Effects of the progressive abandonment of grazing on dung beetle biodiversity: body size matters

Dung beetles are an ecologically important group of insect species inhabiting semi-natural grasslands in Europe. Despite their ecological importance, several dung beetle species are currently facing local threats mainly stemming from changes in land use practices, including the abandonment of pasturelands. The aim of this study was to analyze the impact of the progressive abandonment of grazing lands on dung beetle alpha diversity, abundance, biomass and body size classes. Areas representing a range of trophic resource availability were compared: (i) abandoned, (ii) low and (iii) moderate grazing intensity. A total of 136,884 specimens belonging to 56 species (3 Geotrupinae; 16 Scarabaeinae; 37 Aphodiinae) of dung beetle were collected. Pastureland abandonment was shown to lead to a decrease in alpha diversity and biomass density, a reduction of 22 and 78% respectively in abandoned areas. From a biomass standpoint, the effects of pastureland abandonment varied according to the body size classes of the dung beetles, with larger species proving more susceptible to local extinction. Such body-size dependent variations led us to propose the use of both biomass and abundance data in making assessments since they are differentially sensitive to trophic resource availability. Hence, from a conservationist standpoint, the obtained results suggest that traditional pastureland management with low-moderate grazing intensity should be maintained.