10 Predation
We start by describing the behavior of predators with respect to prey. With this know-
ledge we explore some theoretical models for predator–prey interactions. Finally, we
examine how the behavior of prey can influence the rate of predation. This chapter
complements the approach given in Chapter 12 for analyzing interactions between
trophic levels.
The previous two chapters have dealt with interactions between individuals on the
same trophic level. Predation usually involves interactions between trophic levels where
one species negatively affects another. With respect to our three issues of manage-
ment – conservation, control, and harvesting – predators and predation are of great
interest. For rare prey species, the presence of a predator can make the difference
between survival or extinction of the prey, especially if the predator is an introduced
(exotic) species. This type of problem is particularly important on small islands, but
also on isolated larger land areas such as New Zealand and Australia. In contrast,
where prey are pests, predators may be useful as biological control agents. Ironically,
it was for just this purpose that the small Indian mongoose (Herpestes auropunctatus)
was introduced to Hawaii and the stoat (Mustela erminea) to New Zealand. Unfor-
tunately, in these cases the predators found the indigenous birds and small marsu-
pial mammals easier to catch, so that the predators themselves became the problem.
Finally, where harvesting of a prey species (by sport hunters, for example) is the
objective, the offtake by natural predators must be taken into account, or one runs
the risk of overharvesting and causing a collapse of the prey population.
Predation can be defined as occurring when individuals eat all or part of other live
individuals. This excludes detritivores and scavengers which eat dead material.
There are four types of predation.
1 Herbivory. This occurs when animals prey on green plants (grazing, defoliation) or
their seeds and fruits. It is not necessary that the plants are killed; in most cases they
are not. Seed predators (granivores) and fruit eaters (frugivores) often kill the seed,
but some seeds require digestion to germinate. We discuss herbivory in Chapter 12.
2 Parasitism. This is similar to herbivory in that one species, the parasite, feeds on
another, the host, and often does not kill the host. It differs from herbivory in that
the parasite is usually much smaller than the host and is usually confined to a
single individual host. The behavior of nomadic herders in Africa who live entirely
on the blood and milk of their cattle would also fit the definition of parasitism. Insect
parasites (parasitoids) lay their eggs on or near their host insects which are later killed
and eaten by the next generation. We discuss parasitism further in Chapter 11.
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10.1 Introduction
10.2 Predation and management
10.3 Definitions
