Aridity drives the loss of dung beetle taxonomic and functional diversity in three contrasting deserts

[Aim]: Aridity gradients are of great interest for understanding the responses of biodi-versity to water availability and water stress. However, little is known about the re-sponses of many animal groups, which are crucial for assessing the effects of climate change. Here, we study the effects of aridity on dung beetle communities, a group with well- known responses to large-scale environmental gradients.[Location]: Sahara, Kalahari and Chihuahuan deserts. [Taxa]: Dung beetles of the family Scarabaeidae.[Methods]: We conducted standardized surveys along approximately 400 km aridity gradients in each of the three deserts, and measured species richness, abundance, evenness and three aspects of trait- based functional diversity (functional richness, functional evenness and functional dispersion). By using randomization tests and linear mixed models, we compared observed with expected values for functional di-versity indices from null models that hierarchically incorporate additional assembly constraints.[Results]: Overall, we found a decrease of both taxonomic richness and functional dispersion along the three aridity gradients. Also, aridity seems to have mild effects on functional richness and functional evenness. Besides these general trends, we identi-fied differences between deserts in the responses of both taxonomic and functional diversity.[Main conclusions] Aridity shows greater importance than competition and other processes of limiting similarity or stochastic processes in community assembly. Also, the functional hypervolume of dung beetle desert communities decreases with aridity not only due to species loss, but also because of selection of a few distinct phenotypes under harsh environmental conditions. Last, we observed that the different regional pools respond to aridity in different ways. Therefore, understanding future responses of dung beetle communities to the progressive decreases in water availability driven by climate change requires determining how the characteristics of the species in the regional pool interact with aridity-driven assembly processes.PCS-B was supported by CSIC grant JAE INT20_EX_0337, and IdeC-A by the Spanish Ministry of Science and Innovation FPI grant BES-2012-054353. This work is part of project SCENIC (grant PID2019-106840GB-C21 funded by MCIN/AEI/10.13039/501100011033), and fieldwork was supported by project SCARPO (grant CGL2011-29317 funded by Spanish MINECO).Peer reviewe