Between-group contest competition among tufted capuchin monkeys, Sapajus nigritus, and the role of male resource defence

Between-group contest competition and the relative importance of male resource defence have recently been suggested to have been previously underestimated. When males contribute to the defence of group-controlled resources, the quality of the home range may depend on the resource-holding potential of resident males. Among Argentine tufted capuchin monkeys, resident males defend access to high-quality food resources. Here I investigate consequences of this male–male cooperation for intergroup dominance relationships and home range quality. I recorded ranging behaviour for four habituated groups in Iguazú National Park to identify home ranges and core areas, and measured the availability of food species within botanical plots placed in these areas. I recorded the location and outcome of intergroup encounters and fitted predictive models using generalized estimating equations to assess the relative importance of male group size and location on the outcome, before performing linear mixed-effects modelling to identify long-term benefits of winning encounters. Relative male group size was the most important factor in determining the winner of encounters, outweighing the competitive advantage of ownership. The density of food species within the core area was not affected by the groupʹs competitive ability, but core area size increased with male group size. Moreover, dominant groups were better able to defend their core area, and adjusting for the degree of home range overlap revealed that dominant groups may have higher per capita access to food. These results suggest that male–male cooperation in defence of food resources could ultimately increase female reproductive success.