1. Historically, island species have tended to become extinct faster than species living on a mainland. Which of the following reasons can be used to explain this phenomenon?

a. Island species have often evolved in the absence of predators and have no natural avoidance strategies.

b. Humans have introduced diseases and competitors to islands, which negatively affects island populations.

c. Island populations are usually smaller than mainland populations.d. All of the above.

The correct answer is d—A. Answer a is incorrect. Island species have often evolved in the absence of

predators and cannot defend against human hunters or other introduced predators such as rats and cats, but this is not the only answer.

The correct answer is d—B. Answer b is incorrect. As humans move around to new areas, they carry germs

and other species with them. These new diseases can rapidly deplete a susceptible population. Introduced species can often outcompete native species and drive their populations to extinction. This, however, is not the only answer.

The correct answer is d—C. Answer c is incorrect. Island populations are usually smaller than mainland

populations and small populations have a higher extinction rate. This, however, is not the only correct answer.

The correct answer is d—All of the above. D. Answer d is correct. All of the preceding factors may play a role in the greater

extinction rate of island species.

Hint: In the past, most extinctions took place on islands. Island species are often unable to defend against predators, have no immunity to introduced diseases, cannot outcompete introduced species, and have smaller population sizes. All of these factors contribute to a higher probability of extinction.

2. An endemic species is—a. one found in many different geographic areasb. one found naturally in just one geographic areac. one found only on islandsd. one that has been introduced to a new geographic area

The correct answer is b—A. Answer a is incorrect. A species that is found in many different geographic areas

is not an endemic species.

The correct answer is b—one found naturally in just one geographic area

B. Answer b is correct. Species that are found in just one geographic area are endemic species.

The correct answer is b—C. Answer c is incorrect. Many island species are endemic, but there are also

mainland endemic species.

The correct answer is b—D. Answer d is incorrect. A species that has been introduced to a new geographic

area is an introduced or exotic species.

Hint: An endemic species is one that is found in just one geographic area. Endemic species, because of their limited ranges, are more prone to extinction.

3. Conservation hotspots are best described as—a. areas with large numbers of endemic species that are disappearing rapidlyb. areas where people are particularly active supporters of biological

diversityc. islands that are experiencing high rates of extinctiond. areas where native species are being replaced with introduced species

The correct answer is a—areas with large numbers of endemic species that are disappearing rapidly

A. Answer a is correct. Hotspots are recognized as areas with large numbers of endemic species that are rapidly being lost.

The correct answer is a—B. Answer b is incorrect. Hotspots are recognized as areas with large numbers of

endemic species that are rapidly being lost.

The correct answer is a—C. Answer c is incorrect. Some hotspots are islands; however, many mainland areas

are also conservation hotspots.

The correct answer is a—D. Answer d is incorrect. Introduced species can contribute to extinction of

endemics but it is not the only factor that results in production of a hotspot.

Hint: Hotspots are areas with a large number of endemic species that are disappearing rapidly. Conservation biologists often focus their efforts on these conservation hotspots.

4.  Biodiversity hotspots—  a. cover 1.4% of the world’s land surface but are home to 35% of extant

terrestrial vertebrate species

b. cover 35% of the world’s land surface but are home to 1.4% of extant terrestrial vertebrate species

c. are found only on islandsd. are found only in the tropics

 The correct answer is a—cover 1.4% of the world’s land surface but are home to 35% of extant terrestrial vertebrate species

A.  Answer a is correct.  Hotspots are so named because they contain a disproportionate diversity of species of organisms, not just vertebrates.

 The correct answer is a—

B.  Answer b is incorrect. Such a level of diversity would be unremarkable. 

The correct answer is a—C.  Answer c is incorrect. Hotspots are scattered around the world, including islands

and continents. 

The correct answer is a— D.  Answer d is incorrect. Hotspots are not limited to tropical climates, even though

such areas are typically high in diversity.  What is unique about hotspots is that their diversity and levels of endemism are unusually high and not limited to areas with typically high diversity (the tropics).

