In ethology, a fission–fusion society is one in which the size and composition of the social group change as time passes and animals move throughout the environment; animals merge into a group (fusion)—e.g. sleeping in one place—or split (fission)—e.g. foraging in small groups during the day. For species that live in fission–fusion societies, group composition is a dynamic property.
This form of social organization occurs in several species of primates (e.g. chimpanzees and bonobos, hamadryas baboons, geladas, orangutans, spider monkeys, and humans), African elephants, most carnivores including the spotted hyena, African lion, and cetaceans such as bottlenose dolphins, ungulates such as deer, plains zebras, giraffes, and fish such as guppies.
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These societies change frequently in their size and composition, making up a permanent social group called the "parent group". Permanent social networks consist of all individual members of a faunal community and often varies to track changes in their environment and based on individual animal dynamics.
In a fission–fusion society, the main parent group can fracture (fission) into smaller stable subgroups or individuals to adapt to environmental or social circumstances. For example, a number of males may break off from the main group in order to hunt or forage for food during the day, but at night they may return to join (fusion) the primary group to share food and partake in other activities.
Overlapping of so-called "parent groups" territorially is also frequent, resulting in more interaction and mingling of community members, further altering the make-up of the parent group. This results in instances where, say, a female chimpanzee may generally belong to one parent group, but encounters a male who belongs to a neighboring community. If they copulate, the female may stay with the male for several days and come into contact with his parent group, temporarily "fusing" into the male's community. In some cases, animals may leave one parent group to associate themselves with another, usually for reproductive reasons.
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