Bio250 Final Exam Questions with Accurate
Solutions
Q2.16. Pileated Woodpeckers (Dryocopus pileatus) excavate large (>45 cm) cavities in
trees that they use for nests and roosts. Wood Ducks (Aix spons) also build nests in
suitable tree holes, but cannot excavate their own cavities. Consequently, they frequently
use nests of Pileated Woodpeckers. Based on this information, which of the following
statements is correct?
a) Wood Ducks are ecosystem engineers because they nest in cavities built by woodpeckers.
b) Pileated Woodpeckers are ecosystem engineers because they excavate tree cavities
that Wood Ducks use to build their nests.
c) Pileated Woodpeckers are ecosystem engineers because they excavate tree cavities to
build their own nests.
d) Neither species is an ecosystem engineer by virtue of their nesting habit.
b
Q2.17. Which of the following statements about trophic cascades is TRUE?
a) A trophic cascade occurs when predation limits herbivore abundance, and plant population
sizes are reduced.
b) A trophic cascade occurs when a predator is removed, allowing plants to expand,
which then limits herbivores.
c) In a trophic cascade, plant abundance depends on the number of trophic levels in the
,community.
d) A behavioral cascade, which often involves the perception of predation risk, is not a
type of trophic cascade.
c
Q3.3. Many community ecologists are concerned about the effects of habitat fragmentation.
In particular they worry that clear-cutting of old growth forests will produce small, isolated
forest patches and that species will be lost from these smaller patches because small
patches cannot support as long a food chain as bigger patches. This concern is based on
which of the following hypotheses discussed in this chapter?
a) The productivity hypothesis
b) The ecosystem-size hypothesis
c) The exploitation ecosystem hypothesis
d) HSS's the 'world is green' hypothesis
b
Q3.4. A wildlife biologist has adopted a number of techniques to protect the Willow
Flycatcher, a bird that often nests and feeds in willows. Some techniques reflect top-down
while some reflect bottom-up control. Which of the following approaches demonstrates
her understanding of how top-down forces affect community dynamics?
a) The biologist attempts to increase food availability by reintroducing beaver. She
hypothesizes that beaver will raise the water table, stimulating the growth of willow,
which will result in an increase in insect abundance, giving flycatchers more food.
,b) Willow Flycatchers can lose eggs to squirrels, weasels, and other predators. The
biologist attempts to protect nests by putting metal collars around the base of the willows
that keep ground predators from climbing up to reach the nests.
c) Both approaches rely on top-down forces.
d) Neither approach relies on top-down forces.
b
Q4.14. Recall that in the big Yellowstone fires, lodgepole pines burned and then grew back
within several decades. With respect to fire, are lodgepole pines resistant and/or resilient?
a) Lodgepole pines are resistant.
b) Lodgepole pines are resilient.
c) Lodgepole pines are both resistant and resilient.
d) Lodgepole pines are neither resistant or resilient.
b
Q4.15. Redwood trees (Sequoia sempervirens) have more biomass than any other plant
species in western redwood forests. They greatly impact the other plant and animal species
that live in these forests. If removed, most understory plants and their associated
herbivores could not survive. Are redwood trees keystone species? Why or why not?
a) Yes, the redwood tree is a keystone species because it has a large impact on
most understory plants in the community.
b) Yes, the redwood tree is a keystone species because its removal would result in the loss of
, herbivores in the community.
c) No, the redwood tree is not a keystone species because its proportional biomass is high.
d) No, the redwood tree is not a keystone species because its impact on the community
isn't much greater than that of other species.
c
Q4.16. Imagine a community with a single predator, two herbivores, and four primary producers
(7 species total). How many food web links are theoretically possible? That is, how many links
are possible if each species is able to feed on every species in the community?
49
Q4.17. Imagine again this hypothetical community with a single predator, two
herbivores, and five primary producers. Assume the following:
(1) The predator is a pure carnivore, feeding on both herbivore species but no plants.
(2) Each herbivore species specializes on a single plant species. (This means some plants
are not consumed.)
(3) The plant species do not feed on other organisms.
(4) There is no cannibalism.
Use this information to calculate the connectance of the system. (Hint: To answer this, you
first need to calculate the number of links in this community, which is most easily done if
you sketch the food web.)
0.062
Q4.18. The following diagrams depict food webs for three different communities, all of
which have 10 species and 4 trophic levels. Based on just the information indicated in the
diagrams, which of the three communities is most likely to be stable?
