Competitive Behavior

Each species needs a place to live that provides shelter from bad weather, adequate food and water, and access to mates. Because such resources are limited, competition is often the result. Competition between animals of the same species can be seen in several types of behavior.

Aggressive Behavior

Physical conflict or threatening behavior between animals is called aggressive behavior. This type of behavior includes displays and contests of strength that determine which individual is larger or stronger. The male impalas in Figure 44-7 display aggressive behavior when competing for mates. Most often, these contests result in one animal "surrendering" to the other. Usually, the larger or healthier male wins, and both leave unhurt.

figure 44-7

Male impalas defend their territories against intrusion by other males.

figure 44-7

Male impalas defend their territories against intrusion by other males.

figure 44-8

Male bowerbirds (Amblyornis inornatus) build elaborate nests of various shapes and with different decorations. Females choose a mate based on his bower-building abilities.

figure 44-8

Male bowerbirds (Amblyornis inornatus) build elaborate nests of various shapes and with different decorations. Females choose a mate based on his bower-building abilities.

Territorial Behavior

One way to ensure that an animal is able to obtain sufficient resources for itself, its mate, and its offspring is for the animal to select and establish a territory. A territory is an area that an animal or a group of animals occupies and defends from other members of the same species. An animal establishes a territory in many ways, including marking the boundaries with urine or visual cues, and claiming an area with vocal signals. Territorial animals will threaten or attack intruders.

The male bowerbird shown in Figure 44-8 has established a small territory which includes his nest and the area around it. He has marked the territory by building and decorating a bower and will defend it from other males. Animals may be territorial under certain circumstances. For example, the bowerbird only builds and defends his territory during breeding season. Natural selection can reinforce territorial behavior. When animals space themselves out, they do not compete for the same resources. This behavior increases the likelihood that the young of territorial animals will survive and inherit traits that promote territoriality.

Dominance Hierarchies

Competition can lead to a clear ranking of individuals within the group, from most dominant to most subordinate. This type of ranking, called a dominance hierarchy (HIE-rahr-kee), reduces the need for competition and aggressive behavior as subordinates learn to submit to avoid conflict. One example of a dominance hierarchy is that formed by chickens. The dominant chicken can peck all other chickens. The most subordinate chicken gets pecked by all other chickens in the group. It is from this behavior in chickens that the term "pecking order" is derived.

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