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Chapter 4
Biodiversity and Evolution
Chapter Review Questions and Outlines
Key Questions and Case Studies
CORE CASE STUDY: Why Are Amphibians Vanishing?
Amphibians were among the earliest vertebrates to emerge from the earth’s waters and live on land.
Historically, they have been able to adjust to and survive environmental changes more effectively than
any other species. The amphibian world is now changing rapidly. Many scientists believe that the threats
to amphibians present a warning about a number of environmental threats to biodiversity.
4-1 What is biodiversity and why is it important?
A. Biodiversity is the variety of species, genes, ecosystems, and ecosystem processes.
1. Species are individuals that can make and produce viable offspring.
2. Species diversity, genetic diversity, ecosystem diversity, and functional diversity.
a. Biomes are large regions with distinct climates and certain species that are adapted to them.
SCIENCE FOCUS: Insects Play a Vital Role in Our World
Insects often have a bad reputation and are considered pests. However the ecological roles they play
in pollinating flowering plants and controlling other insect populations make them invaluable to
humans.
4-2 How does the earth’s life change over time?
A. Most of what we know of the history of life comes from the fossil record.
B. Evolution is the change in a population’s genetic makeup over time.
C. All species descend from earlier, ancestral species—the theory of evolution.
1. Natural selection occurs when members of a population have genetic traits that improve their
ability to survive and produce offspring with those specific traits.
CASE STUDY. How Did Humans Become Such a Powerful Species?
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.
4. Natural selection can only act on existing genes and is limited by reproductive capacity.
5. Three common misconceptions about evolution:
a. Fitness is a measure of strength.
b. Organisms develop certain traits because they need them.
c. Evolution works according to some grand plan.
4-3 How do geological 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.
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.
1. Endemic species (those found in only one place) are especially vulnerable.
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, 25–95% of species are lost. There appear to have been at least three and perhaps five
mass extinctions on the earth.
SCIENCE FOCUS: Changing the Genetic Traits of Populations
Artificial selection involves crossbreeding between genetic varieties of the same species to give rise
to populations with desirable traits. Now, scientists can use genetic engineering to produce desirable
traits or eliminate undesirable ones.
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.
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.
B. Some species have broad ecological roles and are termed generalist species.
C. Some species have narrow ecological roles and are termed specialist species.
SCIENCE FOCUS: Scientists Are Searching for the Causes of Amphibian Declines
Herpetologists study amphibians. Some scientists hypothesize viral and fungal diseases are killing
amphibians. Others hypothesize habitat fragmentation, prolonged drought, high levels of UV
radiation, pollution and overhunting.
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.
H. Keystone species have a large affect on maintaining balance within an ecosystem.
1.
CASE STUDY: The American Alligator—A Keystone Species That Almost Went Extinct
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.
1. Foundation species create and enhance habitats that benefit other species.
Key Terms
adaptation
adaptive trait
background extinction
biological diversity
biological evolution
differential reproduction
ecological niche
endemic species
extinction
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fossils
foundation species
generalist species
geographic isolation
indicator species
keystone species
mass extinction
mutations
native species
natural selection
niche
nonnative species
reproductive isolation
specialist species
speciation
species
species diversity
theory of evolution
Chapter 4
Biodiversity and Evolution
Chapter Review Questions and Outlines
Suggested Answers to End of Chapter Questions
Review Questions
1. Core Case Study. Describe the threats to many of the world’s amphibian species (Core Case Study)
and explain why we should avoid hastening the extinction of any amphibian species through our
activities.
 Amphibian’s habitats are changing due to human influence. We should avoid hastening their
extinction because they function as excellent biological indicators, they play important ecological
roles in their communities, and they are a genetic storehouse for pharmaceutical products waiting
to be discovered.
2. Section 4-1. What is the key concept for this section? Define biodiversity (biological diversity) and
list and describe its four major components. What is the importance of biodiversity? Define species?
Summarize the importance of insects. Define and give three examples of biomes. Summarize the
scientific contributions of Edward O. Wilson.
 Key concept: The biodiversity found in genes, species, ecosystems, and ecosystem processes is
vital to sustaining life on earth.
 Biological diversity, or biodiversity, is the variety of the earth’s species, the genes they contain,
the ecosystems in which they live, and the ecosystem processes such as energy flow and nutrient
cycling that sustain all.
 Biodiversity is a vital renewable resource.
 A species is a set of individuals that can mate and produce fertile offspring.
 Insects are pollinators and help sustain life on earth.
 Biomes are large regions with distinct climates and a set of species that are adapted to that
climate. Examples include forests, deserts, and grasslands.
 Edward O. Wilson has acted to educate the public about the importance of preserving
biodiversity.
3. Section 3-2. What are the two key concepts for this section? What is a fossil and why are fossils
important for understanding the history of life? What is biological evolution (or evolution)? State the
theory of evolution. What is natural selection? What is a mutation and what role do mutations play in
evolution by natural selection? What is an adaptation (adaptive trait)? How did humans become such
a powerful species? What are two limits on evolution by natural selection? What are three myths
about evolution through natural selection?