 5. The ability of an intact ecosystem, such as a wetland, to buffer against flooding

and filter pollutants from water is a(n) ________ value of biodiversity.a. direct economicb. indirect economicc. ethical d. aesthetic

The correct answer is b—A. Answer a is incorrect. Direct economic benefits of biodiversity include such

species’ value as food, medicine, clothing, and fuel.

The correct answer is b—indirect economicB. Answer b is correct. Indirect economic benefits of biodiversity include an intact

ecosystem’s ability to buffer against environmental damage.

The correct answer is b—C. Answer c is incorrect. Ethical arguments for the preservation of biodiversity

center on the belief that every species is of value in its own right.

The correct answer is b—D. Answer d is incorrect. Aesthetic values of biodiversity include the enjoyment

humans receive from experiencing plants and animals.

Hint: Intact ecosystems can provide indirect economic values such as maintaining flood waters, cleaning water and air, and preserving soils. These indirect economic values are often of greater benefit than the direct benefits of exploiting individual species within an ecosystem.

6. The economic value of indirect ecosystem services—a. is unlikely to exceed the economic value derived from uses after

ecosystem conversionb. has never been carefully determinedc. can greatly exceed the value derived after ecosystem conversiond. is entirely aesthetic

The correct answer is c—A. Answer a is incorrect. Uses after conversion are often limited and provide returns

that are not sustainable or that do not incorporate all the costs of conversion, including removal of nonrenewable removal of resources and pollution to the environment.

The correct answer is c—B. Answer b is incorrect. Over the last decade both economists and ecologists have

been able to conduct careful studies that estimate the costs and benefits of ecological conversion.

The correct answer is c—can greatly exceed the value derived after ecosystem conversionC. Answer c is correct. In fact, in many cases in which it has been studied and when

the full range of costs and benefits are quantitatively accounted for, the original services of the intact habitat are much more valuable than the short-term gains from conversion.

The correct answer is c—D. Answer d is incorrect. Aesthetic values are but one component; there are many

more including buffering of potentially damaging environmental change (such as, hurricanes), a source of biological resources (such as, pharmaceuticals and agricultural products).

7. The amphibian decline is best described as—a. global disappearance of amphibian populations due to the pervasiveness of

local habitat destructionb. global shrinkage of amphibian populations due to global climate changec. the unexplained disappearance of golden toads in Costa Ricad. none of the above

The correct answer is d—A. Answer a is incorrect. The amphibian decline is not easily attributable to habitat

loss since populations and species are going extinct in many of the most pristine habitats in the world.

The correct answer is d—B. Answer b is incorrect. Although global climate change has been implicated as a

contributing factor, not all changes in population size can be unmistakably attributed to changes in temperature, precipitation, or other indicators of climate change.

The correct answer is d—C. Answer c is incorrect. Golden toads are just one example, though an important

one due to the awareness of a potential problem it helped spark.

The correct answer is d—none of the aboveD. Answer d is correct. The global amphibian decline is attributable to multiple

interacting sources that vary in combination from place to place but which lead to the same results—shrinking population size or extinction outright.

8. Habitat fragmentation can negatively affect populations—a. by restricting gene flow among areas that were previously continuousb. by increasing the relative amount of edge in suitable habitat patchesc. by creating patches that are too small to support a breeding populationd. all of the above

The correct answer is d—A. Answer a is correct. Is not the only correct effect of habitat fragmentation. The

relative importance of genetic limitations in any particular case will derive from a combination of inbreeding effects, drift, and the importance of genetic variation as a response to environmental changes.

The correct answer is d—B. Answer b is correct. It is not the only correct effect of habitat fragmentation.

Edges can increase access of predators or parasites formerly not having access to threatened organisms in the interiors of larger patches.

The correct answer is d—C. Answer c is correct. It is not the only correct effect of habitat fragmentation. If

patches are reduced below a size at which individuals can successfully reproduce, then there will be no recruitment of individuals to offset mortality.

The correct answer is d—all of the aboveD. Answer d is correct. All of the preceding answers are correct.

8. A keystone species is one that—a. has a higher likelihood of extinction than a nonkeystone speciesb. exerts a strong influence on an ecosystem out of proportion to its

abundancec. causes other species to become extinct

d. has a weak influence on an ecosystem

The correct answer is b—A. Answer a is incorrect. Keystone species do not have a higher likelihood of

extinction than nonkeystone species.

