Current models of the evolution of primate behavior suggest that the strength of between-group competition strongly affects fundamental aspects of primate sociality, including female-female and male-female social relationships. Although encounters between groups are found in many species and are often described as aggressive, the functions and consequences of these interactions remain poorly understood. Aggressive behavior during encounters between groups is thought to help defend access to limiting resources or mating opportunities. This study will systematically examine these possible functions of between-group aggression in tufted capuchin monkeys (Cebus apella) at Iguazu National Park, Argentina. The researchers will follow multiple social groups simultaneously and record patterns of individual participation in intergroup encounters, the overall intensity of intergroup aggression, and several factors that may affect these interactions, including the presence of estrous females and vulnerable infants or the proximity to contestable food resources. In addition, the researchers will test if more aggressively successful groups gain or retain access to better quality territories and resources in areas of overlap, using a combination of ecological and behavioral data. The loss or gain of food from encounters and dominance between groups will be compared to similar consequences of aggression among members within a group. To make controlled tests of particular hypotheses, the researchers will simulate the presence of another social group with vocal playback experiments. These experiments will occur near artificially-controlled resources to independently manipulate the social and ecological context of apparent encounters.
Previous studies of intergroup aggression in non-human primates have been unable to collect the detailed behavioral and ecological data necessary to distinguish among all the various hypothesized functions of between-group aggression. This research project will address these gaps by systematically examining the importance of competition for mates and critical food resources. The study will also be used to compare with previously studied Peruvian populations that exhibit reduced intergroup aggression, thereby allowing direct examination of the influence of population differences in resource distribution and availability on between-group competition. The project will provide employment and training for Argentine students, members of the Guarani community, and possibly U.S. undergraduate volunteers.
