Chapter 4Evolution and Biodiversity

Summary

1. Life emerged on the earth through two phases of development: a chemical evolution of the organic molecules, biopolymers, and systems of chemical reactions to form the first cells and the biological evolution from single-celled prokaryotic bacteria to single-celled eukaryotic creatures, and then to multicellular organisms.

2. Evolution is the change in a population’s genetic makeup over time. Evolution forces adaptations to changes in environmental conditions in a population. The diversity of life on earth reflects the wide variety of adaptations necessary and suggests that environmental conditions have varied widely over the life of the earth.

3. An ecological niche is a species’ way of life or its functional role in a community. Everything that affects its survival and reproduction (temperature tolerance, water needs, space needs, interactions with other organisms, etc.) is a part of that niche. The ecological niche helps a population survive by the adaptive traits that its organisms have acquired.

4. Extinction of species and formation of new species constantly change the biodiversity of the earth.

5. In the future, evolution will continue to influence our environment. Man’s use of artificial selection and genetic engineering to evolve species may have unintended consequences because evolution is a long, slow process and is unpredictable.

Key Questions and Concepts

4-1 What is biodiversity and why is it important?CORE CASE STUDY. Alligators act as a keystone species, yet their numbers were seriously compromised by over-hunting. Their activities provide important habitat for fish and avian species. They also control populations by their feeding behaviors. In 1967 the alligator was placed on the endangered species list and has made a dramatic recovery.

A. Biodiversity is the variety of species, genes, ecosystems, and ecosystem processes.1. Species diversity, genetic diversity, ecosystem diversity, and functional diversity.

4-2 Where do species come from?A. Evolution is the change in a population’s genetic makeup over time.B. Populations evolve by becoming genetically different.C. All species descend from earlier, ancestral species—theory of evolution.

1. Over time, a population’s gene pool changes when mutations (beneficial changes) in DNA molecules are passed on to offspring. a. Mutations are random changes in the structure/number of DNA molecules in a cell.b. Mutations occur in two ways.

1) Gene DNA is exposed to external agents like X-rays, chemicals (mutagens), or radioactivity.2) Random mistakes that occur in coded genetic instructions.

D. Natural selection occurs when members of a population have genetic traits that improve their ability to survive and produce offspring with those specific traits.1. For natural selection to evolve in a population, three conditions are necessary:

a. The population must have genetic variability.b. The trait must be heritable, capable of being passed from one generation to another.c. The trait must enable individuals with the trait to produce more offspring than individuals without

the trait; this is differential reproduction.2. Adaptation or adaptive traits are heritable traits that help organisms to survive and reproduce better

under prevailing environmental conditions.

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CASE STUDY. Humans have thrived so well as a species because of their strong opposable thumbs, ability to walk upright, and complex brain. These adaptations may not prove as beneficial as the environment continues to change, though our powerful brain may allow us to live more sustainably in the future.

E. Natural selection can only act on existing genes and is limited by reproductive capacity.

4-3 How do geologic processes and climate change affect evolution?A. Processes such as the shifting of tectonic plates, volcanic eruptions, and earthquakes influence earth’s

climate and in turn affect evolution by removing and/or isolating habitats and species.B. Long-term climate changes relocate ecosystems, thus determining where certain species can live.C. Asteroids and meteorites have caused environmental stress and mass extinctions.

SCIENCE FOCUS: the conditions that make Earth suitable for life.

4-4 How do speciation, extinction, and human activities affect biodiversity?A. Natural selection can lead to development of an entirely new species.

In speciation, two species arise from one when some members of a population cannot breed with other members to produce fertile offspring. Speciation occurs in two phases:1. Geographic isolation, physical separation for long time periods.2. Reproductive isolation.

B. When population members cannot adapt to changing environmental conditions, the species becomes extinct.

C. When local environmental conditions change, some species will disappear at a low rate; this is called background extinction.

D. Mass extinction is a significant rise in extinction rates above the background extinction level. Usually, 25–70% of species are lost. Recent evidence suggests that there have been two mass extinctions on earth. There appear to have been three mass extinctions on earth.SCIENCE FOCUS: Artificial ways to control population genetics include artificial selection and genetic engineering.

4-5 What is species diversity and why is it important?A. Species diversity is the number of species (richness) combined with their relative abundance (evenness).B. Species rich communities tend to be more stable and more productive.

