Predation and scavenging mediate nutrient cycling and distribution in the high Andes

Julia Monk and Oswald J. Schmitz, School of the Environment, Yale University, New Haven, CT, Emiliano Donadio, Rewildling Argentina, Buenos Aires, Argentina

Background/Question/Methods
Animal carcass decomposition is an often-overlooked component of nutrient cycles. The importance of carcass decomposition for increasing nutrient availability has been demonstrated in temperate ecosystems, but impacts in aridlands are poorly understood. In San Guillermo National Park, Argentina, puma predation has historically accounted for nearly all adult vicuña mortality, and thus predation has been the main driver of carcass distribution in this high desert ecosystem. Here, we collected and analyzed samples at puma kill sites across three habitats (plains, canyons, and wet meadows) to evaluate the impacts of carcass decomposition on soil and plant nutrients. We tested two alternative hypotheses: 1) that carcasses would create biogeochemical hotspots with elevated soil and plant nutrients; or 2) that carcasses would have little effect on nutrient levels due to high levels of scavenging by Andean condors. We also hypothesized that vicuña stomachs, which pumas remove from carcasses prior to consuming their kills and which are largely ignored by scavengers, would impact soil and plant nutrients regardless of scavenging.
Results/Conclusions
We found that both hypotheses were supported and depended on habitat type. Soil beneath both carcasses and stomachs had significantly higher soil nutrients than soil from adjacent reference sites in arid plains and canyons, but not in wet meadows, where high moisture and nutrient availability may have overwhelmed any carcass effects. Stomachs had larger effects on soil nutrients than carcasses, and the effects of carcasses were more pronounced in canyons than in plains. Together, these results suggest that scavenger activity, which is highest at carcasses in the plains, may mediate the impacts of predation and carcass decomposition on soil nutrients. Increases in N availability beneath carcasses and stomachs did cascade up to impact plant C:N, but these effects were muted. Overall, the biogeochemical effects of puma kills persisted for several years, indicating that kills do not only create ephemeral nutrient pulses, but can have lasting effects on the distribution of soil nutrients. Comparison to broader spatial patterns of predation risk and nutrient availability reveals that puma predation of vicuñas likely has long-lasting effects on the rate and spatial distribution of nutrient cycling at the landscape scale. Predation and carcass decomposition may thus be important overlooked factors influencing ecosystem functioning in arid environments.