Effect of dung beetle species richness and chemical perturbation on multiple ecosystem functions

1. The relationship between biodiversity and ecosystem functioning is typically positive but saturating, suggesting widespread functional redundancy within ecological communities, However, theory predicts that apparent redundancy can be reduced or removed when systems are perturbed, or when multifunctionality (the simultaneous delivery of multiple functions) is considered. 2. Manipulative experiments were used to test whether higher levels of dung beetle species richness enhanced individual functions and multifunctionality, and whether these relationships were influenced by perturbation (in this case, non-target exposure to the veterinary anthclmintic ivermectin). The four ecosystem functions tested were dung removal, primary productivity, soil faunal feeding activity and reduction in soil bulk density. 3. For individual functions, perturbation had limited effects on functioning, with only dung removal significantly (negatively) affected. Species richness did not, on its own, explain significant variation in the delivery of individual functions. In the case of primary productivity, an interaction between richness and perturbation was found: species-rich dung beetle assemblages enhanced forage growth in the unperturbed treatment, relative to the perturbed treatment. 4. Using a composite 'multifunctionality index' it was found that species-rich dung beetle assemblages delivered marginally higher levels of multifunctionality in unperturbed conditions; however, this benefit was lost, under perturbation, Using a relatively new and robust method of assessing diversity multifunctionality relationships across a range of thresholds, no significant effect of species richness on multifunctionality was found.