 Key concepts: The scientific theory of evolution explains how life on the earth changes over time
due to changes in the genes of populations. Populations evolve when genes mutate and give some
individuals genetic traits that enhance their abilities to survive and to produce offspring with these
traits (natural selection).
 Fossils are mineralized or petrified replicas of skeletons, bones, teeth, shells, leaves, and seeds, or
impressions of such items found in rocks that help to tell us the history of the earth.
 Biological evolution is the process whereby the earth’s life changes over time through changes in
the genetic characteristics of populations.
 The theory of evolution holds that all species descended from earlier, ancestral species. In other
words, life comes from life.
 Natural selection is the process in which individuals with certain traits are more likely to survive
and reproduce under a particular set of environmental conditions than those without the traits.
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Mutations are random changes in the DNA molecules of a gene in any cell. Mutations can result
from random changes that occur spontaneously within a cell or from exposure to external agents,
such as radioactivity. Mutations can occur in any cell, but only those taking place in genes of
reproductive cells are passed on to offspring. Sometimes such a mutation can result in a new
genetic trait, called a heritable trait, which can be passed from one generation to the next. In this
way, populations develop differences among individuals, including genetic variability.
Adaptation, or adaptive trait, is any heritable trait that improves the ability of an individual
organism to survive and to reproduce at a higher rate than other individuals in a population can
under prevailing environmental conditions.
For natural selection to occur, individuals with adaptive traits must have differential reproduction,
which enables individuals with the trait to leave more offspring than other members of the
population leave.
Human success is attributed to three adaptations: strong opposable thumbs that allow us to grip
and use tools better than the few other animals that have thumbs; an ability to walk upright, which
gives us agility and frees up our hands for many uses; and a complex brain, which has allowed us
to develop many skills, including the ability to use speech to transmit complex ideas.
Two limits to evolution by natural selection include: 1) a change in environmental conditions,
which can lead to such an adaptation only for genetic traits already present in a population’s gene
pool, or for traits resulting from mutations; and 2) even if a beneficial heritable trait is present in a
population, the population’s ability to adapt may be limited by its reproductive capacity.
Three misconceptions:
o “Survival of the fittest” means “survival of the strongest.”
o Organisms develop certain traits because they need them.
o Evolution by natural selection involves some grand plan of nature in which species become
more perfectly adapted.
4. Section 4-3. What is the key concept for this section? Describe how geologic processes can affect
natural selection. How can climate change and catastrophes such as asteroid impacts affect natural
selection?
 Key concept: Tectonic plate movements, volcanic eruptions, earthquakes, and climate change
have shifted wildlife habitats, wiped out large numbers of species, and created opportunities for
the evolution of new species.
 Tectonic plate movements, volcanic eruptions and earthquakes have shifted wildlife habitats,
wiped out large numbers of species, and created opportunities for the evolution of new species.
 Climate change and asteroids have shifted the locations of ecosystems and created opportunities
for evolution.
5. Section 4-4. What are the two key concepts for this section? Define speciation. Distinguish between
geographic isolation and reproductive isolation and explain how they can lead to the formation of a
new species. Distinguish between artificial selection and genetic engineering and give an example of
each.
 Key concepts: As environmental conditions change, the balance between the formation of new
species and the extinction of existing species determines the earth’s biodiversity. Human
activities are decreasing biodiversity by causing the extinction of many species and by destroying
or degrading habitats needed for the development of new species.
 Speciation is when one species splits into two or more different species. For sexually reproducing
organisms, a new species is formed when one population of a species has evolved to the point
where its members no longer can breed and produce fertile offspring with members of another
population that did not change or that evolved in a different way.
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Geographic isolation occurs when different groups of the same population of a species become
physically isolated from one another for a long period of time. For example, part of a population
may migrate in search of food and then begin living as a separate population in another area with
different environmental conditions. Populations can also be separated by a physical barrier (such
as a mountain range, stream, or road), a volcanic eruption, tectonic plate movements, or winds or
flowing water that carry a few individuals to a distant area. In reproductive isolation, mutation
and change by natural selection operate independently in the gene pools of geographically
isolated populations.
Artificial selection enables a change in the genetic characteristics of populations by selecting one
or more desirable genetic traits in the population of a plant or animal such as a type of wheat,
fruit, or dog. Then selective breeding is used to generate populations of the species containing
large numbers of individuals with the desired traits. Genetic engineering is the alteration of an
organism’s genetic material through adding, deleting, or changing segments of its DNA to
produce desirable traits or eliminate undesirable ones. It enables scientists to transfer genes
between different species that would not interbreed in nature. For example, genes from a fish
species can be put into a tomato plant to give it certain properties. Scientists have used genetic
engineering to develop modified crop plants, new drugs, pest-resistant plants, and animals that
grow rapidly.
6. What is extinction? What is an endemic species and why can such a species be vulnerable to
extinction? Distinguish between background extinction rate and mass extinction.
 Extinction is a process in which an entire species ceases to exist (biological extinction) or a
population of a species becomes extinct over a large region, but not globally (local extinction).
