In primatology, a fission-fusion society is one in which the social group, e.g. bonobo collectives of 100-strong, sleep in one locality together, but forage in small groups going off in different directions during the day. This form of social organization occurs in several other species of primates, though usually less organised and less social than bonobos (e.g. chimpanzees, hamadryas, gelada baboons, spider monkeys, and humans), most carnivores including the spotted hyena, African lion, and cetaceans such as bottlenose dolphins, ungulates such as deer, and fish such as guppies. 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 in favor of associating themselves with another, usually for reproductively motivated reasons.