Interactive effects of rangeland management and rainfall on dung beetle diversity

Insects perform many ecosystem functions, yet their responses to disturbance can be unpredictable. Changes in climate may interact with land use disturbances, and given that arthropod species diversity, abundance, and traits within assemblages vary with habitat structure and climatic variables, ecological function may be impaired. Here, we assessed how dung beetle species richness, abundance, functional diversity, mean body size and body size inequality (which can signal assemblage stress responses) varied with climatic, management and habitat variables on livestock farms and protected areas across a rainfall gradient (138–381 mm/year) in arid/semi-arid shrubland (Karoo, South Africa, an area for which entomological biodiversity is relatively poorly known), during a prolonged drought. Species richness was similar between farms and protected areas, but abundance was greater in protected areas. Farms tend to be dominated by sheep in this region, and the type of dung and paucity of dung diversity, along with use of anthelmintics may explain this reduced abundance. Species richness and abundance increased with mammalian herbivore stocking rates and rainfall. Most recent rainfall best predicted species richness, but abundance was best explained by the long-term measure of rainfall (Mean Annual Precipitation). Functional diversity showed no patterns with the environmental or management variables we measured. Mean body length and size variation did not differ between protected areas and farms, but the spread of beetle sizes was more even as vegetation cover increased and soil clay content decreased. Future climate projections indicate extreme declines in rainfall in this area, and our results suggest that this would dramatically impact dung beetle communities. Maintaining vegetation cover may help mitigate effects of climate change.