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

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 the Brazilian Shield representing 40%
of species richness, the Guiana Shield 33%, the Andes 19%, and the
Northern Neotropics 8%. 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.