The correct answer is b—exerts a strong influence on an ecosystem out of proportion to its abundance

A. Answer b is correct. A keystone species has a strong influence on an ecosystem and the other species that constitute that ecosystem.

The correct answer is b—C. Answer c is incorrect. A keystone species does not cause other species to go

extinct. However, if a keystone species goes extinct it may lead to the extinction of other dependent species.

The correct answer is b—D. Answer d is incorrect. A keystone species has a strong influence on an

ecosystem, not a weak influence.

Hint: Keystone species are species that exert a strong influence on an ecosystem out of proportion to their abundance. Flying foxes are a keystone species because without them many plants are not being pollinated and their seeds are not being dispersed. This has had a major effect on forest ecosystems in places such as Guam.

9. When populations are drastically reduced in size, genetic diversity and heterozygosity—

a. are likely to increase, enhancing the probability of extinctionb. are likely to decrease, enhancing the probability of extinctionc. are usually not factors that influence the probability of extinctiond. automatically respond in a way that protects populations from future

changes

The correct answer is b—A. Answer a is incorrect. Removing individuals at a high rate removes copies of

alleles that may be relatively rare. As the population becomes more and more homogeneous, the heterozygosity of individuals also decreases.

The correct answer is b—are likely to decrease, enhancing the probability of extinctionA. Answer b is correct. Decreased genetic diversity and heterozygosity have been

linked to extinctions of species such as the prairie chicken in the Midwestern United States.

The correct answer is b—C. Answer c is incorrect. Genetic factors and demographic factors are both important

and can interact with one another.

The correct answer is b—D. Answer d is incorrect. Reducing population size reduces genetic variation. With

fewer individuals breeding, there is less chance for reassortment of genes and for new mutations to arise in the population.

10. A captive-breeding program followed by release to the wild—a. is very likely, all by itself, to save a species threatened by extinctionb. is only likely to succeed when genetic variation of wild populations is very

lowc. may be successful when combined with proper regulations and habitat

restorationd. none of the above

The correct answer is c—A. Answer a is incorrect. Captive breeding and release, although successful in some

very important cases (for example, peregrine falcons and the California condor) is fraught with difficulties including the likelihood that damage to native habitat cannot be controlled or reversed and that genetic variation of natural populations targeted for captive-breeding programs often have very low genetic variation.

The correct answer is c—B. Answer b is incorrect. Low genetic diversity reduces the probability of sustaining

a sufficient genetic pool to enable response to new environmental challenges.

The correct answer is c—may be successful when combined with proper regulations and habitat restoration

C. Answer c is correct. Carefully managed plans that address low genetic variation in breeding stocks, habitat restoration, regulations that protect released individuals, and educate the public have the best chance of success. Such efforts are complex, expensive, and only occasionally successful. Nevertheless, we have several examples in which such efforts paid off with very large ecological dividends.

The correct answer is c—D. Answer d is incorrect.

11. Ninety-nine percent of all the species that ever existed have gone extinct— a. serving as evidence that current extinction rates are not higher than normalb. but most of these losses have occurred in the last 400 yearsc. which argues that the world just had too many speciesd. none of the above

The correct answer is d—A. Answer a is incorrect. Extinction rates, estimated over the last few centuries

appear to be on the rise, especially for some taxa (for example, birds). Moreover,

there are very diverse groups (like invertebrates) are so large it is hard to get good estimates. Many studies suggest that extinction rates are elevated over historical and natural levels.

The correct answer is d—B. Answer b is incorrect. The losses have been gradual over the millions of years that

life has existed. Nevertheless, humans have been associated with negative effects on other species, especially large vertebrates.

The correct answer is d—C. Answer c is incorrect. There is no evidence that species diversity is declining

because there are too many species. There is not ecological theory that suggests such a limit on species diversity at the global scale.

The correct answer is d—none of the aboveD. Answer d is correct.

