Global patterns of β-diversity along the phylogenetic time-scale : the role of climate and plate tectonics

Aim: We aimed to assess the relative influence of the historical and contemporary processes determining global patterns of current β-diversity. Specifically, we quantified the relative effects of contemporary climate and historical plate tectonics on β-diversity at different phylogenetic scales. Location: Global. Time Period: Contemporaneous. Major taxa studied: Mammals and birds. Methods: We analysed the current β-diversity patterns of birds and mammal assemblages at sequential depths in the phylogeny, that is, from the tips to deeper branches. This was done by slicing bird and mammal phylogenetic trees into 66 time slices of 1 Ma (from 0 to 65 Ma) and recording the branches within each slice. Using global distribution data, we defined the branches’ geographical distribution as the union of the corresponding downstream species distributions. For each time slice, we (a) computed pairwise β-diversity across all the grid cells for the whole world and (b) estimated the correlation between this β-diversity matrix and contemporary climatic and geographical distances, and past geological distances, a proxy for plate tectonics. Results: Contemporary climate best explained the β-diversity of shallow branches (i.e., species). For mammals, the geographical isolation of landmasses generated by plate tectonics best explained the β-diversity of deeper branches, whereas the effect of past isolation was weaker for birds. Main conclusions: Our study shows that the relative influence of contemporary climate and plate tectonics on the β-diversity of bird and mammal assemblages varies along the phylogenetic time-scale. Our phylogenetic time-scale approach is general and flexible enough to be applied to a broad spectrum of study systems and spatial scales.