Chapter 7 - Group Size and Composition

Abstract

The tendency to form groups provides opportunities to increase foraging efficiency and decrease predation risk, but entails costs such as increased competition. Striking a balance between the costs and benefits of foraging in groups should lead to the formation of groups that maximize individual fitness. However, the expected group size will vary depending on whether entry in the group is free or constrained. In a free-entry system, groups are expected to be larger than the optimal size, while groups that control entry may be closer to the optimal value. The paradox that groups often tend to be larger than the optimal size in a free-entry system can be resolved through many means. In particular, relatedness, within-group competition, and learning about habitat quality may all act to keep the size of a group closer to the optimal value. Group composition has emerged as an important consideration when assessing the fitness consequences of group living. Segregation of groups along phenotypic traits, such as size, has been documented in many species, and certainly suggests that individuals pay attention not only to the size but also to the composition of their groups.