Global patterns of functional trait variation along aridity gradients in bats

Aim Our understanding of the biological strategies employed by species to cope with challenges posed by aridity is still limited. Despite being sensitive to water loss, bats successfully inhabit a wide range of arid lands. We here investigated how functional traits of bat assemblages vary along the global aridity gradient to identify traits that favour their persistence in arid environments. Location Global. Time period Contemporary. Major taxa studied Bats. Methods We mapped the assemblage-level averages of four key bat traits describing wing morphology, echolocation and body size, based on a grid of 100-km resolution and a pool of 915 bat species, and modelled them against aridity values. To support our results, we conducted analyses also at the species level to control for phylogenetic autocorrelation. Results At the assemblage level, we detected a rise in values of aspect ratio, wing loading and forearm length, and a decrease in echolocation frequency with increasing aridity. These patterns were consistent with trends detected at the species level for all traits. Main conclusions Our findings show that trait variation in bats is associated with the aridity gradient and suggest that greater mobility and larger body size are advantageous features in arid environments. Greater mobility favours bats' ability to track patchy and temporary resources, while the reduced surface-to-volume ratio associated with a larger body size is likely to reduce water stress by limiting cutaneous evaporation. These findings highlight the importance of extending attention from species-specific adaptations to broad scale and multispecies variation in traits when investigating the ability of species to withstand arid conditions.