Ecological Specialization and Diversification in Birds

Ecological specialization is widely thought to influence patterns of species richness by affecting rates at which species multiply and perish. Quantifying specialization is challenging, and using only one or a small number of ecological axes could bias estimates of overall specialization. Here, we calculate an index of specialization, based on seven measured traits, and estimate its effect on speciation and extinction rates in a large clade of birds. We find that speciation rate is independent of specialization, suggesting independence of local ecology and the geographic distributions of populations that promote allopatric species formation. Although some analyses suggest that more specialized species have higher extinction rates, leading to negative net diversification, this relationship is not consistently identified across our analyses. Our results suggest that specialization may drive diversification dynamics only on local scales or in specific clades, but is not generally responsible for macroevolutionary disparity in lineage diversification rates.