This is a project to test a new model of how competition for food and risk of predation interact to affect primate group size and structure. Most models that predict primate group size treat predation risk and within-group food competition as distinct factors which can be measured independently from each other. In contrast, Janson proposes a mathematical model in which, for a given habitat, both an individual monkey's food intake and predation risk are functions of four socioecological parameters: group size, spacing between individuals, time spent vigilant, and time spent foraging. Because parameter values which decrease risk of predation also decrease food intake, the optimal social group size in this model is remarkably independent of the intensity of predation, while the other socioecological parameters covary with group size in well-defined ways. Data on brown capuchin monkey social structure will be collected on four groups in a low-predation environment in a National Park in Argentina, and compared with data previously collected by the PI on the same species in a high-predation environment in Peru. The proposed study will be the first in which differences in both food availability and predation risk between populations are measured and related to specific differences in social structure.
