Large carnivore competition and predation dynamics in northern Yellowstone

Abstract

Competition and predation are the most fundamental of species interactions, driving animal behavior, evolution, population dynamics, and, ultimately, the structure and function of ecosystems. Interactions between large carnivores and with their prey can have disproportionately large effects on ecosystem processes due to their position at the top of food chains. However, identifying the causal mechanisms underlying these interactions, and the impact they have on community structure, is complicated by the dynamic, context-dependent nature of species and ecosystems. In other words, no species interaction is created equal. Long-term research provides an avenue to tease apart these interactions and develop a more comprehensive understanding of communities to better inform the conservation and management of diverse ecosystems. I use a blend of camera-trap data and long-term wolf (Canis lupus) and cougar (Puma concolor) radio-collar data from northern Yellowstone National Park, USA to develop a more nuanced, mechanistic understanding of how competition and predation unfold in natural systems. First, I used predation data collected from visiting wolf and cougar GPS-location clusters during 2016–2022 to show that our ability to predict predation versus non-predation events is contingent upon variations in season, predator and prey characteristics, and the modeling approach used. Predation patterns were more easily predicted for a solitary carnivore with high fidelity to kill sites (cougar) than for a social carnivore that consumes prey faster (wolf) in winter when prey was larger than in summer, and when using machine learning models compared to traditional generalized linear models. Second, I used 23 years of predation data collected from VHF- and GPS-collared cougars during 1987–2022 to document the causes and consequences of kleptoparasitism of cougar kills by dominant wolf and bear (Ursus spp.) competitors. Counterintuitive to conventional theory, even as carnivore densities increased and primary prey availability declined over the long-term, interference competition at cougar kills declined. By also accounting for long-term declines in the size of cougar-killed prey, I illustrate how lesser-studied factors like prey size can have dramatic effects on competition and predation dynamics, and in this case, promote coexistence of North America’s most diverse large carnivore community. Finally, I use apex (wolf and cougar) and mesocarnivore (red fox (Vulpes vulpes) and coyote (Canis latrans)) detections from camera-trap data collected during 2020–2023 and apex carnivore predation data from 2016–2023 to demonstrate how the behavior and ecology of different carnivores shapes unique risk-reward landscapes for mesocarnivores co-occurring with apex carnivores.