Niche expansion of capuchin monkeys to forest floor on guild-reduced islands increases interspecific spatio-temporal overlap

Interspecific interactions play an important role in structuring wildlife communities. On islands, which often have reduced species assemblages, species may expand their niches resulting in unusual patterns of interactions with other members of the ecological community. In this study, we compared spatio-temporal interactions of two food competitors between a site with predators and two predator-free islands in the Coiba archipelago, Panama. Here, capuchin monkeys (Cebus capucinus imitator) exhibit high levels of terrestriality, and some groups engage in stone tool use. This potentially leads to competition with sympatric agoutis (Dasyprocta coibae), which have overlapping diets. We used camera-trap surveys to estimate temporal overlap between both species, distinguishing between arboreal and terrestrial activity of capuchins. We also compared detection rates and intervals between consecutive detections of both species at sites in which the monkeys use stone tools (tool-use area) and sites in which they do not (non-tool-use area). We found high spatio-temporal overlap between agouti and capuchin on the forest floor of both islands. While capuchins visited the tool-use area four times as often as the non-tool-use area, agoutis avoided the tool-use area, capture rates being 25 times as low. Waiting times were shorter for both species at the tool-use area. These results suggest temporal overlap and spatial segregation. Niche expansions on islands thus cause unique interactions that do not occur on the mainland.