Latitudinal gradients in African mammal dispersal limitation

Background/Question/Methods

The dispersal-ecological specialization hypothesis posits that trade-offs between dispersal ability and ecological specialization drive latitudinal patterns of species richness. If dispersal limitation has a stronger effect on tropical species, then we expect the turnover in species composition (beta diversity) to be greater with increasing proximity to the equator. Moreover, we expect this relationship to be mediated by functional traits relevant to dispersal (e.g. locomotor adaptations, substrate use). We evaluated the relative influence of dispersal limitation on large mammal assemblages across continental Africa.

Presence-absence data and species attribute data for 260 mammal species at 206 sites across Africa were compiled from published literature sources. Environmental data (temperature, rainfall, elevation) and geographic coordinates were also collected for these sites. We used the Jaccard Index to measure community similarity based on 1) species composition and 2) species traits. We then conducted cluster analysis to identify biogeographic regions across Africa containing sites with similar communities of species. Finally, we performed partial Mantel tests on community similarity in each of 13 regions to determine the relative influence of environmental conditions and geographic distance between sites. 

Results/Conclusions

Results revealed latitudinal gradients in the strength of dispersal limitation. Large mammal assemblages in regions closer to the equator were more strongly structured by dispersal limitation whereas assemblages that were increasingly distant from the equator were more strongly structured by environmental factors. We found consistent patterns when we defined community composition by species or by traits. These results are consistent with the dispersal-ecological specialization hypothesis and suggest that further consideration of the relationship between dispersal ability and species richness is warranted.