Protection from predators . There are three reasons why an individual may live in group to avoid predation. Cooperative defense against predators. Several baboon males can deter a hyena but a solitary baboon will become prey. To buffer themselves from predators sheep form herds, fish swim in schools, and birds fly in flocks.
Predators can t eat an entire group.
An individual lives in a group so as to get someone else between them and a predator. Safety in numbers. This reason is called the selfish herd because, obviously, individuals want to be in the central core of a group, not on the periphery. Cooperative defense against other groups of your species. Some primates form groups and defend valuable resources, such as fruit-trees, against groups of their own species.