A model with many small shifts for estimating species-specific diversification rates.

Understanding how and why diversification rates vary through time and space and across species groups is key to understanding the emergence of today's biodiversity. Phylogenetic approaches aimed at identifying variations in diversification rates during the evolutionary history of clades have focused on exceptional shifts subtending evolutionary radiations. While such shifts have undoubtedly affected the history of life, identifying smaller but more frequent changes is important as well. We developed ClaDS-a new Bayesian approach for estimating branch-specific diversification rates on a phylogeny that relies on a model with changes in diversification rates at each speciation event. We show, using Monte Carlo simulations, that the approach performs well at inferring both small and large changes in diversification. Applying our approach to bird phylogenies covering the entire avian radiation, we find that diversification rates are remarkably heterogeneous within evolutionarily restricted species groups. Some groups such as Accipitridae (hawks and allies) cover almost the full range of speciation rates found across the entire bird radiation. As much as 76% of the variation in branch-specific rates across this radiation is due to intraclade variation, suggesting that a large part of the variation in diversification rates is due to many small, rather than few large, shifts.