AN EMPIRICALLY BASED MODEL FOR LATITUDINAL GRADIENT IN VOLE POPULATION-DYNAMICS

Vole dynamics in northern Europe exhibit a well-defined geographical g radient, with oscillatory populations being confined to high latitudes . It has been proposed that oscillations in northern vole populations are driven by their interaction with specialist predators (weasels), w hile the more southern rodent populations are relatively stable becaus e of regulation by generalist predators. We tested this generalist/spe cialist predation hypothesis by constructing an empirically based mode l for vole population dynamics, estimating its parameters, and makng p redictions about the quantitative pattern of the latitudinal shift in vole dynamics. Our results indicated that the model accurately predict ed the latitudinal shift in the amplitude and periodicity of populatio n fluctuations. Moreover, the model predicted that vole dynamics shoul d shift from stable to chaotic as latitude is increased, a result in a greement with nonlinear time-series analysis of the data. The striking success of the model at predicting the shifts in amplitude and stabil ity along the geographical gradient in northern Europe provides strong support for the key role of specialist and generalist predators in vo le population dynamics.