Species distributions and coexistence patterns are shaped by environmental conditions and interactions with other species through suites of evolutionary-defined ecological characteristics, or traits. Community ecology has historically focused on explaining these patterns at the scale of local species assemblages, recognizing their hierarchical scaling into regional species pools controlled by macroevolutionary and macroecological processes. The last decade has seen a rising interest in these larger-scale perspectives on species coexistence, with the development and testing of theories that explain how regional pools and local communities interplay to shape diversity gradients. However, how species’ ecological traits contribute to structure coexistence at large scales has been understudied. In this study, we quantified the extent to which traits explain the history of global patterns of bird species coexistence, expressed through the phylogenetic structure of regional assemblages. We quantified phylogenetic fields, describing the evolutionary relatedness of each of >8000 bird species with the assemblages in which they occur throughout their geographic ranges, and related them to biometric, dietary and dispersal traits by means of ordinary and phylogenetically constrained regressions.
Results/Conclusions
50% of terrestrial bird species are more phylogenetically distant from the assemblages in which they occur than would be predicted by a null model of species co-occurrence, while 40% were phylogenetically closer than predicted. Thermal preference, dietary traits and migration were prominent in explaining these patterns, while body size and dispersal strategies had weaker effects and habitat preference was unimportant. These patterns were driven by a strong phylogenetic signal, suggesting that these ecological traits have evolved little after early separation of ancestral species. This matches the prediction from the tropical niche conservatism hypothesis that only few clades have been able to diversify outside the tropics. The trait relations further suggest that these climatic constraints probably have arisen through key constraints related to diet and mobility. Based on these results, we propose that building a framework which enables the integration of spatial and species-oriented approaches to coexistence patterns will provide critical insights to the large-scale processes that shape regional species assemblages.