Severe simplification of the structure of dung beetle assemblages in neotropical soybean croplands regardless of the native vegetation domain

The conversion of native vegetation into agricultural areas is arguably the key driver of biodiversity declines globally. We assessed the responses of dung beetle assemblages (Coleoptera: Scarabaeidae: Scarabaeinae) to the effects of native vegetation conversion into soybean monoculture in different vegetation domains (Amazonian forest, scrubland savannahs and transitional vegetation) in the world's largest tropical soybean (Glycine max L.) agricultural frontier. We also assessed the effects of landscape variables (amount of native habitat and amount of pasture) and land use history (time of land use change including soybean cultivation and cattle pastures). We sampled dung beetles at 100 study landscapes throughout the state of Mato Grosso, Brazil, within a region encompassing Amazonian forests, the drier Cerrado savannahs, and transitional vegetation domain between these biomes. In total, we recorded 71,043 individuals of 165 species, with 39,090 individuals (155 species) sampled in native vegetation and 31,953 individuals (75 species) in soybean monoculture areas, 30 species of which could persist in croplands. We found differences in species composition, and lower species richness, overall abundance and biomass in monoculture areas, compared to adjacent native habitat. Time since land-use change into pasture was the main determinant of species richness and species compositional similarity in monocultures, while none of the landscape and land use history variables were informative in explaining overall abundance. We provide clear evidence that the conversion of native vegetation into soybean monoculture negatively affects dung beetle assemblages. Furthermore, croplands harboured their own unique dung beetle assemblages containing species typical of open-habitats and pasturelands, which are likely tracking the historical advance of the agricultural frontier. However, species typical of forest environments were most detrimentally affected and were largely missing in cropland areas.