Chapter 15: Temporal and Spatial Dynamics of Populations
Topic: temporal and spatial dynamics of... Difficulty: easy
1. Every four years, lemmings make a suicidal rush to the sea in an altruistic behavior that reduces
population density.
A) true B) false
Answer: B
Topic: temporal and spatial dynamics of... Difficulty: easy
2. Sheep and algae differ markedly in volatility of population size in the face of environmental
fluctuations. Why?
A) Sheep are larger and more complex, and thus have greater homeostatic resistance to
physiological effects of environmental change.
B) Sheep are longer-lived, and their populations consist of individuals born over a long period.
This evens out effects on population size of short-term fluctuations in birth rate.
C) Both A and B contribute to this difference.
D) Neither A nor B contributes to this difference.
Answer: C
Topic: temporal and spatial dynamics of... Difficulty: easy
3. Long-term records from trapping of various animals from gyrfalcons to snowshoe hares have
revealed:
A) remarkable stability of these populations.
B) chaotic behavior of these populations.
C) pronounced and regular population cycles.
D) none of the above.
Answer: C
Topic: population cycles Difficulty: easy
4. Research has shown that 11-year cycles in abundance of snowshoe hare populations are caused
by sunspot cycles.
A) true B) false
Answer: B
Topic: population cycles Difficulty: easy
5. Who first made the existence of regular population cycles known to the scientific community?
A) Charles Darwin
C) A.J. Nicholson
B) Charles Elton
D) Danish biologists in the 18th century
Answer: B
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Chapter 15: Temporal and Spatial Dynamics of Populations
Topic: population cycles Difficulty: easy
6. What is the best known example of parallel population fluctuations in predators and their prey?
A) sheep blowflies and sheep from the research of A.J. Nicholson
B) gyrfalcons and lemmings from the research of 18th-century Danish biologists
C) Daphnia and Bosmina from the research of Goulden et al.
D) lynx and snowshoe hares from records of the Hudson Bay Company
Answer: D
Topic: temporal variation and age structure Difficulty: easy
7. A 400-year record of tree recruitment in a virgin stand of timber at Heart's Content,
Pennsylvania, showed that recruitment of most species was:
A) continuous throughout the record.
B) sporadic, usually associated with disturbance.
C) nonexistent.
Answer: B
Topic: temporal and spatial dynamics of... Difficulty: easy
8. Natural populations fluctuate through time. One of the forces causing variation in population
size is variation in the physical environment, which can have both direct and indirect effects on
populations. Variation in population size linked to environmental fluctuation (aside from daily,
lunar, and seasonal cycles) is likely to be:
A) irregular, perhaps even random B) periodic C) Neither of the above.
Answer: A
Topic: temporal and spatial dynamics of... Difficulty: easy
9. Natural populations fluctuate through time. Inherent dynamic properties cause variations in
population size. Variation in population size linked to such properties is likely to be:
A) irregular, perhaps even random. B) periodic. C) Neither of the above.
Answer: B
Topic: population cycles Difficulty: easy
10. The intrinsic population attribute that appears to be responsible for regular cycling of natural
populations is:
A) a very large population (more than 1.6K).
B) a very small population (less than 0.37K).
C) asymmetry of the sex ratio.
D) a time delay in the response of birth and death rates to changes in the environment.
Answer: D
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Chapter 15: Temporal and Spatial Dynamics of Populations
Topic: population cycles Difficulty: moderate
11. In a discrete-time population model with an intrinsic rate of natural increase (r) less than 1, the
population size will exhibit:
A) stability.
B) damped oscillations around carrying capacity.
C) stable oscillations around carrying capacity.
D) chaotic behavior.
Answer: A
Topic: population cycles Difficulty: moderate
12. In a discrete-time population model with an intrinsic rate of natural increase (r) between 1 and 2,
the population size will exhibit:
A) stability.
B) damped oscillations around carrying capacity.
C) stable oscillations around carrying capacity.
D) chaotic behavior.
Answer: B
Topic: population cycles Difficulty: moderate
13. In a discrete-time population model with an intrinsic rate of natural increase (r) much greater
than 2, the population size will exhibit:
A) stability.
B) damped oscillations around carrying capacity.
C) stable oscillations around carrying capacity.
D) chaotic behavior.
Answer: D
Topic: population cycles Difficulty: easy
14. Stable oscillations of a population about its long-term carrying capacity are called:
A) damped oscillations.
