Cooperation and colony size as drivers of differential resource use among sympatric social predators

Dietary differentiation is an integral component of species coexistence, and among solitary predators, body size differences allow each species to capture a different range of prey sizes. Social predators, however, are able to capture much larger prey than an individual, so prey size use is additionally influenced by group size and behavioural dynamics. To investigate this, we looked at cooperative hunting among three species of sympatric group-living spiders in Brazil that construct colonies of different sizes and are known to capture different sizes of prey. We performed feeding experiments to determine whether differential prey size use is produced by differences in group behaviour and group size. For each species we measured the level of cooperation and examined how colony size influenced group behaviour. We found that two of the species which live in equally large, multi-generational colonies displayed differences in their cooperation and prey size selectivity that are consistent with differences in prey size use previously observed: the species which captures larger prey in natural hunting scenarios showed higher levels of cooperation among hunters during the trials, and had more individuals participate when presented with large prey. The third species, which lives in smaller, temporary colonies, displayed the highest levels of cooperation and prey capture success, despite capturing the smallest prey on average in natural hunting scenarios. This disparity likely reflects the natural size distribution of colonies of this species, which is greatly dominated by solitary individuals that cannot capture the largest prey on their own. This study shows that behavioural differences among group-living predators, in addition to colony size differences, may be responsible for differential prey size use.Science, Faculty ofZoology, Department ofGraduat