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

• Main Authors: Morales-Castilla, Ignacio, Davies, Jonathan T, Rodríguez, Miguel Ángel
• Format: Other/Unknown Material
• Language: unknown
• Published: PeerJ 2018
• Subjects: Bering Land Bridge
• Online Access: http://dx.doi.org/10.7287/peerj.preprints.26440; https://peerj.com/preprints/26440.pdf; https://peerj.com/preprints/26440.xml; https://peerj.com/preprints/26440.html

Successful explanations for diversity gradients should account for both the generalized tendency towards a higher tropical diversity and its exceptions. Moreover, identifying exceptions to general trends, such as the latitudinal diversity gradient can give insight into the mechanistic explanations responsible for structuring them. The Cenozoic biotic exchange of mammals across the Bering land-bridge provides an illuminating case-study. It allows comparing the diversity of clades that participated in the exchange (colonizers), whose ancestors withstood the Beringian cold temperatures, with that of the clades that did not participate (sedentaries). 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, the geographic distribution of colonizers is more strongly correlated to the distributions of other colonizers inhabiting a different continent than by the distribution of sedentary species. These results highlight the importance of historical migrations and dispersal in configuring present-day diversity gradients. Importantly, we also suggest that colonizers may be particularly vulnerable to projected climate change because of the predicted decrease in climate space in the extra-tropical realm where they are currently most diverse.