Uncovering how traits have shaped the global biogeography of tetrapods

Dispersal across biogeographic barriers is a key process determining global patterns of biodiversity as it allows lineages to colonise and diversify in new realms. However, biogeographic dispersal is rare and difficult to observe, so we know little about its determinants. While species’ traits are assumed to be linked to the success of dispersal and establishment to far-away locations, this has not been tested at large scales and across different taxonomic groups. Here, we demonstrate that past biogeographic dispersal events often depended on species’ traits by analysing 7009 tetrapod species in 56 clades. Incorporating body size or life history into biogeographic models improves model performance in 91% of clades and leads to an increase in dispersal rates of 28-32% for lineages with disperser traits. Differences between clades in the effect magnitude of life history on dispersal rates are linked to the strength and type of biogeographic barriers (continental/oceanic), and intra-clade trait variability. In many cases, large body sizes and fast life histories facilitate dispersal success, as expected by theory. However, small and/or species with slow life histories, or those with average traits, have an advantage in a significant minority of clades, with body size-dispersal relationships depending on a clade’s average body size and life history strategy. These results provide important new insight into how traits have shaped the historical biogeography of tetrapod lineages and may impact present-day and future biogeographic dispersal.