Biology Now, 2e

Answers ■ A37

bad-tasting prey will it learn to avoid anything that looks similar

to the prey it encountered.

Q3: Why is camouflage considered an adaptive response to

predation?

A3: Camouflage enables prey species to blend in with their

surroundings so that they’re difficult for predators to detect.

Random variation in coloration of a population enables those that

are better hidden from predators to survive and reproduce, while

those that do not match the surroundings well are easily seen and

eaten. Over time, only well-camouflaged prey survive to reproduce,

passing the camouflage coloration on to their offspring.

Figure 20.12

Q1: What percentage of pigeons are caught when they are alone

and not in a flock?

A1: Very close to 80%.

Q2: For wood pigeons, what is the minimum number of

individuals that provides protection from goshawks?

A2: 11 individuals.

Q3: Why do you think a group of musk oxen versus a lone musk ox

would be safer from a pack of wolves?

A3: The group of musk oxen could form a circle in which they

faced out and use their large horns to impale the wolves, keeping

their sides and rear ends protected from attack. A lone ox would

be completely unprotected from a pack of wolves working

together.

Figure 20.13

Q1: Which species appears to be the superior competitor?

A1: Aphytis lingnanensis.

Q2: Why is this example considered exploitative competition?

A2: These wasp species feed on the same foods in the same place

but never physically come in contact with each other. They are in

direct competition but do not physically interact.

Q3: What would you predict if these species had undergone

competitive exclusion? (You will need to read the next paragraph

to answer this question.)

A3: The first species would now be exploiting another resource—

for example, apples rather than citrus.

Figure 20.15

Q1: What species represents the first colonizers of the sand

dunes?

A1: Dune-building grasses.

Q2: What species is the intermediate species, and how does it

become the dominant species?

A2: The pine is the intermediate species. It likely becomes

dominant by outcompeting the grasses for water, nutrients, and

sunlight. Once established, the pines’ shade further inhibits the

growth of grasses.

Q3: What species is the mature, climax community species, and

how does it become the dominant species?

A3: The black oak is the mature, climax community species. It

likely becomes the dominant species because it outcompetes the

pines for water, nutrients, and sunlight.

Figure 20.16

Q1: What other types of disturbances could you imagine

destroying a forest?

A1: Other types of disturbances could include clear-cutting or

heavy logging, abandonment of agricultural fields, flooding,

clearing by tornado or hurricanes, and the creation of empty lots

in a newly built subdivision, among others.

Q2: How is secondary succession different from primary

succession?

A2: Secondary succession starts with some existing producers

that survived a disturbance, whereas primary succession starts

from nothing—pure rock or sand. A disturbance that would result

in primary succession would be a lava flow that covered an entire

area; succession would have to start from pure lava rock and no

existing producers.

Q3: What is a climax community?

A3: A climax community is the final step in succession, in which

the species in the community remain and are not replaced by any

other species as time goes by.

CHAPTER 21

END-OF-CHAPTER ANSWERS

1. a


2. c


3. d


4. c


5. biome: 3, ecosystem: 2, net primary productivity: 1, ecological
   community: 4


6. chaparral, grassland, estuaries


7. b


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


9. An ecosystem is composed of multiple ecological commu-
   nities, and it also includes physical environmental factors
   (communities do not).


10. (a) 100. (b) 100,000. (c) The energy is expended in metab-
    olism, and since predation is not 100% efficient (that is,
    predators don’t eat every last bit of the calories in their prey,
    leaving, for example, the bones), some energy is lost there too.


11. The water cycle is more similar to the movement of nutrients,
    because water cycles through the biotic and abiotic compo-
    nents of an ecosystem, whereas energy flows in only one direc-
    tion through ecosystems because of the steady loss of heat.


12. c