1. When individuals respond physiologically to an environmental change—
a. natural selection has occurred
b. differences among individuals could lead to evolution by natural selection
c. they cannot respond simultaneously through changes in behavior and
morphology
d. none of the above
The correct answer is b—
A. Answer b is incorrect. A response by an individual occurs within a generation,
whereas natural selection operates across generations based on phenotypic and
genetic variation that has fitness consequences.
The correct answer is b—differences among individuals could lead to evolution by
natural selection
B. Answer b is correct. When individuals vary in their responses to the environment,
then it is possible for there to be fitness effects that might be passed on to
offspring if there is a genetic basis to the response.
The correct answer is b—
C. Answer c is incorrect. Organisms often respond to changes in their environment
in multiple ways simultaneously. There is nothing precluding a suite of responses
to an environmental challenge. For example, when lizards choose a warm site to
bask such that they can raise their body temperatures (behavior), they also often
have the capacity to alter patterns of blood flow to their periphery (vasodilation of
the peripheral capillaries) to speed heating.
The correct answer is b—
D. Answer d is incorrect. One of the choices is correct.
2. Geographic ranges of populations—
a. were static until human disturbance led to extinction and introductions
b. are never affected by the distribution and abundance of predators
c. do not respond to long-term climatic changes
d. none of the above
The correct answer is d—
A. Answer a is incorrect. There are many historical data demonstrating that
organisms often respond to natural environmental changes through modifications
of their geographic range.
The correct answer is d—
B. Answer b is incorrect. Both biotic and abiotic factors can affect the geographic
range of an organism.
The correct answer is d—
C. Answer c is incorrect. Such environmental changes are responsible for the
profound changes in ecological communities over geologic history. For example,
during glacial advance and retreat, whole floras can move up or down in elevation
in response to long-term temperature changes.
The correct answer is d—none of the above
D. Answer d is correct. None of the offered answers is correct.
3. Source–sink metapopulations are distinct from other types of metapopulations
because—
a. exchange of individuals only occurs in the former
b. populations with negative growth rates are a part of the former
c. populations never go extinct in the former
d. all populations eventually go extinct in the former
The correct answer is b—
A. Answer a is incorrect. In all types of metapopulations, exchange of individuals is
a defining characteristic.
The correct answer is b—populations with negative growth rates are of source–sink
metapopulations
B. Answer b is correct. A sink is defined as a subpopulation that cannot sustain itself
in the absence of influx from neighboring (source) populations.
The correct answer is b—
C. Answer c is incorrect. Sink populations can and do go extinct regularly,
sometimes colonized by individuals from source populations.
The correct answer is b—
D. Answer d is incorrect. although extinction is a property of all populations over
time (no population can last forever), the eventual fact of extinction is not a way
to differentiate source–sink dynamics from a regular metapopulation.
4. I would expect the potential for social interactions among individuals to be
maximized when individuals—
a. are randomly distributed in their environment
b. are uniformly distributed in their environment
c. have a clumped distribution in their environment
d. are nonrandomly distributed in their environment
The correct answer is c—
A. Answer a is incorrect. A random spacing of individuals leads to some individuals
being close together and some being far apart.
The correct answer is c—
B. Answer b is incorrect. Especially at low densities, spacing among individuals may
be large reducing the potential for social interactions.
The correct answer is c—have a clumped distribution in their environment
C. Answer c is correct. A clumped distribution is the one most likely to allow groups
of individuals to participate with one another in various kinds of social
interactions.
The correct answer is c—
D. Answer d is incorrect. Even though a uniform distribution is nonrandom (as is a
clumped distribution), only the clumped distribution is the kind of nonrandom
distribution that is likely to maximize social interactions among individuals.
5. When ecologists talk about the cost of reproduction they mean—
a. the reduction in future reproductive output as a consequence of current
reproduction
b. the amount of calories it takes for all the activity used in successful
reproduction
c. the amount of calories contained in eggs or offspring
d. none of the above
The correct answer is a—the reduction in future reproductive output as a consequence of
current reproduction
A. Answer a is correct. The concept of the “cost of reproduction” is how much a
current effort affects future effort, all in terms of reproductive output. It is an
attempt to estimate the value (in terms of fitness) of a given level of effort
compared with future potential effort.
The correct answer is a—
B. Answer b is incorrect. Caloric value of the reproductive products by itself may not
be a good measure of how a current effort will affect a future effort. Imagine an
animal that has access to an unlimited store of energy, a large caloric investment
in a current effort will probably not have the same consequences as an equivalent
caloric investment by an individual that has access to only a limited store of
energy.
