Elements of the spatial organization of a common vole population

Abstract

Spatial parameters of a population of common voles Microtus arvalis (Pallas, 1779) in relation to colonies of burrows, were studied two years for two populations of these animals living in isolated fields of alfalfa each one hectare in extent. The CMR method was used. Trapping sites were set up in the centre of each colony. As the number of colonies increased their distribution changed from random to evenly spaced. In the population where density was high than this change took place almost a year earlier than in the low-density population. Individuals exhibited a tendency to distribution in groups. The number of colonies of burrows occupied by individuals increased asymptotically as population numbers increased. The increase in the number of colonies occupied by females is greater than those occupied by males. The average number of individuals in an occupied colony also increases (in a straight line) with increase in population numbers. It is chiefly the adult individuals which take part in the process of settling up new colonies and settling deserted burrows, and females do this to a greater extent than males. The majority of the individuals entering the population (about 90%) increase the density of already existing colonies. Spatial penetration of voles varies with the season and is higher at times of low population numbers than when these are high. Males were found to move over larger areas than females, and the same applies to older individuals as compared with young ones. The greatest differentiation in individuals from the aspect of spatial penetration was found during the year preceding the year of maximum population numbers.