12. To effectively address the biodiversity crisis, the protection of individual species—

a. must be used in concert with a principle of ecosystem management and restoration

b. is a sufficient management approach that merely needs to be expanded to more species

c. has no role to play in addressing the biodiversity crisisd. usually conflicts with the principle of ecosystem management

The correct answer is a—must be used in concert with a principle of ecosystem management and restoration

A. Answer a is correct. Protection of individual species (for example, by the Endangered Species Act) still provides tools needed to avert the extinction of species, but it is no longer the single focus of conservation biologists. As our appreciation of the complexities of species’ roles in ecological systems grows with each new study (consider the examples of keystone species) it is clear that functioning ecosystems need to be the focus of conservation and restoration regulations and efforts.

The correct answer is a—A. Answer b is incorrect. Although inadequate enforcement may thwart progress in

specific protection efforts, protection of individual species does not necessarily address the issues leading to the threats in the first place.

The correct answer is a—C. Answer c is incorrect. As seen in the cases of peregrine falcons and California

condors, targeting individual species can contribute significantly to rescuing them from extinction.

The correct answer is a—D. Answer d is incorrect. A comprehensive approach that targets species within the

framework of their ecological interactions, such that the interactions are the focus of conservation and restoration, holds the greatest promise in addressing the biodiversity crisis. Case studies of the Yellowstone wolves, habitat corridors, and other large-scale conservation efforts that restore ecological functions are strong evidence for the efficacy of such an approach.

Challenge Questions

1. If 99% of the species that ever existed are now extinct, why is there such concern over the extinction rates over the last several centuries?

Answer—Although it is true that extinction is a natural part of the existence of a species, several pieces of evidence suggest that current rates of extinction are much elevated over the natural background level and the disappearance is associated with human activities (which many of the most pronounced extinction events in the history of the Earth were not). It is important to appreciate the length of time over which the estimate of 99% is made. The history of life on Earth extends back billions of years. Certainly, clear patterns of the emergence and extinction of species in the fossil record extend back many hundreds of millions of years. Since the average time of species’ existence is short relative to the great expanse of time over which we can estimate the percentage of species that have disappeared, the perception might be that extinction rates have always been high, when in fact the high number is driven by the great expanse of time of measurement. We have very good evidence that modern extinction rates (over human history) are considerably elevated above background levels. Furthermore, the circumstances of the extinctions may be very different because they are also associated with habitat and resource removal; thus potentially limiting the natural processes that replace extinct species.

2. Ecosystem conversion always has a cost and a benefit. Usually the benefit flows to a segment of society (a business or one group of people, for instance), but the costs are borne by all of society. That is what makes decisions about how and when to convert ecosystems difficult. However, is that a problem unique to conversion of ecosystems in the way we understand it today (for example, the conversion of the mangrove to a shrimp farm)? Are there other examples we can look to for guidance in how to make these decisions?

Answer—The problem is not unique and not new. It represents a classic conflict that is the basic source of societal laws and regulations, especially in the management of resources. For example, whether or not to place air pollution scrubbers on the smoke stacks of coal-fired power plants is precisely the same issue. In this case, it is not ecosystem conversion, per se, but the fact that the businesses that run the power plants benefit from their operation, but the public “owns” and relies on the atmosphere is a conflict between public and private interests. Some of the ways to navigate the dilemma is for society to create regulations to protect the public interest. The problem is difficult

and clearly does not depend solely on economic valuation of the costs and benefits because there can be considerable debate about those estimates. One only has to look at the global climate change problem to suggest how hard it will be to make progress in an expedient manner.

3. There is concern and evidence that amphibian populations are declining worldwide as a consequence of factors acting globally. Given that we know that species extinction is a natural process, how do we determine if there is a global decline that is different from normal species extinction?

Answer—This is not a trivial undertaking, which is why, since the first concerns were raised in the late 1980s, it has taken nearly 15 years to collect evidence showing a decline is likely. Although progress has been made on identifying potential causes, much work remains to be done. Many amphibians are secretive, relatively long-lived, and subject to extreme population fluctuations. Given those facts about their biology, documenting population fluctuations (conducting censuses of the number of individuals in populations) for long periods of time is the only way to ultimately establish the likely fate of populations, and that process is time-consuming and costly.