A36fiffAnswers
Figure 20.5
Q1: What species eats the coyote?
A1: The gray wolf.
Q2: What species does the coyote eat?
A2: The vole, the snowshoe hare, berries, the pronghorn,
and the elk.
Q3: What do you think would happen to a community that lost its
coyotes?
A3: The snowshoe hare and the vole would overeat the grasses and
other plants, and once those food sources were destroyed, their
unavailability would cause the snowshoe hare and vole populations
to crash.
Figure 20.6
Q1: Where do producers acquire the energy they need to perform
their function in the food chain?
A1: From the sun. In combination with CO 2 and water, they
produce glucose through photosynthesis.
Q2: Why are producers necessary for life on Earth?
A2: Without producers, there would be no influx of energy
into Earth’s biosphere—no energy source for consumers to
acquire.
Q3: Given the lower abundance of producers in desert regions,
compared to tropical rainforests, what would you predict about the
abundance of consumers in the two environments?
A3: Consumer species would be less abundant in deserts than in
rainforests.
Figure 20.7
Q1: When did wolves begin to be seen again in Yellowstone?
A1: In the mid- to late 1980s.
Q2: What was the highest number of wolves observed in
Yellowstone? In what year did that occur?
A2: About 174 individuals, in 2003.
Q3: Why did it take a few years after the reintroduction of
wolves for the aspen population to increase, as well as the beavers
and bears?
A3: Each individual parent plant can produce only a certain
number of offspring at a time, and then those offspring have to
reach maturity before they themselves can reproduce.
Figure 20.8
Q1: What might happen to an anemone without a resident
clownfish?
A1: An anemone unaccompanied by clownfish, and therefore
unprotected from anemone-eating fish, could be grazed
extensively and be unable to support its growth needs without the
nutrients in the clownfish excrement.
Q2: What would happen to a clownfish that did not produce a
mucous coating?
A2: It would be stung by the anemone’s tentacles, so the mutualism
would fall apart.Q3: In the example of mutualism given in the text, what would
happen if ticks were no longer able to feed on bison?A3: There would be nothing for the birds to eat off of the bison,
and no reason for the bison to allow the birds on them. The
mutualism would end.Figure 20.9
Q1: How do barnacles benefit from living on a whale?A1: The whale provides a home and a constant stream of water
passing over the barnacles to bring them the tiny particles of food
that they filter from the sea.Q2: Do you think a whale could avoid being colonized by
barnacles? Why or why not?A2: It is probably unlikely that a whale could avoid being
covered by barnacles, although since the barnacles do not help
or hurt the whale, there would be no reason for a whale to try to
avoid them.Q3: Explain why detritivores are considered commensal to the
organisms they consume. (You will need to read ahead to answer
this question.)A3: Since the organism is already dead, the detritivore is not
harming it by eating it. The detritivore, though, benefits from the
association.Figure 20.10
Q1: What kind of predator is the cheetah in the figure?A1: Carnivore.Q2: What kind of predator is the louse in the figure?A2: Parasite.Q3: What kind of predator are the elk that graze on aspen tree
saplings?A3: Herbivore.Figure 20.11
Q1: How do predators know that brightly colored prey are usually
toxic?A1: Most predators have experienced through the trial and
error of tasting prey and becoming sick that brightly colored
prey are toxic. Predators must learn by trying one to avoid
others later. If the organism were so toxic that the predator died
from eating one, then bright displays would not help prey avoid
predation.Q2: Do you think mimicry works if the toxic species is in low
abundance? Why or why not?A2: Mimicry is similar to warning coloration in that its benefit is
usually accomplished through trial and error. If there are many
more nontoxic mimics than real toxic individuals, predators that
successfully eat the mimics will not learn to avoid them. Only if it
is more likely that a predator will encounter an actual toxic and