SCIENCE FOCUS: the size of a habitat affects the species richness of that habitat island

4-6 What roles do species play in ecosystems?A. Ecological niche is a species’ way of life in an ecosystem, everything that affects its survival and

reproduction.1. The niche includes the members’ adaptations; its range of tolerance for physical and chemical

conditions, its interactions with other components of the ecosystem, and its role in energy flow and matter recycling.

2. The fundamental niche is the full potential range of conditions and resources a species could potentially use. Its realized niche is the part of the potential niche that allows a species to survive and avoid competition with other species for the same resources.

B. Some species have broad ecological roles and are termed generalist species.C. Some species have narrow ecological roles and are termed specialist species.

CASE STUDY. Cockroaches are the ultimate generalists. The can survive extreme conditions and have a wide variety of adaptations that allow them to avoid predation. By contrast, many species are narrow specialists, though they sometimes have an advantage in their environment because they have few competitors.

D. Niches can be occupied by native or non-native species.E. Indicator species provide early warning of ecosystem damage because they have a narrow range of

tolerance. CASE STUDY. Amphibians are indicator species that are declining globally. Factors affecting their survival include habitat loss, drought, pollution, increase in UV radiation, parasites, fungal diseases, climate change, overhunting, and introduction of non-native species. Their role as indicator species is cause for alarm on a global scale.

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H. Keystone species have a large affect on maintaining balance within an ecosystem. 1. Can be, but are not necessarily, pollinators and top predators. 2. Foundation species create and enhance habitats that benefit other species.CASE STUDY. Sharks are keystone species that have been overlooked by conservation efforts because of human bias. They tend to be considered dangerous and have gone without protection despite being heavily fished for their valuable fins. They also commonly drown in fishing nets. Shark populations have been declining since the 1970s, and scientists are now calling for a ban on shark finning in international waters.

Teaching Tips

Large Lecture Courses:

Pick two species that students would be familiar with from the local environment (perhaps something from the urban edge, such as coyotes or raccoons). One should be a generalist and one a specialist. Allow them to brainstorm ideas as you record them on the board. What are the characteristics of each? Which one are they more familiar with? Are humans more similar to the specialist or generalist?

Smaller Lecture Courses

Have students work in small groups researching a species that is an ecosystem engineer prior to this lecture. As an introduction, they can briefly present their species to the rest of the course, covering the ways in which the species alters its environment, and what advantages this has. Conclude with a compare/contrast discourse on the ways in which humans are similar or different from ecosystem engineers.

Key Terms

adaptation (p. 82)adaptive trait (p. 82)background extinction (p. 87)biological evolution (p. 80)differential reproduction (p. 82)ecological niche (p. 91)endemic species (p. 87)extinction (p. 87)fossils (p. 81)

gene splicing (p. 88)generalist species (p. 91)geographic isolation (p. 86)mass extinction (p. 88)mutations (p. 82)niche (p. 91)reproductive isolation (p. 86)specialist species (p. 92)speciation (p. 86)

Term Paper Research Topics

1. Evolution: the theory of evolution, supporting and detracting evidence, fossils; embryological homologies, structural homologies; biochemical evidence; DNA evidence. Contrast the views of slow, gradual change and relatively rapid (punctuated) change.

2. Biological Evolution: endosymbiont hypothesis; Gaia hypothesis; extinctions and radiations; natural selection and genetic drift; adaptations and their limits; gradualism and punctuated equilibrium.

3. Diversity of species: choose a kingdom.

4. Genetic engineering: how humans are changing the course of evolution.

5. Scientific methods: genetic engineering; DNA analysis.

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Discussion Topics

1. To what extent should humans take evolution into their own hands?

2. Should there be limits on genetic engineering?

3. How does the change that humans create through cultural evolution compare to the process of evolution by natural selection?

Activities/Projects

1. As a class exercise, evaluate the diversity of your community using criteria such as ethnic, racial, religious, and socioeconomic groups; lifestyles; and industries, landscape features, and landscape forms. What elements of diversity have proved troublesome? What additional elements of diversity would improve your community?

2. Invite an evolutionary biologist to your class. Ask about evidence for different parts of the theory of evolution, including the endosymbiont hypothesis. Ask about the Gaia hypothesis.

3. Arrange a field trip providing opportunities to compare and contrast ecosystems of several different types, including some damaged or stressed by human activities. Invite an ecologist or biologist along to identify and discuss specific examples of species adaptation to environmental conditions. Do the boundaries between different kinds of ecosystems tend to be sharply delineated? Can you identify factors that limit the growth of certain species?

