Aridity Drives Climatic Specialization and Phylogenetic Clustering in Terrestrial Vertebrates

Arid environments constitute one of the main terrestrial biomes on Earth and are predicted to expand under ongoing climate change. Studying the effect of arid conditions on biodiversity patterns and ecological dynamics is therefore critical to understand the evolutionary fate of desert-adapted faunas. Here we provide a global assessment of how aridity influences climatic niche breadth and phylogenetic structure across terrestrial vertebrates. Using distributional data for over 34,000 species of amphibians, squamates, birds, and mammals, combined with environmental data and nearly complete phylogenies of these clades, we quantified species positions along aridity gradients and their climatic niche breadth, and evaluated phylogenetic clustering at multiple spatial scales. Across all groups, species occupying more arid environments exhibited significantly narrower climatic niches than those from non-arid habitats, supporting the hypothesis that ecological filtering in deserts promotes climatic specialization. Further, analyses of system-wide community phylogenetic structure revealed significant phylogenetic clustering in most arid systems for all clades except birds, underscoring that deserts broadly act as ecological filters at large scale, but this effect is subjected to clade-specific traits. However, finer-scale analyses showed significant phylogenetic overdispersion in several cases, suggesting that competition and micro-niche dynamics might be stronger determinants of phylogenetic structure at the local-to-regional level. Together, our results demonstrate that drylands act as ecological filters shaping both functional and evolutionary dimensions of biodiversity, with implications for predicting biotic responses to desertification and climate change.