Biology Now, 2e

Answers ■ A35

Figure 19.10

Q1: In what year did the bald eagle population rise to more than

2,000 breeding pairs?

A1: About 1986 or 1987.

Q2: Give some examples of possible density-dependent limits on

bald eagle populations.

A2: Examples include numbers of prey available, adequate habitat

for nesting and hunting, and availability of water.

Q3: Is the population growth of bald eagles more like logistic or

exponential growth? Explain why you think so.

A3: The population growth of bald eagles is more like logistic

growth in that it is more of an S-shaped curve—at least between

1960 and 2005, where it seemed to level off for a few years. On

the other hand, between 2005 and 2010 the growth appears to be

exponential.

Figure 19.11

Q1: During which years did the hare likely have the greatest food

supply?

A1: 1865 and 1888.

Q2: Besides the number of hare, what other factors might

contribute to the number of lynx?

A2: Other possible factors include the quality of habitat for

building dens and raising young, the availability of freshwater, and

the competition with other lynx and other predators of the hare.

Q3: Can you draw an average carrying-capacity line on these

graphs? Why or why not?

A3: It would be difficult to draw a line representing a carrying

capacity for both of these animals because of the way they go

through cycles of “boom and bust” in population size. They do not

show logistic growth, where the leveling off of the S-shaped curve

provides an obvious carrying capacity.

CHAPTER 20

END-OF-CHAPTER ANSWERS

1. d


2. b


3. c


4. c


5. secondary consumer, primary consumer, producer


6. e


7. mutualism: 2, commensalism: 3, predation: 1, competition: 4


8. (a) 4, (b) 1, (c) 2, (d) 3, (e) 5


9. More diverse communities have low relative species abun-

dance and high species diversity.

10. c
    11. Relative species abundance will decrease, and species richness
    will increase.
    12. (a) S, (b) S, (c) P, (d) P
    13. (a) humans and killer whales, (b) phytoplankton, (c) baleen
    whale and sperm whale, (d) other herbivorous plankton

ANSWERS TO FIGURE QUESTIONS

Figure 20.2

Q1: List another species that is part of this community.

A1: One possible answer: the wolf.

Q2: Of which community could this aspen woodland be a smaller

part?

A2: A larger deciduous forest community.

Q3: Which other small communities could be found within this

larger community?

A3: Many other communities could exist, including soil

communities (soil-dwelling insects, other invertebrates, and

microbes), communities of plants and animals residing in the

undergrowth of the forest, and canopy communities of animals

that live in the treetops, among others.

Figure 20.3

Q1: If relative species abundance increased in the first community,

how would the figure look different from now?

A1: There would be even more trees of the white-trunked species,

and fewer of the other species.

Q2: If species richness decreased in the second community, how

would the figure look different from now?

A2: There would be fewer different species of trees.

Q3: How do relative species abundance and species richness define

the species diversity of a forest community?

A3: High species diversity relies on having each species in

reasonable abundance, and not on one species taking up the

majority of space in an area (relative abundance), and on there

being many different species in a given area (richness).

Figure 20.4

Q1: How many species were left in 1966 in the community where

sea stars were not removed?

A1: About 17 or 18.

Q2: How many species were left in 1966 in the community where

sea stars were removed?

A2: Only 2 or 3.

Q3: How do your answers to questions 1 and 2 demonstrate the

importance of a keystone species for the maintenance of diversity

in a community?

A3: The species diversity plummeted as a result of the loss of

this sea star. Without this species, the entire mussel community

changed from many species to only a few.