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 areas
b. one found naturally in just one geographic area
c. one found only on islands
d. 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 rapidly
b. areas where people are particularly active supporters of biological
diversity
c. islands that are experiencing high rates of extinction
d. 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 islands
d. 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 economic
b. indirect economic
c. 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 economic
B. 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 conversion
b. has never been carefully determined
c. can greatly exceed the value derived after ecosystem conversion
d. 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 conversion
C. 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 destruction
b. global shrinkage of amphibian populations due to global climate change
c. the unexplained disappearance of golden toads in Costa Rica
d. 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 above
D. 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 continuous
b. by increasing the relative amount of edge in suitable habitat patches
c. by creating patches that are too small to support a breeding population
d. 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 above
D. 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 species
b. exerts a strong influence on an ecosystem out of proportion to its
abundance
c. 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 extinction
b. are likely to decrease, enhancing the probability of extinction
c. are usually not factors that influence the probability of extinction
d. 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 extinction
A. 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 extinction
b. is only likely to succeed when genetic variation of wild populations is very
low
c. may be successful when combined with proper regulations and habitat
restoration
d. 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 normal
b. but most of these losses have occurred in the last 400 years
c. which argues that the world just had too many species
d. 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 above
D. 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 crisis
d. 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.