Mathematical Biology Seminar T.J. Clark-Wolf, Utah State University, Wednesday, October 15, 2025 12:30 pm in LCB 222 Top-Down and Bottom-Up Forces Shape Caribou Population Cycles over Space and Time Abstract: Animal populations rarely remain constant and can oscillate dramatically in response to ecological feedbacks. While population cycles are well documented in small mammals like voles and lemmings, we know far less about whether similar dynamics occur in larger mammals. Caribou show multidecadal booms and busts, but the mechanisms driving these cycles remain unclear, especially under accelerating human-driven environmental change. In this talk, I'll present on my global analysis of caribou dynamics, combining statistical models of empirical data from 43 caribou herds with a tri-trophic mechanistic model that links predators, caribou, and predation. I investigated how top-down and bottom-up forces interacted to shape the period and amplitude of caribou population cycles across broad climatic gradients. My empirical analysis detected long-term population cycles in roughly half of the caribou herds and showed that lower food productivity and colder winters tend to lengthen and intensify these cycles. The mechanistic model replicated these patterns, suggesting that simple feedbacks between food supply and predation can generate complex population cycles in large mammals, similar to those classically observed in smaller species. Together, these results show how coupled theoretical-empirical approaches can reveal processes that regulate population stability and help predict how environmental change may push ecosystems towards more boom-and-bust dynamics. I'll discuss how these models may inform adaptive, dynamic management of caribou populations in a changing world.