Influence of Daylength on Activity of the Varying Lemming

Abstract

The importance of lemmings in the arctic and subarctic regions has long been recognized, but there is little known about their ecology. The cause of cyclic populations in these animals remains unknown. In all of the studies so far recorded, the die-off has been in the winter or early spring following a population peak. At this time (in late winter) the length of daylight begins to increase, and it has been postulated that the increased light stimulates most mammals into sexual activity (Christian, 1950). This has not been demonstrated in the varying lemming, and furthermore, these animals are reproductively active at all periods of the year (Degerbol and Mohl-Hansen, 1943; Manning, 1954; Ross, 1835; Sutton and Hamilton, 1932). Elton (1942) indicated that intraspecific factors may be the primary causes of population fluctuations. Errington (1946) included “fighting” as one of the intraspecific mechanisms which he believed basically determined population levels. Chitty (1952) puts forth the hypothesis that fighting produces physiological changes in parents which give rise to abnormalities in the young. Clark (1953) showed the effects of fighting on the adrenals, thymus and spleen of the vole Microtus agrestis , and stated that it produced a “weakened” condition in voles. Since fighting is a part (or result) of activity, it was deemed desirable to study the activity of varying lemmings, Dicrostonyx groenlandicus rubricatus (Richardson), in relation to increased daylengths. Moreover, most intraspecific interactions are the result of activity and/or activity patterns. Methods and materials .—A litter of varying lemmings was collected at Umiat, Alaska, and transported to Fort Collins, Colorado. They survived to breed and establish a laboratory colony, on which this study is based. Four animals (2 males, 2 females) were housed in separate cages. Each cage was approximately 23.5 cm. wide by 28.5 cm. long …