Intragroup aggression, fission-fusion dynamics and feeding competition in spider monkeys

Scramble competition is related to animals depleting resources before others can use them, whereas contest competition is associated with the monopolization of resources and food-related aggression. One hypothesized major benefit of fission-fusion sociality is the reduction of scramble feeding competition between community members. We studied intragroup aggression in a community of spider monkeys. Despite seasonal variation in food availability, we found no seasonal difference in aggression rates, which, in combination with a basic lack of aggression among adult females, suggests that fission-fusion dynamics may reduce not only scramble, but also the intensity of contest competition. There were, however, numerous attacks from adult females towards subadult females, especially new immigrants. This aggression, although it occurred mainly during feeding, may not reflect contest competition. Instead, it may be used by resident females to limit scramble competition at the community level, which is ultimately affected by the number of community members. The aggressive harassment of subadult females by long-term resident females can be a means to encourage dispersal of natal subadult females and discourage immigration of new subadult females who are both potential future resource competitors.