PS 40-101 - Exploring the role of scavenger declines on soil chemistry, microbial composition, and ecosystem function

Abstract: Top scavengers are essential to food web structure, and their population declines have cascading effects on the trophic levels below them. Tasmanian devils are apex scavengers endemic to the island of Tasmania and have the unique ability to rapidly return carcass (and bone)-derived nutrients to the environment, with likely impacts to soil biogeochemistry and biological productivity. However, a highly transmissible and extremely lethal cancer (devil facial tumor disease; DFTD) is threatening devil populations across roughly 95% of their habitat. Since 1996, the east to west spread of DFTD has created a spatiotemporal gradient in devil population density. The resulting devil density gradient provides a rare opportunity to investigate how the decline of top scavengers affects the rate of nutrient cycling from carcasses to soils and whether these dynamics shift microbial community composition and ecosystem function. Here, we tested whether devil population declines across the gradient altered belowground nutrient cycling and microbial community composition. We collected soil samples from eucalyptus forests spanning the devil density gradient and measured soil moisture and pH, extractable pools of dissolved organic carbon (DOC) and nitrogen (TDN), and bioavailable pools of nitrate (NO₃^-), ammonium (NH₄⁺), and phosphate (PO₄⁺). We extracted microbial DNA, quantified microbial biomass, and characterized bacterial and fungal community composition via amplicon sequencing of the bacterial/archaeal 16S gene and the fungal ITS1 region. We assessed changes in soil biogeochemistry and microbial community composition with respect to the devil population gradient using linear mixed effects models. We found that soil pH declined from east to west across the DFTD gradient but was likely driven by an increasing precipitation gradient across the island and weathering of soil parent material. We observed variable patterns among soil characteristics, with some increasing in concentration with greater devil density (e.g., DOC, NH₄₊₎ and others decreasing (e.g., NO₃^-). The changes in soil characteristics and biogeochemical processes furthermore appeared to accompany shifts in microbial community composition. Overall, our study identified significant variation in soil biogeochemical properties and microbial communities across the devil density gradient. Our future work focuses on the direct impact of Tasmanian devils and other mesoscavengers on rates of carrion decomposition with the goal of identifying how dominant scavengers influence soil nutrient cycling and forest ecosystem function.