A mathematical model of the impacts of climate change on the winter tick epizootic in moose

Abstract

The winter tick (Dermacentor albipictus) is a cervid-targeting parasite that poses serious conservation concerns for moose (Alces alces) in North America. Described as a greater “enemy” of moose than wolves, bears, and cougars, winter tick parasitism causes moose to excessively groom during nutritionally limited periods, leading to lethal combinations of malnutrition and wound-infections. We construct two mathematical models using ordinary differential equations (ODEs) parameterized by the empirical literature to simulate in silico the seasonal relationships between winter ticks and moose — ultimately producing the first application of mathematical models to this phenomenon. We then use our mathematical models to forecast the stability of this parasitic relationship as season lengths fluctuate due to climate change. Finally, we test the high-risk conservation hypothesis that limited, seasonal harvesting can improve moose population stability in the face of these challenges. Our model identifies the parameters (i.e. select vital rates) that give rise to cyclic and sustained epizootics and suggests that delayed first-frosts due to climate change pose a serious threat to maintaining moose populations, but that moderate winter and/or autumn harvesting strategies can reduce the threat of extirpation and stabilize population trajectories.