Dissertation Research: Ecological Bases of Agonistic Coalitions in Capuchin Monkeys

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The ecological basis for pair-wise aggressive encounters has been investigated in many species of non-human primates. Some species also form aggressive coalitions while searching for food, but the ecological correlates of such coalitions have yet to be studied. A coalition is defined as cooperation by two or more individuals in an aggressive encounter against one or more other individuals. This study will focus on pair-wise and coalitional aggression in the white-faced capuchin, Cebus capucinus in the context of feeding. The objectives of this study are (1) to measure the ecological factors that may affect the rates of aggressive contests by quantifying the costs and benefits associated with resource competition and (2) to test an ecological explanation for the evolution of coalition behavior in non-human primates. Data will be collected at two dry-forest study sites in Costa Rica. The researchers will examine whether the ecological costs and benefits associated with coalition formation differ systematically from those that prevail during pair-wise contests, and whether males and females are equally likely to form coalitions. Because males are usually dominant to females in C. capucinus, one would expect females to form coalitions to gain access to food patches occupied by a male. The ecological benefit of fighting over a food patch will be measured as the nutritional gain available to contestants in the patch, whereas the cost to an individual includes both the cost of a physical injury and the time needed to find alternate food patches if it loses. The ecological explanation will be tested against the simple alternative that the frequency of fights and coalitions reflect overcrowding or the availability of coalition partners in a food patch. This study will help us to understand the origins of cooperative behavior in non-human primates and humans.