Unveiling the drivers of local dung beetle species richness in the Neotropics

Aim: Nearly 40 different hypotheses have been put forward to explain the latitudinal diversity gradient, implying that geographical variations of biodiversity may be the result of a complex array of factors affecting organisms in different ways. Our main goal was to identify the most important drivers of local dung beetle species richness in the Neotropics. Location: Neotropics. Taxon: Dung Beetles (Coleoptera: Scarabaeinae). Methods: We used a multi-model approach to identify which potential drivers correlate better with the variations in local dung beetle species richness. We surveyed published literature on dung beetle communities to extract information on species richness, abundance, type of bait, type of habitat and sampling effort (as hours/pitfall) for different localities, discarding sites with low sampling effort. We used environmental variables to account for six possible explanations of species richness gradients: productivity, water–energy, ambient energy, habitat heterogeneity, resource heterogeneity and seasonality, as well as spatial data to account for other geographically structured phenomena. We used mixed models—with abundance, ecoregion and bait type as random factors—to select the best model among the variables accounting for each explanation. Finally, we used structural equation models to assess which explanations are associated with variations in dung beetle diversity and how they interact. Results: Resource heterogeneity was the best single correlate of dung beetle richness. However, the best multiple model comprises three different explanations: productivity, resource heterogeneity and other spatially structured factors. Structural equation models show that abundance is directly (positively) associated with richness, followed by primary productivity and soil variables (a proxy for environmental heterogeneity), together with mammal richness, (a proxy for resource heterogeneity). Main conclusions: Several explanations need to be considered to account for Scarabaeinae local richness patterns. The diversity of dung beetle communities correlates with the interaction of water–energy dynamics and heterogeneity in both resources and habitats. However, while heterogeneity variables are directly associated with richness, energy relates with it through abundance, and water through resource diversity.