4. As a class, consider the crops that provide the majority of our food. Brainstorm a list of "designer genes" that would improve those crops for human consumption. Reflect on how genetic engineering alters the relationship between humans and evolution. Consider the power and the limits of that relationship.

Attitudes and Values1. Do you think that biodiversity is an ecosystem service? Explain.

2. Do you think you have a responsibility to sustain biodiversity?

3. Do you think evolution of species has occurred? If so, how?

4. Do you think species have a right to struggle to survive without human interference?

ABC News Videos

Circle of Life; Environmental Science in the Headlines, 2008, DVD ISBN: 0495561908Global Warning: Where Have the Wild Things Gone? Environmental Science in the Headlines, 2008, DVD ISBN: 0495561908Bald Eagle Soars Again: Taken Off Endangered Species List; Environmental Science in the Headlines, 2008, DVD ISBN: 0495561908

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Additional Video Resources

Beavers: IMAX (1998)An engaging look at the charismatic ecosystem engineers.http://www.imax.com/ImaxWeb/filmDetail.do?type=nowPlaying&movieID=code__.__12667

Nova—Evolution: Extinction!Main Website: http://www.pbs.org/wgbh/evolution/extinction/ Teachers Guide: http://www.pbs.org/wgbh/nova/teachers/programs/0000_evoextin.html

Planet Earth (BBC Series, 5 discs)An exploration of global ecosystems.http://www.bbc.co.uk/nature/animals/planetearth/

Web Resources

IUCN Red ListThe IUCN Species Survival Commission’s list of threatened and endangered species around the globe.http://www.iucnredlist.org

Encyclopedia of LifeAn attempt to document all species of life on earth.http://www.eol.org

Suggested Answers to End of Chapter Questions

The following are examples of the material that should be contained in possible student answers to the end of chapter Critical Thinking questions. They represent only a summary overview and serve to highlight the core concepts that are addressed in the text. It should be anticipated that the students will provide more in-depth and detailed responses to the questions depending on an individual instructor’s stated expectations.

1. List three ways you could apply concept 4-4B in order to live a more environmentally sustainable lifestyle.

Answers may vary. Students may suggest that they would attempt to limit the effects of habitat fragmentation by planting native vegetation in their yards in order to create or contribute to a habitat corridor. They could limit the extent to which their economic activities support deforestation and habitat loss in foreign countries. They might also pursue political activity to oppose massive habitat loss through the conversion of land into agriculture or suburban land uses.

2. Explain what would happen to the ecosystem where American alligators live (Core Case Study) if the alligators went extinct. Name a plant species and an animal species that would be seriously affected, and describe how each might respond to these changes in their environmental conditions.

The ecosystem would be very much altered because the alligator acts as a keystone species. Native plants would suffer as trees and shrubs took over the habitat. Many fish species and migratory birds would also suffer from the loss of alligators.

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3. What role does each of the following processes play in helping implement the four scientific principles of sustainability: (a) natural selection, (b) speciation, and (c) extinction?

(a) Natural selection implements all four principles of sustainability. Solar energy produces the plants that provide the energy and food for a great biodiversity of creatures living on the planet. Predator-prey relationships help to maintain the “survival of the fittest” implications in natural selection and control population. The nutrients in the remains of the prey then get recycled back through the system.

(b) Speciation impacts the biodiversity principle of sustainability. The more new species arise as a result of speciation, the greater the biodiversity of the ecosystem. If the new species is a predator it could also impact the population control principle of sustainability.

(c) Extinction results directly in a loss of biodiversity as the species is lost from the gene pool. The nutrients in the species will be recycled through the ecosystem as the numbers decline until no more of the species are left. If the species that has become extinct was a predator species, then it could also impact the population control principle of sustainability.

4. Describe the major differences between the ecological niches of humans and cockroaches. Are these two species in competition? If so, how do they manage to coexist?

Both cockroaches and humans are generalist species having very broad niches. This means that they can live in many different places, eat a variety of foods, and tolerate a wide range of environmental conditions. Cockroaches have been around for 350 million years and have thrived throughout the evolutionary process. Humans are a recent addition to the planet. Cockroaches eat almost anything and can live anywhere except in the polar regions. They can go for a month without food, survive for a month on one drop of water, and can withstand high doses of radiation. Some cockroaches can even survive being frozen. These traits are in contrast to humans. Additionally humans do not reproduce as fast as cockroaches, which have a very high reproductive rate. Unlike humans, cockroaches also eat their own dead, and if food is scarce will even eat each other! Although cockroaches do live in homes that are occupied by humans, they are not directly in competition with each other for resources. However, cockroaches can evade been stepped on, as they have rapid response times, and the ability to see virtually in all directions at once. Cockroaches carry bacteria and viruses that cause diseases in humans, and can cause allergic responses in susceptible individuals.

