Historical contingency, niche conservatism and the tendency for some taxa to be more diverse towards the poles

Aim We test the ability of the biotic exchange across the Bering land-bridge coupled to niche conservatism to explain current day mammalian diversity gradients. Location the Holarctic Taxon mammals Methods We compared the diversity within clades that participated in the exchange (colonizers), whose ancestors withstood the Beringian cold temperatures, with that within clades that did not participate (sedentaries). We contrasted biogeographical patterns, tested the ability of environmental models to predict species richness of colonizers and sedentaries across continents and, compared richness-climate relationships between colonizers and sedentaries controlling for phylogenetic effects. Results We find that assemblages of colonizers are more diverse towards higher latitudes, opposing the traditional latitudinal diversity gradient which is followed by sedentaries. Despite the long passage of time since this major dispersal event, we find that the geographic distribution of colonizers is mo...