Harem (zoology)

A harem is an animal group consisting of one or two males, a number of females, and their offspring. The dominant male drives off other males and maintains the unity of the group. If present, the second male is subservient to the dominant male. As juvenile males grow, they leave the group and roam as solitary individuals or join bachelor herds. Females in the group may be inter-related. The dominant male mates with the females as they become sexually active and drives off competitors, until he is displaced by another male. In some species, incoming males that achieve dominant status may commit infanticide.

For the male, the main benefits of the harem system is obtaining exclusive access to a group of mature females. The females benefit from being in a stable social group and the associated benefits of grooming, predator avoidance and cooperative defense of territory. The disadvantages for the male are the energetic costs of gaining or defending a harem which may leave him with reduced reproductive success. The females are disadvantaged if their offspring are killed during dominance battles or by incoming males.

The term harem is used in zoology to distinguish social organization consisting of a group of females, their offspring, and one to two males.

The single male, called the dominant male, may be accompanied by another young male, called a "follower" male. Females that more closely associate with the dominant male are called "central females," while females who associate less frequently with the dominant male are called "peripheral females." Juvenile male offspring leave the harem and live either solitarily, or, with other young males in groups known as bachelor herds. Sexually mature female offspring may stay within their natal harem, or may join another harem. The females in a harem may be, but are not exclusively, genetically related. For instance, the females in hamadryas baboon harems are not usually genetically related because their harems are formed by "kidnapping" females from other harems and subsequent herding. In contrast, gelada baboon harems are based on kinship ties to genetically related females. Multiple harems may assemble into larger groups known as "clans" or "teams".

Harem cohesiveness is mediated by the dominant male who fights off invading males to keep claim over the harem. In some harem-forming species, when a dominant male vacates his harem (due to death, defection to another harem, or usurpation) the incoming male sometimes commits infanticide of the offspring. Because time and resources are no longer being devoted to the offspring, infanticide often stimulates the female to return to sexual receptivity and fertility sooner than if the offspring were to survive. Furthermore, while lactating, females do not ovulate and consequently are not fertile. Infanticide therefore has the potential to increase the incoming male's reproductive success.

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