger hairs that cause the opening to snap shut in less than (We focus on several such changes in later chapters.) a second and trap its prey. The plant then uses enzymes to digest its One of our adaptations—our powerful brain—may prey over a period of 1–2 weeks. enable us to live more sustainably by understanding and copying the ways in which nature has sustained itself for mosquitoes, rats, bacteria, and cockroaches—often adapt billions of years, despite major changes in environmental to a change in environmental conditions in a short time conditions. (days to years). By contrast, species that cannot produce large numbers of offspring rapidly—such as elephants, Adaptation through Natural Selection tigers, sharks, and humans—take a much longer time (typically thousands or even millions of years) to adapt Has Limits through natural selection. In the not-too-distant future, will adaptations to new environmental conditions through natural selection allow our skin to become more resistant to the harmful effects Three Common Myths about Evolution of UV radiation, our lungs to cope with air pollutants, and through Natural Selection our livers to better detoxify pollutants in our bodies? Evolution experts have identified three common miscon- According to scientists in this field, the answer is no ceptions about biological evolution through natural selec- because of two limitations on adaptation through natural tion. One is that “survival of the fittest” means “survival of selection. First, a change in environmental conditions can the strongest.” To biologists, fitness is a measure of repro- lead to such an adaptation only for genetic traits already ductive success, not strength. Thus, the fittest individuals present in a population’s gene pool or for traits resulting are those that leave the most descendants. from mutations, which occur randomly. Another misconception is that organisms develop Second, even if a beneficial heritable trait is present in certain traits because they need them. For example, cer- a population, the population’s ability to adapt may be lim- tain plants, called carnivorous plants (Figure 4-8), feed on ited by its reproductive capacity. Populations of genetically insects not because they once needed to in order to sur- diverse species that reproduce quickly—such as weeds, vive. Rather, some ancestors of these plants had char- acteristics that enabled them to trap insects and to draw nutrients from them. This trait gave them an advantage over other plants in an environment where there were lots of insects available, and this enabled them to produce more offspring that had such characteristics. Thus, over © Cengage Learning time, their populations grew and continued to evolve in this way. A third misconception is that evolution by natural selection involves some grand plan of nature in which Figure 4-7 Homo sapiens sapiens has had three advantages over species become more perfectly adapted. From a scientific other mammals that helped the species to survive certain pressures of standpoint, no plan or goal for genetic perfection has been natural selection and become a dominant species on planet Earth. identified in the evolutionary process. Section 4-2 85 Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  4-3 How Do Geological Processes and Climate Change Affect Evolution? CONCEPT 4 - 3 sudden movement of tectonic plates can cause earth- Tectonic plate movements, volcanic eruptions, quakes, which can also affect biological evolution by caus- earthquakes, and climate change have shifted wildlife ing fissures in the earth’s crust that can separate and iso- habitats, wiped out large numbers of species, and late populations of species. Over long periods of time, this created opportunities for the evolution of new species. can lead to the formation of new species as each isolated population changes genetically in response to new envi- ronmental conditions. Volcanic eruptions that occur along Geological Processes Affect Natural the boundaries of tectonic plates can also affect biological Selection evolution by destroying habitats and reducing, isolating, or wiping out populations of species (Concept 4-3). The earth’s surface has changed dramatically over its long history. Scientists have discovered that huge flows of molten rock within the earth’s interior have broken its Climate Change and Catastrophes Affect surface into a series of gigantic solid plates, called tectonic Natural Selection plates. For hundreds of millions of years, these plates have drifted slowly on the planet’s mantle (Figure 4-9). Throughout its history, the earth’s climate has changed Rock and fossil evidence indicates that 200–250 mil- drastically. At times, it has cooled and covered much of lion years ago, all of the earth’s present-day continents the earth with glacial ice. At other times it has warmed, were connected in a super continent called Pangaea (Fig- melted that ice, and drastically raised sea levels, which in ure 4-9, left). About 135 million years ago, Pangaea began turn increased the total area covered by the oceans and splitting apart as the earth’s tectonic plates moved, even- reduced the earth’s total land area. Such alternating peri- tually resulting in the present-day locations of the conti- ods of cooling and heating have led to the advance and nents (Figure 4-9, right). retreat of ice sheets at high latitudes over much of the The fact that tectonic plates drift has had two impor- northern hemisphere, most recently about 18,000 years tant effects on the evolution and distribution of life on the ago (Figure 4-10). earth. First, the locations of continents and oceanic basins These long-term climate changes have had a major have greatly influenced the earth’s climate and thus have effect on biological evolution by determining where dif- helped to determine where plants and animals can live. ferent types of plants and animals can survive and thrive, Second, the movement of continents has allowed species to and by changing the locations of different types of ecosys- move, adapt to new environments, and form new species tems such as deserts, grasslands, and forests (Concept 4-3). through natural selection. When continents join together, Some species became extinct because the climate changed populations can disperse to new areas and adapt to new too rapidly for them to adapt and survive, and new spe- environmental conditions. When continents separate and cies evolved to take over their ecological roles. when islands are formed, populations must evolve under Another force affecting natural selection has been isolated conditions or become extinct. catastrophic events such as collisions between the earth Adjoining tectonic plates that are grinding along and large asteroids. There may have been many of these slowly next to one another sometimes shift quickly. Such collisions during the 3.5 billion years of life on earth. 