Bank vole biology: recent advances in the population biology of a model species

Abstract

The results of studies on demography of an island population of Clethrionomys glareolus are presented. Population numbers and structure were estimated 5 times a year in 1966-1999. Two patterns of seasonal changes in population size were found: either continuous, slow increase from April (beginning of the breeding season) to October, with maximum density below 50 individuals per hectare, or rapid increase resulting in a July/September peak with maximum density up to 153 individuals per ha. The highest variations in numbers occurred in April (Whittaker's CF=2.05) and decreased with advancement of the breeding season: in September CF=1.49. The mechanism accounting for the decrease was territoriality of mature females. Fluctuating July population numbers revealed cyclic changes, namely a 3.8-year as well as a 9.4-year cycle. It is postulated that social relations between neighboring individuals rather than mean population density affect changes in population numbers.