Cyclic Mortality

Abstract

A speculative review of the factors causing cyclic mortality, the importance of intrinsic factors involving competition being stressed, while extrinsic, including climatic, factors are thought unimportant. The decline of birds and mammals which prey on cyclic rodents is attributed to the decline in the rodents; the decline of the rodents to their overeating their vegetable food; the decline of the gallinaceous birds to their being preyed upon by the predators of the rodents after the rodents have declined. The regularity of cycles is attributed to a basic predator-prey oscillation between rodents and their vegetable food which is little disturbed by other factors. Emigration helps to keep adjacent regions in step.