The correct answer is a—
C. Answer c is incorrect. It is incorrect because of the reasoning provided above in b.
The correct answer is a—
D. Answer d is incorrect. One of the options is correct.
6. A life history trade-off between clutch size and offspring size—
a. means that as clutch size increases, offspring size increases
b. means that as clutch size increases, offspring size decreases
c. means that as clutch size increases, adult size increases
d. means that as clutch size increases, adult size decreases
The correct answer is b—
A. Answer a is incorrect. If offspring size increased as clutch size increased, that
would be a positive relationship and a trade-off is a negative relationship.
The correct answer is b—means that as clutch size increases, offspring size decreases
B. Answer b is correct. A trade-off refers to a negative relationship. In this case, as
more offspring are produced from a fixed amount of energy, the consequence is
that each one has to be smaller. Imagine a pie; if you want bigger slices, there
will be fewer of them.
The correct answer is b—
C. Answer c is incorrect. A clutch size/offspring size trade-off is not necessarily
related to adult size, increasing or decreasing.
The correct answer is b—
D. Answer d is incorrect. A clutch size/offspring size trade-off is not necessarily
related to adult size, either increasing or decreasing.
7. The difference between exponential and logistic growth rates is—
a. exponential growth depends on birth and death rates and logistic does not
b. in logistic growth, emigration and immigration are unimportant
c. that both are affected by density, but logistic growth is slower
d. that only logistic growth reflects density-dependent effects on births or
deaths
The correct answer is d—
A. Answer a is incorrect. Population growth rate is always a function of birth and
death rates.
The correct answer is d—
B. Answer b is incorrect. Immigration and emigration act just like birth and death for
any population in that the former adds new individuals, and the latter removes
individuals.
The correct answer is d—
C. Answer c is incorrect. Only in logistic growth is the rate of change in size affected
by the density of individuals.
The correct answer is d—that only logistic growth reflects density-dependent effects on
births or deaths
D. Answer d is correct. A population with a larger proportion of older individuals
than younger individuals will most likely experience a negative population growth
(death rate will be higher than birth rate), which will decrease population size.
Hint: Older individuals are postreproductive. A population with a larger proportion
of older individuals than younger individuals will experience negative population
growth. As long as the young cohorts continue to reproduce, the population will
eventually stabilize at a smaller population size.)
8. Humans are an example of an organism with a type I survivorship curve. This
means—
a. mortality rates are highest for younger individuals
b. mortality rates are highest for older individuals
c. mortality rates are constant over the life span of individuals
d. the population growth rate is high
The correct answer is b—
A. Answer a is incorrect. Organisms with a type I survivorship curve show the
highest mortality in the older age classes.
The correct answer is b—mortality rates are highest for older individuals.
B. Answer b is correct. Organisms with a type I survivorship curve show the highest
mortality in the older age classes.
The correct answer is b—
C. Answer c is incorrect. Organisms with a type I survivorship curve show the
highest mortality in the older age classes.
The correct answer is b—
D. Answer d is incorrect. Survivorship curves provide information about survival
rates across age groups and not about growth rates of populations.
Hint: Type I survivorship curves are typical of organisms with higher mortality in
older age classes.
9. According to the Population Reference Bureau (2002), the worldwide intrinsic
rate of human population growth (r) is currently 1.3%. In the United States, r =
0.6%. How will the U.S. population change relative to the world population?
a. The world population will grow, while the population of the United States
will decline.
b. The world population will grow, while the population of the United States
will remain the same.
c. Both the world and the U.S. populations will grow, but the world
population will grow more rapidly.
d. The world population will decline, while the U.S. population will increase.
The correct answer is c—
A. Answer a is incorrect. Both populations exhibit a positive value of r. This means
both populations will increase.
The correct answer is c—
B. Answer b is incorrect. Both populations exhibit a positive value of r. This means
both populations will increase.
The correct answer is c—Both the world and the U.S. populations will grow, but the
world population will grow more rapidly.
C. Answer c is correct. Both populations exhibit a positive value of r. This means
both populations will increase. Because the value of r for the world is larger, the
world will exhibit faster population growth.
The correct answer is c—
D. Answer d is incorrect. Both populations exhibit a positive value of r. This means
both populations will increase.
Hint: The intrinsic rate of population growth (r) = birth rate (b) – death rate (d). Any
time r > 0 a population will increase. The larger the value of r, the faster the rate of
population growth.
10. The logistic population growth model, dN/dt = rN[(K – N)/K], describes a
population’s growth when an upper limit to growth is assumed. As N approaches
(numerically) the value of K—
a. dN/d increases rapidly
b. dN/d approaches 0
c. dN/d increases slowly
d. the population becomes threatened by extinction
The correct answer is b—
A. Answer a is incorrect. The closer the population gets to carrying capacity (K), the
more slowly it grows.
