“Seasonally varying predation behavior and climate shifts are predicted to affect predator-prey cycles”

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Rebecca Tyson and Frithjof Lutscher

Season-specific predator behavior, absent from current theory, may have dramatic effects on future ecosystem dynamics

Juvenile great horned owl (Bubo virginialis).
(Credit: Bob Lalonde)

Predator-prey interactions often lead to temporally oscillating population dynamics, most prominently documented in the snowshoe hare cycle in western Canada. While the theory of predator-prey interactions strictly distinguishes between specialist and generalist predators, the great horned owl, interestingly, is an example of a predator that switches its behavior seasonally: Its rate of killing snowshoe hare (functional response) in the Kluane region resembles that of a generalist in the summer and that of a specialist in the winter (Krebs et al. 2001). Since specialist predation is thought to enhance population oscillation and generalist predation to reduce it, researchers Rebecca Tyson (UBC Okanagan) and Frithjof Lutscher (University of Ottawa) asked how such a behavioral switch would affect population cycles.

Enter climate change and the prediction that winter season length decreases in high latitudes on average. How will the oscillating populations of owl and hare react when climate changes alters their interaction patterns? Will the existing cycles simply shift a little or could some more disastrous scenario ensue, such as extinction of either hares or owls?

The researchers carefully designed and analyzed a dynamical-systems model and used parameter values from the Kluane study to guide their investigation. For fixed season length, they find many more scenarios than simply stable or oscillating coexistence between predator and prey. For example, a predator whose behavior switches seasonally, with ample resources during the summer generalist phase can drive its winter specialist prey to extinction. Or initial conditions could determine whether the system reaches a steady state or an oscillating solution. When season length changes, the system can switch from one of these scenarios to another and back. Consequently, as global warming continues, the prey population cycle could potentially collapse, and predator and prey could stably coexist at much lower population densities. The loss of oscillations could have far-reaching consequences for the entire ecosystem. Read the Article

C. Krebs, S. Boutin, and R. Boonstra, eds. 2001. Ecosystem Dynamics of the Boreal Forest: The Kluane Project. Oxford University Press, Oxford and New York.