COS 75-2 - Tasmanian devil scavenging influences ecosystem nutrient delivery

Abstract: Scavengers play a critical role in shaping rates of nutrient delivery within ecosystems from carrion. Tasmanian devils (Sarcophilus harrisii) are apex predators in Tasmania and are among the few scavenging species that ingest and process bone material. We therefore expect devils play a unique role in the ecosystem by increasing the availability of bone-derived nutrients, such as phosphorus and calcium, for plant and microbial uptake. However, the emergence of a transmissible and lethal cancer (devil facial tumor disease, DFTD) has led to the rapid decline of devil populations as DFTD spreads from east to west across Tasmania. We evaluated whether DFTD-induced population declines altered rates of carrion decomposition, biogeochemical cycling, and nutrient availability across the devil density gradient.

In July 2022, we deployed 48 carcasses across the DFTD gradient. We manipulated scavenger access by staking carcasses to allow full scavenger access (devils, mesocavengers, invertebrates, microorganisms) or caging them to exclude devils. We then collected paired control and treatment soils across time to test how devil activity (or exclusion) influenced rates of carrion decomposition and nutrient cycling. We collected soil samples from below carcasses and paired control sites and measured shifts in soil nutrient concentrations, pH, electrical conductivity, and microbial community composition via 16S and ITS amplicon sequencing.

We found that carcass consumption (including of bones) was significantly higher at staked carcasses, particularly those consumed by devils. In contrast, devil exclusion increased the length of time carcasses persisted on the soil and the flow of nutrients belowground. Specifically, we found that soil pH and nutrient concentrations (nitrate, ammonium, phosphate) were 1.6 to 12 times higher beneath devil-excluded carcasses. We also present results on how the mode of carcass consumption (e.g., devil versus mesoscavenger and avian) influences bacterial and fungal community composition and assembly. Our results suggest rapid carcass utilization and relocation by vertebrate scavengers dampens the direct effect of carcasses on underlying soils but increases nutrient dispersal across the landscape via excretion. Understanding the impact of scavengers on ecosystem function is critical from an ecological perspective and for aiding conservation strategies, particularly as many apex predators are in global decline.