Optimal Group Size

Many animal species form groups for a portion or the entirety of their lives. Individuals benefit from forming groups when the advantages of aggregating – including foraging and hunting benefits, improved predator avoidance, increased conspecific threat avoidance (against infanticide and intergroup contests), cooperative infant care, and information sharing – outweigh the costs of group living – predominantly intragroup resource competition for food and reproductive opportunities, as well as increased exposure to disease.

Group size impacts access to food and the ability to respond to threats and has important fitness consequences (lifetime reproductive success). Optimal group sizeis the group size at which individual member fitness is maximized. Group size is influenced by ecological factors, namely food competition and risk of predation, which put pressure on the upper and lower limits of group membership until an intermediate, optimal size is reached. Intergroup competition is one...