Rates of diversification vary greatly among taxa. Understanding how species-specific traits influence speciation rates will help elucidate mechanisms driving the production and maintenance of biodiversity over broad spatiotemporal scales. Ecological specialization and range size are two characteristics thought to predict differences in speciation rates among clades, yet each mechanism predicts both increases and decreases in speciation. We estimate a continuous index of specialization using avian bill morphology. We determine the relative effect of specialization and range size and shape on speciation rates across 559 species within the Emberizoidea superfamily, a morphologically diverse clade distributed across the Americas and associated islands. We find a significant positive correlation between specialization and speciation rate, and a negative correlation with range size. Only the effect of specialization persisted after removing island endemics, suggesting that ecological specialization is an important driver of diversity across large macroevolutionary scales and the relative importance of specific drivers may differ on islands and continents.

MorphRangeData .csv file containing specialization and range data for species included in the analyses Geomorph_PCScores .csv file containing the PC scores used in the QuaSSE and MuSSE analyses SSEModels.R Code to replicate MuHiSSE, QuaSSE, and MuSSE analyses ESSim.R Code to replicate ES-sim and FiSSE analyses ALL_TPS_FILES Raw coordinate data produced from TPSDig, used in Geomorph package to generate specialization index and PC scores TPS_FILES_ImageID_Species File used to match ImageID from shape coordinate data to species names Geomorph.R Code used to analyze shape data and generate specialization index and PC Scores