Social Behavior

A society consists of conspecific individuals organized in a cooperative manner and extends beyond sexual and parental behavior. Typically, males do little care taking of the young, commonly being polygynous and involved with other mating relationships. The females, however, are necessarily care takers and most mammalian social systems are matrilineal in nature. That is, mothers and offspring stay together and eventually the group consists largely of close female relatives: mothers, daughters, sister, nieces, etc. Males usually disperse as they become mature and tend to be unrelated to members of any group they might join.

Nearly all mammalian orders have some species with complex social organization, but such are most common among carnivores, whales, and primates. The species that are most apt to have complex social setup in any higher taxon usually are those that have large brains and are large in body size. Among terrestrial, highly social groups, there is a tendency to forage above ground in open habitats during the day.

Some examples of social cooperation follow:

Alarm calls. Various mammals, such as social ground squirrels, often give an alarm when a predator is sighted. This allows escape of other members of the social group, but may result in a higher mortality for the individuals who give the alarm. Activities that decrease the changes of reproduction of the individual but that may aid others in the group are said to be altruistic.

Cooperative rearing of young. Many mammals (and some other vertebrates) have systems where one parent or one pair of parents produce the young, but other members of the group join in raising the young. In other species, there may be a number of females producing young, but the females do not discriminate in care taking. In African lions, for example, females will nurse young born to other females. In wolves, only the alpha female produces young, but subordinate members of the group will regurgitate food for the alpha female and her litter. Numerous other examples are possible.

Coalitions and alliances. We've mentioned some of the dominance patterns earlier that fit into this heading. In some others, such as rhesus monkeys, the higher-ranking males act as "control" animals. These will protect the group if the group is seriously challenged by a different group. They also will intervene in intragroup fights. In reciprocal behavior, such as seen among chimpanzees, an individual who has intervened on behalf of another individual often will have the other individual intervene on the behalf of the first. This, of course, requires keeping track of who has done what to (and for) whom; not surprisingly, such complex behaviors in primates tend to correlate with brain size.

Eusociality. Eusociality is characterized by cooperation in the care of young; reproductive castes with non-reproductive individuals caring for reproductive nestmates; and overlap between generations, with the offspring of one generation assisting in the care of their later siblings. The mole-rat is the mammalian example of this. One female breeds, with the female and her brood fed (but not nursed) by worker-caste individuals (both males and females), but were never seen to breed; a different castes of non-workers helped keep the young warm and the males of this castes did breed with the queen.

There are both benefits and costs associated with sociality. Benefits include protection against predators, both by alarm spreading and by mobbing. There also may be benefits in obtaining food. Group efforts of wolves and lions make possible taking of large prey that would be impossible to obtain otherwise. In bighorn sheep, the locations of feeding grounds and migratory routes are passed on to younger members of the herd. Defense of feeding territories against others of the same species also is a benefit; this is done by African lions and wolves, for example. Leks are formed by some mammals, where a number of males collect on the lek and display for the females to entice copulation. Hammer-head bats and fallow deer are example of such mammals. The opportunity to learn is important in some groups, but requires a long period of dependency (up to 25% of the life span in some dolphins and primates).

Costs have been less studied. There may be more intraspecific competition. In prairie dog colonies, the amount of aggression between members of the colony increases as colony size increases. Again, based on prairie dog colonies, the larger and denser the colony, the greater the ectoparasite infestation is; since colonies periodically are devastated by bubonic plague, members of larger colonies are at greater risk. There also may be interference with reproduction, with young killed by others. Lions are notorious for this, small cubs almost always being killed when new males take over a pride.

Last Update: 5 Feb 2008