Ecological and evolutionary determinants of species richness and phylogenetic diversity for island snakes.

Aim Island biogeography predicts positive relationships between area and species richness resulting from the ecological processes of colonization in smaller areas and the evolutionary process of in situ diversification in larger areas. However, the relative contribution of these ecological and evolutionary processes to diversity on islands over time is unclear without associated measures of phylogenetic diversity ( PD), which account for the evolutionary distinctiveness of component taxa. Location Global. Methods We assemble a global dataset of island richness for snakes, along with a phylogeny for the group, to examine the origins of species richness and PD on islands. Results Ecological models driven by colonization explain a majority of species richness in island snake faunas, while in situ diversification is rare, restricted to a few large islands and rarely contributing significantly to island richness. Similarly, PD on islands is tied to variables that affect colonization probability such as isolation and climate, but not area, indicating that in situ diversification does not exert a significant influence on island richness. Main conclusions Even large islands with high in situ diversification do not produce phylogenetically distinct faunas, but are instead dependent on colonization of new lineages from the continent, as predicted by ecological theory. Evolutionary processes such as in situ diversification are relatively insignificant drivers of both species richness and PD compared with colonization from regional species pools, even over evolutionary time-scales on large islands. [ABSTRACT FROM AUTHOR]