225 million Present years ago EURASIA NORTH AMERICA A AFRICA AE G N PA SOUTH © Cengage Learning AMERICA AUSTRALIA ANTARCT I CA Figure 4-9 Over millions of years, the earth’s continents have moved very slowly on several gigantic tectonic plates. Question: How might an area of land splitting apart cause the extinction of a species? 86 CHAPTER 4 BIODIVERSITY AND EVOLUTION Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  18,000 Northern Hemisphere Modern day years before Ice coverage (August) (Compiled by the authors using data from the National Oceanic and Atmospheric Administration.) present Legend Continental ice Sea ice Land above sea level Figure 4-10 These maps of North America show the large-scale changes in glacial ice coverage dur- ing the past 18,000 years. Question: What are two characteristics of an animal and two characteris- tics of a plant that natural selection would have favored as these ice sheets (left) advanced? Such impacts have caused widespread destruction of eco- On a long-term basis, the three scientific principles systems and wiped out large numbers of species. On the of sustainability (see Figure 1-2, p. 6 or back cover), other hand, they have also caused shifts in the locations especially the biodiversity principle (Figure 4-2), of ecosystems and created opportunities for the evolution have enabled life on the earth to adapt to drastic of new species. changes in environmental conditions. 4-4 How Do Speciation, Extinction, and Human Activities Affect Biodiversity? CONCEPT 4 - 4 A where its members can no longer breed and produce fer- As environmental conditions change, the balance tile offspring with members of another population that between the formation of new species and the extinction did not change or that evolved differently. of existing species determines the earth’s biodiversity. The most common way in which speciation occurs, especially among sexually reproducing species, is when a CONCEPT 4 - 4 B barrier or distant migration separates two or more popula- Human activities are decreasing biodiversity by causing the tions of a species and prevents the flow of genes between extinction of many species and by destroying or degrading them. This happens in two phases: first geographic isola- habitats needed for the development of new species. tion, and then reproductive isolation. Geographic isolation occurs when different groups of the same population of a species become physically How Do New Species Evolve? isolated from one another for a long period of time. For Under certain circumstances, natural selection can lead example, part of a population may migrate in search of to an entirely new species. In this process, called specia- food and then begin living as a separate population in tion, one species splits into two or more different species. another area with different environmental conditions. For sexually reproducing organisms, a new species forms Populations can also be separated by a physical barrier when one population of a species has evolved to the point (such as a mountain range, stream, or road), a volcanic Section 4-4 87 Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.  that they cannot produce live, fertile offspring if they are rejoined and attempt to interbreed. As a result, one species has become two, and speciation has occurred (Figure 4-12). Humans are playing an increasing role in the process of speciation. We have learned to shuffle genes from one spe- cies to another through artificial selection and, more recently, through genetic engineering (Science Focus 4.2). All Species Eventually Become Extinct Another process affecting the number and types of species on the earth is extinction, the process in which an entire species ceases to exist (also referred to as biological extinction; Brandon Alms/Shutterstock.com when a species becomes extinct over a large region, but not globally, it is called local extinction). When environmental con- ditions change dramatically or rapidly, a population of a spe- cies faces three possible futures: adapt to the new conditions through natural selection, migrate (if possible) to another area with more favorable conditions, or become extinct. Species that are found in only one area, called endemic Figure 4-11 These poison dart frogs vary in coloration, partly species, are especially vulnerable to extinction. They exist because they were exposed to different environmental conditions. on islands and in other unique areas, especially in tropi- cal rain forests where most species have highly specialized roles. For these reasons, they are unlikely to be able to eruption, tectonic plate movements, or winds or flowing migrate or adapt in the face of rapidly changing environ- water that carry a few individuals to a distant area. These mental conditions. Many of these endangered species are separated populations can develop quite different char- amphibians (Core Case Study). One example is the golden acteristics. For example, populations of poison dart frogs toad (Figure 4-13), which apparently became extinct in (Core Case Study) living on different islands or in different 1989 even though it lived in the well-protected Monteverde parts of a region can have dramatic differences in color- Cloud Forest Reserve in the mountains of Costa Rica. ation, as shown in Figure 4-11. Fossils and other scientific evidence indicate that all In reproductive isolation, mutation and change by species eventually become extinct, but drastic changes in natural selection operate independently in the gene pools environmental conditions can eliminate large groups of of geographically isolated populations. If this process con- species relatively rapidly. Throughout most of the earth’s tinues long enough, members of the geographically and long history, species have disappeared at a low rate, called reproductively isolated populations of sexually reproduc- the background extinction rate. Based on the fossil ing species may become so different in genetic makeup record and analysis of ice cores, biologists estimate that Arctic Fox Adapted to cold through heavier fur, short ears, short legs, and short nose. White fur matches snow for Northern camouflage.