Environmental heterogeneity as a determinant of bee diversity patterns in the Atlantic Forest

The Atlantic Forest encompasses a wide range of environmental and geographical gradients with high endemism and species diversity among several taxonomic groups, including bees. Environmental heterogeneity is a determining factor for species diversity, as environments with greater heterogeneity tend to offer a greater variety of conditions, thus supporting higher species richness. However, bee richness patterns and their relationship with environmental heterogeneity in the Atlantic Forest remain underexplored. In this study, we aimed to describe the bee diversity patterns and investigate how different components of environmental heterogeneity—specifically temperature seasonality, topographic and geomorphic heterogeneity, and stream density—influence species richness, both for the entire biome and within each ecoregion. To do so, we modeled and estimated the distribution of 466 bee species. Relationships between bee species richness and environmental heterogeneity variables were analyzed using Generalized Linear Models, variable importance, and partial dependence curves. We found that the highest richness was in the southwestern regions of the Atlantic Forest, particularly in the Serra do Mar Coastal Forests and Araucaria Moist Forests. The most important variables positively related to species richness were temperature seasonality, followed by topographic and geomorphic heterogeneity, whereas stream density showed the lowest importance. At the ecoregion level, temperature seasonality was the most important variable for 9 of the 11 ecoregions, followed by topographic and geomorphic heterogeneity. In ecoregions with the highest bee richness, environmental heterogeneity showed a low explanatory power. Notably, the relationships between the environmental heterogeneity variables and species richness varied across ecoregions. Our findings highlight the significant role of environmental factors in shaping bee species richness in the Atlantic Forest at multiple scales. Furthermore, the distinct relationship observed between environmental heterogeneity and species richness across ecoregions reinforces the necessity of multi-scale diversity studies to elucidate the unique characteristics of each ecoregion. Bee species richness in the Atlantic Forest is greatest in the south-west and southern regions. Seasonal temperature was the most important variable for predicting species richness, showing a positive effect in nine of the 11 ecoregions. Topographic and geomorphic heterogeneity contributed significantly to species richness in certain ecoregions. Relationship between species richness and environmental heterogeneity variables varied among ecoregions. Ecoregions with higher richness were poorly explained by environmental heterogeneity, suggesting other influencing factors. Multiscale analysis reveals that different regions may have unique species richness drivers, crucial to understanding species diversity in this biodiversity hotspot.