Data from: 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
more strongly correlated to the distributions of other colonizers
inhabiting a different continent than to the distribution of sedentary
species. Main conclusions Our results highlight the importance of
historical migrations and dispersal in configuring present-day diversity
gradients. We also suggest that colonizers may be particularly vulnerable
to future climate change because of the predicted disproportionate
decrease in climate space in the extra-tropical realm where they are
currently most diverse.