Increase parasite and disease load. There is an incidental reason why some animals live in groups. Concentrated valuable resources attract individuals. E.g., birds don t nest on cliffs because they benefit by being in a group. Cooperative food collection .
Wolves hunt together.
By doing so each can more easily track and take down large game. Although the individual has to share meat, each still benefits from group hunting. Group hunting is less important in primates. Chimps hunt some but meat is not a major part of their diets. Group hunting is important in many human societies, however.