Abstract
Seton (1909) stimulated wide interest in the fluctuation of population density of Arctic mammals. However, his account of suicidal migrations of lemmings was based on legend, as were the accounts of periodic erruptions of house mice, rats and voles. Since then, many investigations have presented conflicting ideas on the causes of density cycles in small mammalian populations. | Cyclic variations of numbers in lemmings, voles and mice populations involve several common factors. These factors include ecological (Thompson, 1955; Pitelka, 1962) ethological, (Krebs, 1964a; Christian and Davis, 1964; Sadlier, 1965; Chitty, 1957), physiological (Christian, 1963b; Bronson and Eleftheriou, 1963a; Andrews, 1968a), reproductive (Kalela, 1962 ; Mullen, 1965; Chitty and Phipps, 1966), and mortality (Krebs, 1964; Sadlier, 1965; Chitty, 1960; Chitty and Phipps, 1966; Lidicker, 1965) studies. In general, the influence of these factors may be segregated into two classes: extrinsic factors and intrinsic factors.