C) limit cycles.
B) "bouncy" oscillations.
D) chaotic behavior.
Answer: C
Topic: population cycles Difficulty: hard
15. Several moth populations are exhibiting limit cycles described by continuous-time models with
values for r (intrinsic rate of natural increase) and  (time delay) shown below. Which of these
populations has its maximum size (N) the largest multiple of its carrying capacity (K)?
A) moth A: r = 0.2 and  = 8
D) moth D: r = 0.3 and  = 8
B) moth B: r = 0.2 and  = 12
E) moth E: r = 0.3 and  = 10
C) moth C: r = 0.2 and  = 16
F) moth F: r = 0.3 and  = 12
Answer: F
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Chapter 15: Temporal and Spatial Dynamics of Populations
Topic: population cycles Difficulty: hard
16. Several fish populations are described by continuous-time models with values for r (intrinsic rate
of natural increase) and  (time delay) shown below. Which of these populations will exhibit
damped oscillations?
A) fish A: r = 0.2 and  = 7
D) fish D: r = 0.3 and  = 7
B) fish B: r = 0.2 and  = 9
E) fish E: r = 0.3 and  = 9
C) fish C: r = 0.2 and  = 11
F) fish F: r = 0.3 and  = 11
Answer: A
Topic: population cycles Difficulty: hard
17. In Nicholson's experiments with sheep blowflies, stable limit cycles were observed for adults
when:
A) both larvae and adults were provided unlimited food.
B) larvae were provided a limited food supply while adults were provided unlimited food.
C) larvae were provided unlimited food while adults were provided a limited food supply.
D) both larvae and adults were provided a limited food supply.
Answer: B
Topic: population cycles Difficulty: moderate
18. What did Nicholson determine to be the cause of population cycles in his culture of sheep
blowflies?
A) Density-dependent effects of crowding did not affect mortality rates (and egg production) of
adults immediately.
B) Density-dependent effects of crowding affected mortality rates of adults (and egg
production) immediately.
Answer: A
Topic: population cycles Difficulty: hard
19. Nicholson was able to eliminate population fluctuations in sheep blowflies by changing his
experimental conditions such that:
A) both larvae and adults were provided unlimited food.
B) larvae were provided a limited food supply while adults were provided unlimited food.
C) larvae were provided unlimited food while adults were provided a limited food supply.
D) both larvae and adults were provided a limited food supply.
Answer: D
Topic: metapopulations Difficulty: easy
20. Various processes contribute to the dynamics of metapopulations. One process is the growth and
regulation of subpopulations within patches. What other process(es) are involved?
A) colonization to form new subpopulations
B) extinction of established subpopulations
C) both of the above
D) none of the above
Answer: C
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Chapter 15: Temporal and Spatial Dynamics of Populations
Topic: metapopulations Difficulty: easy
21. What happens to a metapopulation when there is a high rate of migration between its
subpopulations?
A) It goes extinct.
B) Its size remains constant.
C) It grows exponentially.
D) It behaves like a single large population.
Answer: D
Topic: metapopulations Difficulty: hard
22. A metapopulation has an extinction rate, e, of 0.125 and a colonization rate, c, of 0.1. What is
the ultimate fate of this metapopulation, according to the basic model of metapopulation
dynamics, H = 1  e/c?
A) The metapopulation will undergo stable limit cycles.
B) The metapopulation will remain at carrying capacity indefinitely.
C) The metapopulation will decline for a while, then remain at its new carrying capacity
indefinitely.
D) The entire metapopulation will go extinct.
Answer: D
Topic: metapopulations Difficulty: easy
23. Joop Ouborg studied metapopulation dynamics of plant species growing in 143 patches of dry
grassland along the Ijssel and Rhine Rivers. When he compared the presence/absence of
subpopulations in 1956 and again in 1988, he found that:
A) all populations present in 1956 were also present in 1988, regardless of species.
B) some populations present in 1956 were absent in 1988, the percentage loss varying by
species.
C) all populations present in 1956 were extinct in 1988, regardless of species.
Answer: B
Topic: metapopulations Difficulty: moderate
24. When we consider Ouborg's study of plant metapopulations in patches of dry grassland, it is
tempting to consider a subpopulation present in 1956 and 1988 as continually present. Is this
necessarily true?
A) Yes, if the subpopulation was present in both years, it must have occupied the patch
continuously.
B) No, it is possible that the subpopulation may have gone extinct and have been reestablished
during the interval between 1956 and 1988.
