INTRINSIC DENSITY-DEPENDENT REGULATION OF VOLE POPULATIONS

CONSIDERABLE controversy exists over the role of density-dependent pro cesses in controlling animal population size. In populations that fluc tuate cyclically or erratically, for example many voles and insects1,2 , theory predicts that either density-dependence is weak1,3, or that d ensity-dependent responses lag behind density4-6. One key mechanism fo r lagged density-dependence is a delay in regeneration of food resourc es following heavy exploitation. Here we show that meadow vole (Microt us pennsylvanicus) populations respond immediately to high density by reducing breeding effort and hence population growth, disproving the h ypothesis that density-dependence is weak. In addition, vole populatio ns do not show a delay in growth following marked reduction in plant b iomass (their source of food and cover). We conclude that intrinsic de nsity-dependence processes tend to stabilize vole populations, and tha t cyclic dynamics are not caused by lagged effects of resource exploit ation.