Ecomorphology is associated with speciation and co-occurrence in Sceloporus lizards

Closely related species can impose strong forces of selection on one another through competition, leading to dramatic examples of phenotypic evolution. Niche partitioning can promote the use of novel resources between co-occurring species to reduce competitive overlap and thereby drive phenotypic divergence. Quantifying this potential relationship between ecology and morphology among species can reveal how opportunity and constraint interact to shape patterns of phenotypic evolution and how phenotypic diversity can facilitate co-occurrence. We explored the dynamics of ecomorphological evolution in relation to speciation and co-occurrence in Sceloporus lizards, a speciose group spanning North and Central America, where species often occur in sympatry. We collected data for 80 species and demonstrated strong relationships between multivariate morphology and ecology, finding that Sceloporus species occur in six ecological modes with associated morphologies (ecomorphs). The evolution of arboreality was a major transition that expanded morphospace, allowed for the evolution of further ecological novelty, and is associated with increased speciation rates. Across their range, Sceloporus ecomorphs are spatially overdispersed, suggesting that interspecific competition may limit the ability of similar species to coexist. By quantifying ecomorphological diversity across a diverse radiation, our results shed new light on how phenotypic variation accumulates and its implications for coexistence between closely related species.