Where water meets rock: Ecological niches and diversity hotspots of hygropetric beetles in the Neotropics

Abstract

Freshwater biodiversity is structured by climate and topography controls on moisture at fine scales. Hygropetric habitats (thin water films over rock) remain underrepresented in macroecology. We tested whether major Neotropical areas occupy distinct environmental space, whether hygropetric beetle genera show low niche overlap, and quantified richness in mountainous and topographically steep regions. We assembled 144 species in 15 genera across seven families from taxonomic literature, GBIF and targeted field sampling at 97 waterfalls and streams in the Brazilian Shield, including 66 new occurrences. Species distribution models, using five algorithms and predictors that included bioclimatic variables, elevation, compound topographic index and profile curvature, were cross-validated. Multivariate analyses compared environmental space among provinces, and niche overlap metrics assessed intergeneric segregation. Major Neotropical areas occupied significantly different environmental space, and genera formed ecologically distinct groups with low niche overlap, indicating environmental partitioning and some convergence onto similar moisture and energy regimes across disjunct regions. Mountainous areas were richness hotspots, with Brazilian Shield representing 40% of species richness, Guiana Shield 33%, Andes 19% and Northern Neotropics 8%. Significance: Integrating macroecology, niche modelling and new field data yields a scalable approach to forecasting hygropetric biodiversity. It closes key knowledge gaps for Neotropical beetles and improves planning for freshwater biodiversity conservation.