Decline of an apex vertebrate scavenger increases carrion use by invertebrates

Apex consumers are declining worldwide. While the effects of apex predator declines on ecosystems are widely documented, the cascading effects of apex scavenger declines are poorly understood. We evaluated whether disease-induced declines of an apex scavenger, the Tasmanian devil (Sarcophilus harrisii), increased carrion use by invertebrate scavengers. We manipulated devil access to 36 carcasses across a gradient of devil density from east to west Tasmania and measured carcass use by invertebrates. We found the amount of carcass removed within 5 days was 3.58 times lower at sites with the lowest devil densities. Adult carrion beetle (Ptomaphila lacrymosa) and blow fly (Calliphoridae) larvae abundances were two times higher at open-access carcasses at low-density sites than at intermediate- and high-density sites. Adult beetles persisted for 10 days at the low-density site but declined after 5 days when devils had access to carcasses in intermediate- and high-density sites. Blow fly larvae abundance was not affected by devils in the low-density site but decreased with devil access in intermediate- and high-density sites. Our results suggest that apex scavenger declines may increase invertebrate scavenger abundance and their contribution to carrion decomposition, with potential cascading effects on nutrient cycling and ecosystems.