Theoretical Impacts of Habitat Loss and Generalist Predation on Predator-Prey Cycles
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Certain herbivores and their predators undergo high amplitude periodic fluctuations in abundance in northern latitudes but exhibit damped cyclic dynamics in their respective southern ranges. Generalist predation and habitat loss have been identified as two features of southern habitats that may contribute to the attenuation of cycles in southern latitudes. I used a reaction-diffusion-advection framework to investigate the relative and combined damping impacts of generalist predation and habitat loss with reaction terms taken from the May and Rosenzweig-MacArthur models. The models were parameterized using data from snowshoe hare and Canada lynx field studies to generate similar cyclic dynamics in the center of a single patch in the absence of generalist predation. I found that generalist predation has strong stabilizing effects for both models and may represent a threat to the persistence of specialized predators. The magnitude of cycle damping due to habitat loss depends on movement rates and model choice, but ultimately results in the loss of cycles. Differences in model carrying capacity may explain differences in model sensitivity to habitat loss, and cycle amplitude may or may not decrease monotonically with habitat loss, depending on model choice. Elevated generalist predation rates at patch edges and in matrix habitat hasten cycle attenuation in situations that lead to increased prey exposure to generalists, including small patch size, higher movement rates into the matrix, and increased prey density at patch edges. Habitat disturbances may therefore have myriad consequences for cyclic systems depending in part on the nature of specialist predator-prey interactions and the extent to which the disturbances increase generalist access to prey. Field data that clarifies the relationships between habitat loss and fragmentation, generalist density and behavior, and cyclic activity would be invaluable in informing future modeling efforts.