Elevational diversity patterns of rodents differ between wet and arid mountains

Aim: Patterns of species richness along elevation gradients vary with geographic and environmental factors but evidence for similar variation in functional and phylogenetic diversity remains scarce. Here, we provide the most comprehensive evaluation to date of elevational gradients in taxonomic, functional, and phylogenetic diversity of rodents - one of the most ecologically diverse groups of mammals - and test the effects of latitude and aridity on their variation for the first time. Location: Forty-nine mountains on five continents. Time period: Contemporary. Major taxa studied: Rodents (Rodentia). Methods: We compiled elevational distributions of 374 rodent species across 49 elevational gradients. For each gradient, we quantified - in 100-m elevational bins - rodent species richness and functional and phylogenetic richness, evenness, and dispersion, and their species richness-corrected equivalents. To assess how rodent diversity varies with elevation, we fitted a series of models that included elevation, average latitude, and aridity of each mountain system while accounting for variation in study design and sampling effort. Results: A common mid-elevational peak in species richness among mountains contrasts with functional and phylogenetic diversity pattern variation (model shape and slope) explained by the aridity at a mountain's base. Specifically, we find that functional and phylogenetic richness and dispersion decline with elevation in wet mountain systems but increase with elevation in arid mountains. Main conclusions: In this first comparative analysis of mammal functional and phylogenetic elevational gradients, we find that the decoupling of each from species richness is particularly pronounced in arid regions. Wet-mountain lowlands and arid-mountain highlands harbour the most functionally and phylogenetically diverse rodent communities, indicating that water availability is a strong environmental filter in structuring diversity of small mammals on mountain gradients. High regularity of species distances within assemblages supports a constant role for competition across all elevations and niche expansion in elevations with greater species richness.