Ecosystem restoration aims to establish biodiverse communities that also contribute to ecosystem functions. Although terrestrial restoration projects often involve the re-establishment of native plant communities, other taxonomic groups usually re-colonize without intervention of assistance. Management activities in restored systems may affect this re-colonization, with important consequences for the diversity and composition of the resulting community and its role in ecosystem function. In restored grasslands, fire and large grazing mammals are both used as management tools to maintain plant physiognomy and diversity, but their impacts on consumers are less understood. One potentially important functional group are dung beetles that process large mammal dung and thus play an important role in nutrient cycling. We investigated the impacts of grazers and fire on dung beetle communities and function in restored tallgrass prairies. We surveyed dung beetle communities in sites that differed in bison presence and application of fire, including thirteen restored prairies, two remnants, and an agricultural field. We also measured dung decomposition in two experiments in these sites. In the first, all dung samples were open, and in the second each sample was paired with an insect-exclusion sample to calculate the effects of insects on decomposition.
We documented five species of dung beetles across all study sites, although 96% of individuals belonged to two species in the genus Onthophagus. Total dung beetle abundance was greater in restored prairies with bison present, but abundance was not affected by prescribed fire. There was a weak trend for greater abundance in older restored prairies. In the first dung decomposition study, dung decomposition as slightly greater in sites with bison but not affected by other environmental variables. In the second experiment, dung decomposition was significantly greater for open samples than for cages samples, indicating that insects play a role in decomposition, but this was no influenced by bison presence or other variables. Although dung beetles are more abundant in the presence of bison, the greater abundance of dung as a resource may dilute their effects so that dung processing rates and decomposition do not differ between sites with and without bison. Nonetheless, these insects have responded quickly (less than two years since bison reintroduction) and appear to be contributing to dung decomposition as an ecosystem function. Future research will investigate how changes in the structure of these communities influences decomposition rates and nutrient cycling rates.