Solutions
Q2.16. Pileated Woodpeckers (Dryocopus pileatus) excavate large (>45 cm) cavities in
trees that they use for nests and roosts. Wood Ducks (Aix spons) also build nests in
suitable tree holes, but cannot excavate their own cavities. Consequently, they frequently
use nests of Pileated Woodpeckers. Based on this information, which of the following
statements is correct?
a) Wood Ducks are ecosystem engineers because they nest in cavities built by woodpeckers.
b) Pileated Woodpeckers are ecosystem engineers because they excavate tree cavities
that Wood Ducks use to build their nests.
c) Pileated Woodpeckers are ecosystem engineers because they excavate tree cavities to
build their own nests.
d) Neither species is an ecosystem engineer by virtue of their nesting habit.
b
Q2.17. Which of the following statements about trophic cascades is TRUE?
a) A trophic cascade occurs when predation limits herbivore abundance, and plant population
sizes are reduced.
b) A trophic cascade occurs when a predator is removed, allowing plants to expand,
which then limits herbivores.
c) In a trophic cascade, plant abundance depends on the number of trophic levels in the
,community.
d) A behavioral cascade, which often involves the perception of predation risk, is not a
type of trophic cascade.
c
Q3.3. Many community ecologists are concerned about the effects of habitat fragmentation.
In particular they worry that clear-cutting of old growth forests will produce small, isolated
forest patches and that species will be lost from these smaller patches because small
patches cannot support as long a food chain as bigger patches. This concern is based on
which of the following hypotheses discussed in this chapter?
a) The productivity hypothesis
b) The ecosystem-size hypothesis
c) The exploitation ecosystem hypothesis
d) HSS's the 'world is green' hypothesis
b
Q3.4. A wildlife biologist has adopted a number of techniques to protect the Willow
Flycatcher, a bird that often nests and feeds in willows. Some techniques reflect top-down
while some reflect bottom-up control. Which of the following approaches demonstrates
her understanding of how top-down forces affect community dynamics?
a) The biologist attempts to increase food availability by reintroducing beaver. She
hypothesizes that beaver will raise the water table, stimulating the growth of willow,
which will result in an increase in insect abundance, giving flycatchers more food.
,b) Willow Flycatchers can lose eggs to squirrels, weasels, and other predators. The
biologist attempts to protect nests by putting metal collars around the base of the willows
that keep ground predators from climbing up to reach the nests.
c) Both approaches rely on top-down forces.
d) Neither approach relies on top-down forces.
b
Q4.14. Recall that in the big Yellowstone fires, lodgepole pines burned and then grew back
within several decades. With respect to fire, are lodgepole pines resistant and/or resilient?
a) Lodgepole pines are resistant.
b) Lodgepole pines are resilient.
c) Lodgepole pines are both resistant and resilient.
d) Lodgepole pines are neither resistant or resilient.
b
Q4.15. Redwood trees (Sequoia sempervirens) have more biomass than any other plant
species in western redwood forests. They greatly impact the other plant and animal species
that live in these forests. If removed, most understory plants and their associated
herbivores could not survive. Are redwood trees keystone species? Why or why not?
a) Yes, the redwood tree is a keystone species because it has a large impact on
most understory plants in the community.
b) Yes, the redwood tree is a keystone species because its removal would result in the loss of
, herbivores in the community.
c) No, the redwood tree is not a keystone species because its proportional biomass is high.
d) No, the redwood tree is not a keystone species because its impact on the community
isn't much greater than that of other species.
c
Q4.16. Imagine a community with a single predator, two herbivores, and four primary producers
(7 species total). How many food web links are theoretically possible? That is, how many links
are possible if each species is able to feed on every species in the community?
49
Q4.17. Imagine again this hypothetical community with a single predator, two
herbivores, and five primary producers. Assume the following:
(1) The predator is a pure carnivore, feeding on both herbivore species but no plants.
(2) Each herbivore species specializes on a single plant species. (This means some plants
are not consumed.)
(3) The plant species do not feed on other organisms.
(4) There is no cannibalism.
Use this information to calculate the connectance of the system. (Hint: To answer this, you
first need to calculate the number of links in this community, which is most easily done if
you sketch the food web.)
0.062
Q4.18. The following diagrams depict food webs for three different communities, all of
which have 10 species and 4 trophic levels. Based on just the information indicated in the
diagrams, which of the three communities is most likely to be stable?
