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5 The ecology of behavior

In this chapter we consider how ecological constraints shape the behavior of indi-

vidual organisms and, conversely, the effect of individual behavior on the dynamics of

populations and communities. This is part of the field known as behavioral ecology.

We concentrate on foraging and social interactions because these characteristics often

have important ecological ramifications that affect wildlife conservation and man-

agement. We start with a consideration of the many ways that organisms can choose

what and where to eat, then move on to consider how ecological constraints affect

social organization.

The range of mechanisms by which animals choose their diet is diverse. Some

animals have a narrow range of preferences, sometimes even for a single species of

plant. One of the best examples of this is the giant panda, which has evolved a

special set of adaptations allowing it to feed largely on bamboo plants growing on

the steep mountainsides of southern China (Schaller et al. 1985). Such species

are termed feeding specialists. Other species tend to the opposite extreme – feeding

relatively indiscriminately from a wide range of items. A good example of this would

be the moose, which feeds from a wide array of plants, including grasses, woody plants,

herbs, forbs, and even aquatic plants (Belovsky 1978). Such species are termed feed-

ing generalists. Most wildlife species would fall between these extremes.

One can see an immediate advantage in having a broad diet: there is a much

better chance of finding something to eat, no matter where the individual might

find itself. There is also a disadvantage, however, to being a generalist: many of the

possible items in the environment may be so nutritionally poor that they are scarcely

worth pursuing, as we discuss in Chapter 4. For a herbivore, it may be impossible

for an individual to survive on poor-quality items, even when supplies are unlim-

ited. For carnivores, variation among prey derives less from differences in nutritional

quality than from differences in size, visibility, ease of capture, or the associated risk

of injury during capture. In both cases, choosing wisely (becoming a specialist) among

a wide range of food items might prove advantageous. Much foraging theory relates

to this question: how does an animal choose a diet that yields the highest rate of

energy gain over time, energy that can be devoted to enhancing survival and repro-

duction? This question forms the core of optimal foraging theory, a set of mathe-

matical models predicting the patterns of animal behavior that might be favored by

natural selection (Stephens and Krebs 1986).

The simplest way to consider optimal diet is to start with the functional response:

the rate of consumption in relation to food availability (we discuss this further

in Chapters 10 and 12). Most organisms have a decelerating functional response to

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5.1 Introduction

5.2 Diet selection

5.2.1Optimal diet

selection: the

contingency model

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