COS 225-5 - Decline of an apex scavenger modifies scavenging communities and reduces the rate of carrion consumption

Abstract: Across the globe, many apex predators and scavengers are in decline. Much research has illustrated how the decline of apex predators can have cascading effects on primary producers through changes in prey abundance and behavior. However, there is still a limited understanding of how declines in apex scavengers influence scavenging communities and carrion decomposition. This lacuna is important because many apex predators are also dominant scavengers. The decline of apex predators could therefore have currently unappreciated effects on scavenging food webs and nutrient delivery within ecosystems. We evaluated if the rapid decline of an apex predator and scavenger, the Tasmanian devil (Sarcophilus harrisii), due to Devil Facial Tumor Disease (DFTD) altered the nature and rate of carcass consumption. We tested our hypothesis that devil declines lead to increased presence of invertebrate scavengers at carcasses and decreased rates of carcass consumption by experimentally manipulating devil access to 48 carcasses deployed across the DFTD gradient in Tasmania. We found that the rate of carcass consumption increased positively with devil density. The average proportion of the carcass consumed after 26 days was 48.4% greater in regions with the highest devil densities than regions with the lowest densities. Across the DFTD gradient, devil exclusion led to a 23.9% increase in the presence of invertebrate scavengers at carcasses. We also present results on the effects of devil declines on the foraging behavior of vertebrate mesoscavengers. Taken together, our results suggest that the decline of apex scavengers can lead to increased carcass consumption by invertebrate scavengers but may ultimately reduce the efficiency of carrion consumption. Hence, global declines in carnivores that are dominant scavengers may generate cascading effects on the nature and rate of nutrient delivery in ecosystems through carrion decomposition.