From lowlands to highlands: how elevation and habitat complexity drive anuran multidimensional diversity?

Background: Montane environments in Neotropical regions are known for their rich diversity of amphibians, but the ecological drivers behind this diversity along altitudinal gradients remain poorly understood. We investigated the effects of the altitudinal range and local environmental variables on the taxonomic, phylogenetic, and functional alpha and beta diversity of anuran assemblages along an altitudinal gradient in the Atlantic Forest of northeastern Brazil.

Methods: We characterized the richness, abundance, taxonomic, functional, and phylogenetic diversity of anurans in 24 transects within the interior of the forest along an altitudinal range of 200-950 m in the Private Reserve of Natural Heritage (RPPN) Serra Bonita, southern Bahia state, northeastern Brazil. For each transect, we measured the following environmental variables: altitude, leaf litter depth and cover, canopy opening, number of tank-bromeliads, number of trees, and mean air temperature.

Results: We found 36 anuran species distributed in 10 families. Altitudinal strata plays an important role in explaining anuran abundance, with direct-developing frogs being the most abundant species. The number of tank-bromeliads was interpreted as having the most substantial support to explain the anuran abundance, lineage richness and functional diversity, whereas leaf litter depth influenced the dominant lineages. Additionally, altitude significantly influenced taxonomic and phylogenetic dissimilarity. Lastly, we found an inverse pattern of altitudinal Rapoport's rule, in which species with optimal altitudes in the highlands exhibit a lower range-size distribution, likely due to habitat specialization or micro-endemism at higher altitudes.

Conclusion: Altitude significantly influenced the abundance, taxonomic composition, and phylogenetic diversity of anuran communities, with higher elevations supporting a greater number of individuals and distinct evolutionary lineages. In contrast, functional diversity did not vary with altitude, suggesting functional redundancy, where different species perform similar ecological roles, thereby maintaining community resilience. Local factors, such as the number of tank-bromeliads and leaf litter depth, were also key variables shaping community structure. Given the high species turnover and the presence of unique evolutionary lineages, especially in the highlands, conservation efforts should prioritize the protection of the entire montane habitat to sustain the ecological and evolutionary processes that support this exceptional biodiversity. Understanding how species are distributed and identifying the most important filters of anuran diversity along altitudinal gradients in the Atlantic Forest is essential for developing management plans and conservation actions in this threatened region that harbors one of the world's most remarkable assemblages of anurans.