Species-rich dung beetle communities buffer ecosystem services in perturbed agro-ecosystems.
Many studies document high levels of functional redundancy in ecosystems, suggesting that species extinctions will not be detrimental to ecosystem functions and services. However, apparently redundant taxa may prove critical for sustaining ecosystem functions and services in the context of environmental perturbations. Dung beetles (Coleoptera:Scarabaeidae) provide a valuable ecosystem service in temperate agro-ecosystems by increasing rates of dung decomposition and nutrient cycling. However, there is concern that these services may be negatively affected by changes in species richness and composition due to changes in pasture management and negative effects of anthelmintics used to control livestock parasites. We used a mesocosm experiment to investigate the functional importance of dung beetle species richness in a system perturbed by the anthelmintic, ivermectin. We varied dung beetle species richness within three functional groups in factorial combination with ivermectin treatment. In the short term (1-4 weeks), multi-species dung beetle assemblages achieved higher decomposition rates than monocultures, but only in ivermectin-treated dung. Varying species-specific sensitivities to ivermectin meant that species-rich assemblages sustained ecosystem functioning in the context of this anthropogenic perturbation. Over the longer term (36 weeks), there was a significant, positive effect of species richness on dung decomposition in both ivermectin-treated and untreated dung, underlining the functional importance of maintaining a species-rich dung processing community even in the absence of perturbations to the system. Synthesis and applications. The interacting effects of dung beetle species richness and ivermectin highlight the importance of maintaining diverse assemblages in the face of anthropogenic perturbations and suggest that apparent functional redundancy of species in agro-ecosystems should be interpreted cautiously. Furthermore, different farm management practices (e.g. pesticide use and fragmentation of habitats) may have consequences for ecosystem functions and services that exceed the effects of each when considered in isolation.