The predatory impacts of invasive European wasps on flies are facilitated by carcasses with open wounds

Abstract

Carrion is a vital resource in terrestrial ecosystems, supporting complex networks of interacting consumer organisms. The insect community attending carrion forms a vital part of this food web, but the functional roles of insects as scavengers can be altered by invasive species via the effects of predation and competition. European wasps (Vespula germanica) have invaded many parts of Australia and have been documented to directly kill native insect scavengers, especially necrophilous flies. Yet, little is known about the factors that influence predation rates by European wasps on flies at carcasses. The aim of this study was to determine how carcass state and altitude influences the occurrence and predatory impacts of wasps on flies. We placed 18 kangaroo carcasses along an altitudinal gradient in an Australian alpine ecosystem and manipulated half of the carcasses by splitting them open to simulate the wounds created by vertebrate scavengers present at the time of death. We found that carcasses with open wounds exacerbated already severe predation on flies from wasps, as well as intense scavenging activity, even though wasp abundance remained the same across both treatments. Meanwhile, densities of wasps declined and their impact on flies lessened with higher altitude. We suggest that the suppressive effect of wasps on flies may interrupt key processes triggered by carrion and cause shifts in energy flow through scavenger food webs. Further, under climate change, we predict that wasps will continue to spread into new areas at altitudes the species currently find unhospitable and conclude that carcass management practices must recognise the potential threat that wasps pose to ecosystem stability.