Dispersal is more important than climate in structuring turtle communities across different biogeographical realms

Abstract

Aim Ecological communities may be structured by deterministic processes commonly related to climatic conditions or to neutral processes commonly associated with dispersal limitation. This study aims to evaluate the processes responsible for structuring the composition of turtle communities across different biogeographical realms.

Location Global

Methods We used distribution maps of 290 non-marine turtle species to determine the components of beta diversity (turnover and nestedness/richness difference) within the biogeographical realms. We also used a recently published phylogeny to calculate phylogenetic beta diversity. Then, we used partial Mantel tests and multiple regressions on distance matrices (MRM) to evaluate the importance of ecological and spatial factors in determining turtle beta diversity. We also used multiple regressions to evaluate whether temperature instability since the Last Glacial Maximum (LGM) or topographical heterogeneity was the main driver of beta diversity.

Results The beta diversity of turtles in all realms was mainly influenced by the turnover component. However, the nestedness/richness difference component was also important, mainly in realms subject to large climatic variations since the LGM. Environmental distance was positively related to beta diversity in some realms, but this effect was generally low. Geographical distance explained a higher amount of variance than environmental distances in all the realms. Phylogenetic beta diversity provided similar results to taxonomic beta diversity. Temperature instability since the LGM was a strong driver of taxonomic beta diversity in the Nearctic realm, but its effect on the Neotropical realm was mainly concentrated in the turnover component.

Main conclusions Spatial processes such as dispersal may be more important than climatic differences in structuring the composition of turtle communities in the distinct biogeographical realms. However, when climate is also important, the effect of environmental processes such as temperature instability since the LGM and topographical heterogeneity are not the same in the different biogeographical realms.