How does sociality influence the dominance hierarchies of ecological competitors? Here, we address this question using a large dataset of competitive interactions among birds foraging at backyard feeders across North America, representing a network of over 88,000 interactions among 196 bird species. We quantify sociality as the number of conspecifics observed together, and measure the effects of sociality on competitive displacement interactions at both the among- and within-species levels.
Results/Conclusions
We show that sociality varies across bird species, as indicated by significant repeatability in group size. More social species are less likely to dominate a similarly sized competitor, yet more social species also gain a greater competitive advantage from the presence of their conspecifics. This suggests that social clustering is associated with the evolution of reduced interspecific competitive ability. We found that within-species competition occurs more often than expected in a null model, with the most social species exhibiting the greatest proportion of conflict originating from conspecifics. Overall, these results demonstrate how sociality influences the outcome of competition in ecological networks. Species that evolve greater sociality exhibit decreased competitive ability as individuals, but increased competitive ability in groups.