 Species that are found in only one area are called endemic species and are especially vulnerable
to extinction because they are unlikely to be able to migrate or adapt in the face of rapidly
changing environmental conditions.
 Throughout most of the earth’s long history, species have disappeared at a low rate, called
background extinction. Mass extinction is a significant rise in extinction rates above the
background level. In such a catastrophic, widespread, and often global event, large groups of
species (25–95% of all species) are wiped out worldwide in a few million years or less.
7. Section 4-5. What is the key concept for this section? Define species diversity and distinguish
between species richness and species evenness. Explain why species-rich ecosystems tend to be
productive and sustainable.
 Key concept: Species diversity is a major component of biodiversity and tends to increase the
sustainability of some ecosystems.
 An important characteristic of a community and the ecosystem to which it belongs is its species
diversity: the number of different species it contains (species richness) combined with the relative
abundance of individuals within each of those species (species evenness).
 A biologically diverse community such as a tropical rain forest or a coral reef with a large
number of different species (high species richness) generally has only a few members of each
species (low species evenness). A single tree in a tropical forest in Panama may house an
estimated 1,700 different beetle species but only a few individuals of each species. In contrast, an
aspen forest community in Canada may have only a few plant species (low species richness) but
large numbers of each species (high species evenness).
 Species diversity is a major component of biodiversity and tends to increase the sustainability of
some ecosystems. Research suggests that species richness affect an ecosystem because plant
productivity is higher in species-rich ecosystems and species richness enhances the stability, or
sustainability of an ecosystem.
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8. Section 4-6. What are the two key concepts for this section? Define and distinguish between an
ecological niche (or niche) and a habitat. Distinguish between generalist species and specialist
species and give an example of each. Why has the fact that the giant panda is a specialist species led
to its classification as an endangered species?
 Key concepts: Each species plays a specific ecological role called its niche. Any given species
may play one or more of four important roles—native, nonnative, indicator, or keystone—in a
particular ecosystem.
 An important principle of ecology is that each species has a specific role to play in the
ecosystems where it is found. Scientists describe the role that a species plays in its ecosystem as
its ecological niche, or simply niche. It is a species’ way of life in a community and includes
everything that affects its survival and reproduction, such as how much water and sunlight it
needs, how much space it requires, and the temperatures it can tolerate. A habitat is the place
where a species lives.
 Generalist species have broad niches. They can live in many different places, eat a variety of
foods, and often tolerate a wide range of environmental conditions. Flies, cockroaches, mice, rats,
white-tailed deer, raccoons, and humans are generalist species.
 Specialist species occupy narrow niches. They may be able to live in only one type of habitat, use
one or a few types of food, or tolerate a narrow range of climatic and other environmental
conditions. For example, tiger salamanders breed only in fishless ponds where their larvae will
not be eaten.
 Giant pandas have a very narrow niche, and therefore are greatly affected by human activities and
climate change.
9. Define and distinguish among native, nonnative, indicator and keystone species and give an example
of each. What major ecological roles do amphibian species play (Core Case Study)? List six factors
that contribute to the threats of extinction for frogs and other amphibians. What are three reasons for
protecting amphibians? Describe the role of the American alligator as a keystone species.
 Native species are those species that normally live and thrive in a particular ecosystem. Other
species that migrate into, or are deliberately or accidentally introduced into, an ecosystem are
called nonnative species, also referred to as invasive, alien, and exotic species. The African bee
would be native to Africa but a nonnative to Brazil. Keystone species’ roles have a large effect on
the types and abundance of other species in an ecosystem. Honeybees are keystone species.
 Species that provide early warnings of damage to a community or an ecosystem are called
indicator species. The presence or absence of trout species in water at temperatures within their
range of tolerance is an indicator of water quality because trout need clean water with high levels
of dissolved oxygen.
 Amphibians help to control insect populations.
 Six factors:
o Habitat loss
o Drought
o Increases in UV radiation
o Parasites
o Viral and fungal diseases
o Pollution
 Three reasons:
o They are indicator species.
o They control insect populations.
o They are a storehouse of pharmaceutical chemicals.
 Birds are excellent indicator species because they are found almost everywhere and are affected
quickly by
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As most American alligators were eliminated from their natural areas in the 1950s, scientists
began pointing out the ecological benefits these animals had been providing to their ecosystems
(such as building water holes, nesting mounds, and feeding sites for other species). Since that
time, they were placed on the endangered species list, and their numbers have increased
dramatically.
10. What are this chapter’s three big ideas? How are ecosystems and the variety of species they contain
related to the three principles of sustainability?
 The three big ideas:
o Populations evolve when genes mutate and give some individuals genetic traits that
enhance their abilities to survive and to produce offspring with these traits (natural
selection).
o Human activities are decreasing the earth’s vital biodiversity by causing the extinction of
species and by disrupting habitats needed for the development of new species.
o Each species plays a specific ecological role (ecological niche) in the ecosystem where it is
found.
 Ecosystems are storehouses of biodiversity that are solar powered and that recycle matter.
Ecosystems are a model for sustainability.
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