Social Behavior

How do social behaviors increase an animal's evolutionary fitness?

Whenever birds sing, bighorn sheep butt heads, or chimpanzees groom each other, they are engaging in social behavior. Social behaviors include courtship, territoriality, aggression, and the forming of societies. Choosing mates, defending or claiming territories or resources, and forming social groups can increase evolutionary fitness.

FIGURE 29–8 Types of Social Behavior Social behaviors such as courtship and territorial marking help define social groups.

Courtship For sexually reproducing animal species, evolutionary survival requires individuals to locate and mate with another member of its species at least once. Courtship is behavior during which members of one sex (usually males) advertise their willingness to mate, and members of the opposite sex (usually females) choose which mate they will accept. Typically, males send out signals—sounds, visual displays, or chemicals—that attract females. The musical trill of a tree frog, for example, is a breeding call.

In some species, courtship involves an elaborate series of behaviors called rituals. A ritual is a series of behaviors performed the same way by all members of a population for the purpose of communicating. Most rituals consist of specific signals and responses that continue until mating occurs. For example, gannets bond by engaging in “beak-pointing”—intertwining their necks while pointing their beaks to the sky, a behavior you can see in Figure 29–8.

Territoriality and Aggression Many animals behave in ways that prevent other individuals from using limited resources. Often, these animals occupy a specific area, or territory, that they defend against competitors. Territories usually contain resources, such as food, water, nesting sites, shelter, and potential mates, which are necessary for survival and reproduction. If a rival enters a territory, the “owner” of the territory attacks in an effort to drive the rival away. Grizzly bears will often mark their territories with their fur and scent by scratching their backs on rough surfaces, such as trees or signposts.

While competing for resources, animals may also show aggression, threatening behaviors that one animal uses to exert dominance over another. Fights between male sea lions over territory and “harems” of females often leave both rivals bloodied.

Animal Societies An animal society is a group of animals of the same species that interact closely and often cooperate. Mammals form many types of societies, which offer a range of advantages. Zebras and other grazers, for example, are safer from predators when they are part of a group than when they are alone. Societies can also improve animals' ability to hunt, to protect their territory, to guard their young, or to fight with rivals. In wild African dog packs, for instance, adult females take turns guarding all the pups in the pack, while the other adults hunt for prey. Macaque, baboon, and other primate societies hunt together, travel in search of new territory, and interact with neighboring societies.

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