The correct answer is b—dN/d approaches 0
B. Answer b is correct. When N = K the whole right term of the equation is rN * 0,
which of course is equal to 0. That is why K is called the carrying capacity,
because growth rate is 0 at that population size.
The correct answer is b—
C. Answer c is incorrect. As population size (N) increases, the change in population
size (dN/dt) decreases.
The correct answer is b—
D. Answer d is correct. At carrying capacity, the population is as large as it can be,
and therefore, just based on population size, is probably at its most unlikely stage
for extinction.
11. Which of the following is an example of a density-dependent effect on population
growth?
a. An extremely cold winter
b. A tornado
c. An extremely hot summer in which cool burrow retreats are fewer than the
number of individuals in the population
d. A drought
The correct answer is c—
A. Answer a is incorrect. An extremely cold winter is a density-independent effect.
An environmental factor, such as temperature, will normally affect individuals
regardless of population size.
The correct answer is c—
B. Answer b is incorrect. A tornado, as another example of an environmental effect,
will normally affect individuals regardless of population size.
The correct answer is c—An extremely hot summer in which cool burrow retreats are
fewer than the number of individuals in the population
C. Answer c is correct. Although high temperatures are an environmental effect, if
retreats exist, allowing individuals to escape that effect, and there are fewer
retreats available than individuals seeking them, then the consequences will
depend on population density.
The correct answer is c—
D. Answer d is incorrect. As with answer a, An environmental factor will normally
affect individuals regardless of population size.
Hint: Density-dependent effects are factors that change in response to population
size. Density-independent effects are factors that do not change in response to
population size.
Challenge Questions
1. Refer to Figure 55.9.
What are the implications for evolutionary divergence among populations that are
part of a metapopulation versus populations that are independent of other
populations?
Answer—The genetic makeup of isolated populations will change over time based on the
basic mechanisms of evolutionary change; for example, natural selection, mutation,
assortative mating, and drift. These same processes affect the genetic makeup of
populations in a metapopulation, but the outcomes are likely to be much more
complicated. For example, if immigration between a source and a sink population is very
high, then local selection in a sink population may be swamped by the regular flow of
individuals carrying alleles of lower fitness from a source population where natural
selection may not be acting against those alleles; divergence might be slowed or even
stopped under some circumstances. On the other hand, if sinks go through repeated
population declines such that they often are made up of a very small number of
individuals, then they may lose considerable genetic diversity due to drift. If immigration
from source populations is greater than zero but not large, these small populations might
begin to diverge substantially from other populations in the metapopulation due to drift.
The difference is that in the metapopulation, such populations might actually be able to
persist and diverge, rather than just going extinct due to small numbers of individuals and
no ability to be rescued by neighboring sources.
2. Refer to Figure 55.14.
Given a trade-off between current reproductive effort and future reproductive
success (the so-called cost of reproduction), would you expect old individuals to
have the same “optimal” reproductive effort as young individuals?
Answer—The probability that an animal lives to the next year should decline with age
(Note that in Figure 55.11, all the curves decrease with age) so the cost of reproduction
for an old animal would, all else being equal, be lower than for a young animal. The
reason is that the cost of reproduction is measured by changes in fitness. Imagine a very
old animal that has almost no chance in surviving to another reproductive event; it should
spend all its effort on a current reproductive effort since its future success is likely to be
zero anyway.
3. Refer to Figure 55.15.
Because the number of offspring that a parent can produce often trades off with
the size of individual offspring, many circumstances lead to an intermediate
number and size of offspring being favored. If the size of an offspring was
completely unrelated to the quality of that offspring (its chances of surviving until
it reaches reproductive age), would you expect parents to fall on the left or right
side of the x-axis (clutch size)? Explain.
Answer—If offspring size does not affect offspring quality, then it is in the parent’s
interest to produce absolutely as many small offspring as possible. In doing so, it would
be maximizing its fitness by increasing the number of related individuals in the next
generation.
4. Refer to Figure 55.27.
Would increasing the mean generation time have the same kind of effect on
population growth rate as reducing the number of children that an individual
female has over her lifetime? Which effect would have a bigger influence on
population growth rate? Explain.
Answer—By increasing the mean generation time (increasing the age at which an
individual can begin reproducing; age at first reproduction), keeping all else equal, one
would expect that the population growth rate would reduced. That comes simply from
the fact of reducing the number of individuals that are producing offspring in the adult
age classes; lower population birth rates would lead to a reduced population growth rate.
As to which would have a larger influence, that is hard to say. If the change in generation
time (increased age at first reproduction) had an overall larger effect on the total number
of offspring an individual female had than a reduced fecundity at any age, then
population growth rate would probably be more sensitive to the change in generation
time. Under different scenarios, the comparison of these two effects could be come more
complicated, however. Suffice it to say that population growth control can come from
more than one source: fecundity and age at first reproduction.