Data from: Is specialization an evolutionary dead-end? Testing for differences in speciation, extinction and trait transition rates across diverse phylogenies of specialists and generalists.

Specialization has often been claimed to be an evolutionary dead-end, with specialist lineages having a reduced capacity to persist or diversify. In a phylogenetic comparative framework, an evolutionary dead-end may be detectable from the phylogenetic distribution of specialists, if specialists rarely give rise to large, diverse clades. Previous phylogenetic studies of the influence of specialization on macroevolutionary processes have demonstrated a range of patterns, including examples where specialists have both higher and lower diversification rates than generalists, as well as examples where the rates of evolutionary transitions from generalists to specialists are higher, lower or equal to transitions from specialists to generalists. Here we wish to ask whether these varied answers are due to differences in macroevolutionary processes in different clades, or partly due to differences in methodology. We analyse ten phylogenies containing multiple independent origins of specialization, and quantify the phylogenetic distribution of specialists by applying a common set of metrics to all datasets. We compare the tip branch lengths of specialists to generalists, the size of specialist clades arising from each evolutionary origin of a specialized trait, and whether specialists tend to be clustered or scattered on phylogenies. For each of these measures, we compare the observed values to expectations under null models of trait evolution and expected outcomes under alternative macroevolutionary scenarios. We find that specialization is sometimes an evolutionary dead-end: in two of the ten case studies (pollinator-specific plants and host-specific flies), specialization is associated with a reduced rate of diversification or trait persistence. However, in the majority of studies, we could not distinguish the observed phylogenetic distribution of specialists from null models in which specialization has no effect on diversification or trait persistence.