Water table level and soil texture are important drivers of dung beetle diversity in Amazonian lowland forests

The high biodiversity of the Amazon region is related to variation in soil physical properties and water-table depths. Dung beetles are efficient bioindicators that feed and breed on the soil surface and below ground, affecting soil properties and being affected by them. Here, we investigate the influence of soil physical characteristics (proportions of sand, silt, clay) and water-table depth on dung beetle assemblages and functional groups in a forest in central Amazonia. We sampled beetles in 29 transects with different soil physical properties and water-table maximum levels, and analyzed beetle species richness, abundance and species composition for the total assemblage and for each functional group (rollers, tunnellers, dwellers). Dung beetle abundance increased with soil clay content (GLMM; p = 0.009) whereas dweller (GLMM; p = 0.017) and tunneller species richness increased with clay and silt contents (GLMM; p = 0.018). Sites with deeper water table had greater roller-beetle abundance (GLMM; p = 0.049). Dung beetle assemblage composition was strongly influenced by clay content. Our results suggest that soil texture and water-table levels determine dung beetle distributions, both for the whole assemblages and for each functional group separately. These findings highlight the role of soil structure in determining dung beetle assemblages.