Effects of phylogeny and geography on ecomorphological traits in passerine bird clades

Aim: Closely related species are often morphologically similar due to their shared evolutionary history. This similarity can restrict their geographic distribution, as processes such as interspecific competition might prevent species from co-occurring if they resemble each other too closely. There is still little understanding of the relative strengths of such phylogenetic and geographic effects on the morphological diversity of species within a clade. Here, we compare phylogenetic effects with geographic effects across multiple clades of passerine birds to understand the roles of evolutionary history and geographic patterns on the ecomorphological characteristics of species. Location: Global Methods: We combine phylogenetic and geographic approaches to investigate and compare their effects on patterns of ecomorphological distinctness, i.e. the relative position of species in multidimensional ecomorphological trait space. The trait space was based on measurements from preserved specimens, representing ecologically relevant morphological adaptations across almost 500 species in eight clades of the order Passeriformes. Results: Ecomorphological distinctness increased with phylogenetic distance across species in all clades, whereas there was no significant relationship between geographic and ecomorphological distinctness in any clade. However, we observed a significant interaction between phylogenetic and geographic effects on ecomorphological distinctness. Closely related species were ecomorphologically indistinct if in geographic proximity, while at large geographic distances, there was no relationship between phylogenetic and ecomorphological distinctness. Main conclusions: We conclude that phylogenetic relationships are influential in shaping ecomorphological traits in passerine bird clades, but that this effect depends on the geographic distributions of species. Closely related species were only ecomorphologically similar when geographically close, suggesting a signal of allopatric speciation. Our results imply that studies identifying phylogenetic effects in species’ traits should not focus exclusively on these but instead evaluate the interaction of phylogenetic effects with geographic effects.