Answer: B
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Chapter 15: Temporal and Spatial Dynamics of Populations
Topic: metapopulations Difficulty: moderate
25. When Joop Ouborg examined a set of subpopulations present in 1956 and compared it with those
that were persistent in 1988 with those that were extinct in 1988, he found that:
A) persistent subpopulations tended to contain more individuals in 1956 than extinct ones.
B) persistent subpopulations tended to be closer to other occupied patches than extinct ones.
C) both of the above
Answer: C
Topic: rescue effect Difficulty: moderate
26. The rescue effect can:
A) keep declining subpopulations from dwindling to small numbers and eventual extinction.
B) only work if there is some migration between subpopulations.
C) increase the survival of subpopulations in the presence of more numerous neighboring
subpopulations.
D) all of the above
Answer: D
Topic: rescue effect Difficulty: hard
27. How does a metapopulation model incorporating a rescue effect differ from a model without
one?
A) The rate of extinction, e, is related to the proportion of patches occupied.
B) The rate of extinction is set to 0.
C) The rate of extinction is set equal to the rate of colonization.
D) None of the above is correct.
Answer: A
Topic: stochastic processes Difficulty: moderate
28. The 20 female adults in a small population each has a probability of 0.5 of producing a single
female offspring each year and a probability of 0.5 of producing no offspring. How many female
offspring will be produced each year?
A) no offspring, because a female cannot produce 0.5 offspring
B) exactly 10 offspring per year
C) 10 offspring per year on average, with some variation around this average
D) exactly 20 offspring per year
Answer: C
Topic: stochastic extinction of small... Difficulty: moderate
29. In a simple case, one in which birth and death rates (b and d) are equal and the average change in
population size is zero, the probability of population extinction decreases with:
A) increasing population size B) larger b and d C) time D) all of the above
Answer: A
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Chapter 15: Temporal and Spatial Dynamics of Populations
Topic: stochastic extinction of small... Difficulty: moderate
30. Are density-independent stochastic models relevant to natural populations, given that birth and
death rates in these models do not change with respect to population density?
A) yes B) no
Answer: A
Use the following to answer questions 31-37:
You are a fish specialist in charge of the tropical fish department of a large pet shop. One of your
responsibilities is to ensure a steady supply of live water fleas, Daphnia, for customers who prefer
feeding live food to their tropical fish. Daphnia are Cladocerans, small aquatic invertebrates often used
as live food for fish. Your Daphnia are maintained in a large temperature-controlled tank and fed a diet
of green algae maintained in another culture tank. Keeping a steady supply of Daphnia for your
customers has proven to be an elusive goal, however. Despite maintaining a constant temperature
(25°C) and providing a constant supply of algae, you find that the Daphnia population cycles
dramatically. On some days there are far more Daphnia than needed to meet customer demand (you've
estimated as many as 7400 Daphnia in your culture). On other days, there are so few Daphnia available
that you must turn away customers or risk completely depleting your stock. Population crashes are
preceded by a large buildup of adults, which live 810 days under crowded conditions. Little
reproduction occurs during population highs, and the population declines rapidly as the adults die off.
The population cycling is notably regular, with a period between population peaks of 40 days. Intrigued
by your cycling Daphnia culture, you notify your customers that they will have to rely for a time on
frozen Daphnia while you conduct some experiments.
Topic: population cycles Difficulty: moderate
31. Suspecting that your Daphnia culture may be fluctuating because of varying environmental
conditions, you first search for some condition in your shop that also cycles on a period of 40
days. You monitor the Daphnia tank especially carefully, checking for cycles of light,
temperature, water quality, etc. You find that all these conditions are remarkably constant, and
thus an environmental cause for the Daphnia cycles seems unlikely. Should you be surprised?
Why?
Answer: No. Although population fluctuations may have direct or indirect environmental causes,
environmental fluctuations in nature are typically irregular and the resulting population
fluctuations are thus also irregular. You also seem to have eliminated the possibility of a more
regular environmental fluctuation related, perhaps, to mechanical systems in your shop. What
remains as a potential cause of cycling of your Daphnia culture is some intrinsic dynamic
property of the culture itself.
Topic: population cycles Difficulty: moderate
32. Suspecting an intrinsic biological cause of the Daphnia population cycles, you call in a friend
skilled in modeling population dynamics. Your friend suggests that the cycles are driven by a
time delay in the response of the Daphnia to changes in their environment, notably resource
abundance or scarcity. Your friend shows you how to estimate this time delay, , for your
population. How do you estimate this delay and what is your estimate?
