The effects of the intensification of agriculture on northern temperate dung beetle communities

Abstract

Summary There is growing concern that the intensification of agriculture within southern Ireland is having detrimental effects on Irish fauna through habitat loss, reduction in biodiversity and pollution‐related events. To assess the impact of farm management on one group of important insects, the dung beetles, their abundance, biomass, diversity and species richness were examined using dung‐baited pitfall traps in intensive, organic and rough grazing farms. We collected 39 631 dung beetles belonging to 24 different species. Eight species (Aphodius prodromus, A. sphacelatus, A. ater, A. rufipes, A. depressus, Sphaeridium lunatum, S. scarabaeoides and Margarinotus carbonarius) accounted for 94% of the captures, but their relative dominance varied with farm type. 54% of total individuals captured were from organic sites, 30% from intensive sites and 16% from rough grazing sites. Organic farms had significantly greater beetle biomass, diversity and species richness compared to intensive and rough grazing farms. Aphodius abundance on organic farms was significantly greater than on intensive and rough grazing farms in spring and autumn. Aphodius biomass on organic farms was significantly greater than on rough grazing farms in spring, late summer and autumn, and greater in autumn compared with intensive farms. A colonization experiment demonstrated that the variation in dung beetle abundance among different dung types depended on the farm type. This was not true for beetle biomass colonizing dung pads, where variation among different dung types and different farm types were independent. Multiple comparisons showed that under rough grazing and intensive management there was significantly greater beetle abundance and biomass found in dung from organic and intensive farms than from rough grazing farms. Dung from organic farms held a significantly greater beetle biomass than the intensive and rough grazing dung. Synthesis and applications. Intensive agricultural management including the use of chemical fertilisers, veterinary drugs (e.g. ivermectin) and removal of herbaceous field boundaries could be detrimental to dung beetle biodiversity and dung decomposition. Organic farming has beneficial effects on dung beetle communities. Patchy ecosystems characterized by a diversity of ungulate species increase dung beetle diversity and hence improve dung decomposition.