Mass mortality events (MMEs), in which large numbers of animals unexpectedly die in a short period of time, have been increasing in frequency. The carcasses produced by these events are an enormous resource pulse for scavengers and decomposers. However, the unpredictable nature of MMEs makes them difficult to study, and little is known about their community and ecosystem impacts. In July 2016, we simulated MMEs using feral swine (Sus scrofa) carcasses to experimentally investigate the effects of MMEs. At each of five sites, we established four 18m2circular plots, which were randomly assigned to treatments in a factorial design that crossed carcass addition (yes or no) and vertebrate scavenger access (open or wire exclosure). Sites were randomly assigned to one of five biomass treatments (25, 60, 180, 360, 725 kg per plot), with more than 2700 kg of carcasses used in the whole experiment. We monitored carcass decomposition rates as well as vertebrate, insect, microbial, and plant communities to evaluate their responses to carcass additions. Additionally, we tested the hypothesis that vertebrate scavengers ameliorate the effects of MMEs on decomposition and communities by removing biomass from carcasses.
Carcasses had significant effects on vertebrate, insect, and plant communities, as well as soil properties. We found an interactive effect of biomass treatment and vertebrate exclosures, indicating that the effect of vertebrate scavengers increased with carcass biomass. Excluding vertebrate scavengers reduced decomposition rate and significantly increased abundance of carrion flies, probably by reducing competition for carcasses and consumption of fly larvae. The experiment is ongoing, and specific results from microbial analyses and measurements of resilience are pending. However, our initial results are consistent with the hypothesis that MMEs have nonlinear effects on ecosystems and that vertebrate scavengers (e.g., vultures) reduce the impacts of MMEs.