Answer: The period of a population cycle caused by a time delay is typically between 4 and 5.
Given a period of 40 days for your culture, you conclude that the time delay, , is 810 days.
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Chapter 15: Temporal and Spatial Dynamics of Populations
Topic: population cycles Difficulty: hard
33. Through some careful analyses of population growth of Daphnia introduced to a resource-rich
environment, you determine r, the intrinsic rate of increase, to be 0.2 per capita per day. Your
friend then concludes that the undamped cyclic behavior of your Daphnia population is to be
expected. Why does your friend conclude this?
Answer: Work with continuous-time models has shown that populations exhibit limit cycles
when the product r is greater than /2, about 1.6. In your case, the product r is somewhere
between 1.6 and 2.0, sufficiently large to generate the limit cycles observed.
Topic: population cycles Difficulty: hard
34. You are curious as to the underlying cause of the Daphnia population fluctuations observed.
What do you and your knowledgeable friend speculate? (Hint: Consider an example presented
in the text.)
Answer: Your friend is familiar with research conducted by Pratt, in which laboratory cultures of
Daphnia magna maintained at 25°C also cycled, with a period of about 60 days. In the case of
Pratt's work, the population overshot its carrying capacity because adults survived well under
crowded conditions. As the population of Daphnia magna grew, reproduction dropped off, but
mature adults lived, on average, about 10 days. As the remaining young matured, the population
remained high, even in the absence of further reproduction. As adults began to die, reproduction
did not rebound quickly because most of the remaining adults were senescent and
nonreproductive. A population crash resulted, and it took a while for the population to begin
growing rapidly to initiate a new cycle. With slight modification (your periodicity is 40 days),
this scenario seems to fit your population well. The key to time delay in the Daphnia magna
work was the period of adult survival at high densities, about 10 days. Adult survival under
crowded conditions in your culture tank is 810 days, exactly the same as the time delay in your
population.
Topic: population cycles Difficulty: hard
35. Knowing r and  for your Daphnia population, you wonder just how much the culture has been
overshooting the long-term carrying capacity of the culture tank. What is your estimate of the
tank's carrying capacity?
Answer: For populations exhibiting limit cycles, the maximum population is typically Ker.
Taking your higher estimate of r of 2.0, the maximum population should be about Ke2, or 7.4
times K. With a maximum observed population of about 7400, K should be about 1000.
Topic: population cycles Difficulty: hard
36. Your friend suggests lowering the temperature of the culture tank in an attempt to maintain the
Daphnia culture at a more constant level. You try lowering the tank temperature from 25°C to
18°C and you discover that the cycling stops. The population shows a bit of damped oscillation,
then settles into a constant population level at carrying capacity. How did changing the
temperature eliminate cycling? (Hint: Refer to Figure 15.12 and associated discussion in the
text.)
Answer: Once again, you turn to the research of Pratt on Daphnia magna for clues. At the lower
temperature, Pratt found enhanced life span as well as the ability of individuals to give birth even
at high densities. The result was greater overlap of generations, leading to a smoother approach
to carrying capacity without the boom-or-bust behavior seen at the higher temperature.
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Chapter 15: Temporal and Spatial Dynamics of Populations
Topic: population cycles Difficulty: hard
37. Although perhaps not a practical suggestion, your friend wonders if you've ever considered
culturing a smaller, related Cladoceran, Bosmina, instead of Daphnia, as a solution to your
problem with population cycling. Why would culturing Bosmina reduce the likelihood of
population cycling in your cultures?
Answer: By storing fairly large amounts of energy in the form of oil droplets, Daphnia can
persist when food supplies are reduced, permitting populations to overshoot carrying capacity for
a time until the inevitable population crash occurs. The key to population cycling appears to be
the time delay in response of Daphnia to deteriorating conditions permitted by their storage of
energy. Indeed, time delays of some sort appear central to the occurrence of most regular
population cycles. The smaller Bosmina store less energy in the form of oil droplets than
Daphnia. They are thus more prone to starving when food becomes limiting. This lessens the
period of adult survival under crowed conditions, shortening the time delay inherent in the
Bosmina population. With a shorter time delay, Bosmina is much less likely to exhibit limit
cycles. In one study, Bosmina was shown to exhibit damped oscillations under conditions that
led to population cycles in Daphnia.
