Remotely sensed tree height and density explain global gliding vertebrate richness

In vertebrates, gliding evolved as a mode of energy-efficient locomotion to move between trees. Gliding vertebrate richness is hypothesised to increase with tree height and decrease with tree density but empirical evidence for this is scarce, especially at a global scale. Here, we test the ability of tree height and density to explain species richness of gliding vertebrates globally compared to richness of all vertebrates, while controlling for biogeographical and climatic factors. We compiled a global database of 193 gliding amphibians, mammals and reptiles and created maps of species richness from extent-of-occurrence range maps. We paired species richness of gliding vertebrates with spatial estimates of global tree height and density and biogeographical regions (BGRs) as covariates to account for ecological and historical differences among global regions. We used univariate linear and multivariate generalised linear mixed-effect models to evaluate relationships between species richness and tree height and density, and the interaction between both variables. We found that richness of all gliding vertebrate species increased significantly with tree height, while results for richness of gliding amphibians, mammals and reptiles alone indicated mixed responses especially among different BGRs. Mixed-effect models mirrored these results for richness of all gliding species combined, while also revealing the mixed response to tree height and denisyt of richness of gliding amphibians, mammals and reptiles. Richness of all vertebrate species – gliding and non-gliding – also increased with tree height and density, but at a lesser rate than richness of gliding vertebrates, indicating a greater influence of forest structure on richness patterns of gliding vertebrates. Our results support hypotheses stating that gliding in vertebrates evolved globally in tall forests as energy-efficient locomotion between trees, and provide further evidence for the importance of forest structure to explain the distribution of gliding vertebrates.