Large carnivore foraging contributes to heterogeneity in nutrient cycling

Abstract

Context: Carnivores influence the spatial heterogeneity of biogeochemical processes in ecological communities through predation and the deposition of animal carcasses, and these processes may lead to positive feedback loops that influence large-scale patterns of nutrient cycling. Objectives: We assessed whether ambush predator foraging impacted soil chemistry and plant forage quality, and then scaled these effects to the landscape to assess whether carnivores contribute to heterogeneity in resource distributions. Methods: We measured total nitrogen (N) and N stable isotope composition (δ15N) of soils and plants at 172 ungulate carcasses killed by mountain lions in the Yellowstone Ecosystem, USA. We measured kill rates and estimated the probability of a mountain lion foraging in any location to scale their carrion contributions to the landscape. Results: Carcasses altered total nitrogen N and δ15N of soils and plants, and changes in δ15N suggested that plants absorbed significant N from carcasses. On average, plant δ15N at kill sites increased by 2.3 milles (‰), which is large compared to the 6.3 ‰ range of variation in local plants across xeric and mesic systems. We conservatively estimated that resident mountain lions in our study area annually contributed the carrion mass of a blue whale, or 44.1 kg of carrion and 1.4 kg of N per km2. We also determined that mountain lion foraging was concentrated in just 4% of our study system. Conclusions: Ambush carnivore foraging may contribute to landscape-scale heterogeneity in nutrient distributions, and set the stage for positive feedback loops between carnivores and prey that drive biogeochemical processes.