Food and range defence in group-living primates

Why do some primate groups contest access to food resources primarily at territorial borders (periphery defence), whereas others are more likely to contest resources in the centre of the home range (core defence)? One possibility is that central areas contain more food resources and so are more important for core-defending groups, whereas peripheral areas are more valuable for groups that defend territorial boundaries. I tested this hypothesis by analysing the distribution of resources in home ranges and aggressive intergroup interactions for six groups of grey-cheeked mangabeys, Lophocebus albigena, and six groups of redtail monkeys, Cercopithecus ascanius, at the Ngogo site in Kibale National Park, Uganda. Neither mangabeys nor redtails exhibited core or boundary defence in this study; instead, both species appeared to defend discrete feeding sites, and neither the core nor peripheral home range areas consistently contained greater quantities of food. I also compared variables that are frequently used to characterize primate food availability (the feeding value of the interaction site versus food abundance, distribution and patch size) to determine if they are equally accurate in predicting aggressive food defence. Whereas site feeding intensity predicted aggression by redtails, aggression by mangabey males correlated with the abundance and distribution of resources. These results demonstrate the importance of testing multiple aspects of food availability, which can vary in importance among different primate populations. I conclude by proposing a new model of food and range defence in group-living primates that predicts specific relationships between various food characteristics and core, patch and periphery defence.