5. How would you experimentally determine whether an organism is a keystone species?

A controlled experiment could be performed similar to the one conducted by Robert Paine on the rocky shoreline of the Pacific coast of Washington State. He demonstrated the keystone role of the top-predator sea star Piaster orchaceus in an intertidal zone community. Paine removed these mussel-eating sea stars from one rocky shoreline community but not from an adjacent community, which served as the control group. Mussels took over and crowded out many other species in the community without the Piaster sea stars. This type of experiment could be performed in other areas, with different species, to assess the role that certain species have in an ecosystem and whether a species could be classified as a keystone species.

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6. Is the human species a keystone species? Explain. If humans were to become extinct, what are three species that might also become extinct and three species whose population would probably grow?

Humans are likely a keystone species by virtue of their technology and the extreme manner in which they influence their habitat. Were we to become extinct, their domesticates would most likely not survive. These would include pets, livestock, and crop plants. Species whose populations would likely grow would be the ones human activities have had a detrimental effect on, such as whales, mountain gorillas, and the many weeds we struggle to keep in check.

7. How would you respond to someone who tells you: (a) that he or she does not believe in biological evolution by natural selection because it is “just a theory,” and (b) that we should not worry about air pollution because natural selection will enable humans to develop lungs that can detoxify pollutants?

(a) A theory is part of the process that scientists follow when investigating scientific evidence in order to explain their observations. For a theory to be validated it has to be accepted by the scientific community and reviewed by the world’s leading scientists. It has to stand up to scientific scrutiny. There is much fossil evidence to indicate that evolution through natural selection has taken place. There are also some examples that evolution is in action today as evidenced by the color changes in moths that has taken place since the industrial revolution. Indeed, evolution may just be a theory, but to date the theory has stood the test of time within the scientific world. Until a better scientific explanation is put forward it will remain the explanation of choice. Physicists and mathematicians give credence to the theory of relativity, because as yet no one has proven it wrong. Even Einstein said that a thousand experiments can prove him right, but it would take only one experiment to prove him wrong. As yet, that experiment has not been conducted so the theory of relativity, like the theory of evolution, remains the best scientific explanation of our observations.

(b) Unfortunately, with the human species and other large species that do not reproduce large numbers of offspring rapidly, natural selection will not take place quickly enough for our lungs to become resilient to air pollution. Maybe this adaptation could take place over thousands or even millions of years, but in someone’s own lifespan this is not feasible. It is more feasible to tackle the problem of air pollution and bring about its reduction, than it is to assume that humans will be able to adapt to these undesirable environmental conditions in the short term.

8. How would you respond to someone who says that because extinction is a natural process, we should not worry about the loss of biodiversity?

It is true that as environmental conditions change some species may begin to disappear at a low rate. This is the background extinction rate, and annually is around one to five species for every million species on the planet. However, scientists such as E. O. Wilson suggest that human activities have increased the extinction rate to somewhere between 100 and 1000 times the natural background rate. As more and more habitat is disturbed by human use and the resulting declines in biodiversity take place, we could lose many species from the earth over a relatively small time scale. Tropical rain forests, coral reefs, and wetlands are some of the most biodiverse areas on the earth, yet these are the regions that are under the most threat. Loss of biodiversity in these regions will have a major effect on the ecosystems and bring about extinction rates that are well above the naturally occurring background rates.

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9. Congratulations! You are in charge of the future evolution of life on the earth. What three things would you put on the top of your list to do?

Student answers will vary but could include: increased conservation, preservation, and protection of habitat that allows for greater biodiversity and ecosystem stability through continuing evolutionary processes; learn how to work and live within the four principles of sustainability and apply these to the human ecosystem; and address some of the main anthropogenic causes of environmental degradation and take measures to remedy these issues expediently to offset the negative effects that they may have on the evolution of species-global warming, ozone thinning, etc.

10. List two questions that you would like to have answered as a result of reading this chapter.

Student answers will vary and provide a good starting point

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