Topic: size and extinction of natural... Difficulty: easy
38. In a comparative analysis of species lists for birds of the southern California Channel Islands,
larger islands with larger breeding populations suffered __________ extinctions between 1917
and 1968 than smaller islands with smaller breeding populations.
Answer: fewer
Topic: population cycles Difficulty: easy
39. Population fluctuations that take on very complex and unpredictable forms are referred to as
__________.
Answer: chaotic
Topic: population cycles Difficulty: easy
40. Demonstration of population cycling in __________-time models requires the use of a time
delay term, .
Answer: continuous
Topic: metapopulations Difficulty: easy
41. The individuals of a species that live in one of several habitat patches constitute a __________.
Answer: subpopulation
Topic: stochastic processes Difficulty: easy
42. Events that strongly affect all individuals in the population, causing reproductive failure or a
high mortality, are called __________.
Answer: catastrophes
Topic: stochastic processes Difficulty: easy
43. Processes that are influenced by chance events are referred to as __________ processes.
Answer: stochastic
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Chapter 15: Temporal and Spatial Dynamics of Populations
Topic: stochastic processes Difficulty: easy
44. Stochastic extinction becomes increasingly likely as populations become __________.
Answer: smaller
Topic: metapopulations Difficulty: easy
45. Managers of natural areas are increasingly looking to habitat __________ as one way to ensure
migration of individuals among habitat fragments.
Answer: corridors
Topic: population cycles Difficulty: moderate
46. Discrete-time and continuous-time population growth models both show a variety of behaviors
that can include gradual approach to carrying capacity, damped oscillation, stable limit cycles,
and (in the case of discrete-time models) chaotic behavior. Which of these situations actually
results is dependent on the values of certain parameters in the models. How do the discrete-time
and continuous-time models differ in their dependence on these parameters?
Answer: Discrete-time models have an inherent time delay and are thus dependent only on the
value of r, the intrinsic rate of increase, for their behavior. Continuous-time models do not have
an inherent time delay and thus depend on both r and an explicit time delay, , combined into a
single term r.
Topic: metapopulation dynamics Difficulty: moderate
47. What is the basic model of metapopulation dynamics and what factors determine the level of
patch occupancy?
Answer: In the basic model of metapopulation dynamics, the metapopulation attains equilibrium
(i.e., a stable proportion of habitat patches occupied) as described by H = 1  e/c, where H is the
fraction of patches occupied by subpopulations, and e and c are the rates of extinction and
colonization, respectively. Both e and c determine the patch occupancy rate, which ranges from
0 (metapopulation extinction) when e is greater than or equal to c, to 1 (all patches occupied)
when e = 0. For values of e/c between 0 and 1, the metapopulation exists as a changing mosaic
of an equilibrium number of occupied patches.
Topic: metapopulation dynamics Difficulty: easy
48. How does patch size affect the probability of a patch supporting a subpopulation within a
metapopulation? Explain.
Answer: Larger patches are more likely to support a subpopulation at any time than smaller
patches. Smaller subpopulations are far more likely to undergo stochastic extinction than larger
ones.
Topic: metapopulation dynamics Difficulty: moderate
49. What is the rescue effect and how does it affect metapopulation dynamics?
Answer: The rescue effect describes the situation in which the likelihood of extinction of any
subpopulation is not constant but rather a function of the fraction of patches occupied within the
metapopulation. With greater occupancy of patches, there are more numerous sources of
migrants ("rescuers") moving from source to sink subpopulations. This translates into reduced
likelihood of extinction. The overall effect is the introduction of a positive density dependence
among subpopulations.
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Chapter 15: Temporal and Spatial Dynamics of Populations
Topic: deterministic and stochastic models Difficulty: moderate
50. Compare and contrast deterministic and stochastic population models. Also compare the
predictions of deterministic and stochastic population models for the situation in which per
capita birth and death rates are equal.
Answer: Deterministic population models have predictable outcomes (with the exception of the
chaotic behavior of discrete-time models with large r). Stochastic models are similar in form,
but incorporate chance events (stochastic processes) and thus do not have predictable outcomes.
For b = d, a deterministic model will predict a population that is unvarying in size. Under the
same constraint, a stochastic model guarantees only that the average change in population size is
zero. The population may fluctuate in size and has a finite probability (which can be computed)
of reaching a size of 0 (i.e., going extinct).
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