Predation, Herbivory, and Keystone Species

How do predation and herbivory shape communities?

Virtually all animals, because they are not primary producers, must eat other organisms to obtain energy and nutrients. Yet if a group of animals devours all available food in the area, they will no longer have anything to eat! That's why predator-prey and herbivore-plant interactions are very important in shaping communities.

Predator-Prey Relationships An interaction in which one animal (the predator) captures and feeds on another animal (the prey) is called predation (pree DAY shun). Predators can affect the size of prey populations in a community and determine the places prey can live and feed. Birds of prey, for example, can play an important role in regulating the population sizes of mice, voles, and other small mammals.

Herbivore-Plant Relationships Interactions between herbivores and plants, like the one shown in Figure 4 –8, are as important as interactions between predators and prey. An interaction in which one animal (the herbivore) feeds on producers (such as plants) is called herbivory. Herbivores can affect both the size and distribution of plant populations in a community and determine the places that certain plants can survive and grow. Herbivores ranging from caterpillars to elk can have major effects on plant survival. For example, very dense populations of white-tailed deer are eliminating their favorite food plants from many places across the United States.

FIGURE 4–8 Herbivory The ring-tailed lemur is an herbivore—meaning that it obtains its energy and nutrients from plants like the cactus it's eating here.

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