Influence of Female Relatedness On the Demography of Townsends Vole Populations in Spring

1. The relatedness of individuals can influence their behaviour and changes in the degree of female relatedness in spring may influence the demography of vole populations (Lambin & Krebs 1991a). Here we report on an experiment testing the effect of relatedness on the demography of Townsend's vole (Microtus townsendii) populations (kin and non-kin treatments) over three consecutive springs. 2. Most nestlings were marked before weaning such that we knew which recruits were related to one another and to which adult female. The average size of matrilineal groups was experimentally manipulated by selectively removing voles of known origin and by preventing predation by birds of prey. 3. Nearest neighbours had their nests closer to one another on the kin treatment, but there were no differences in home range size between treatments. Home-ranges of females present on both treatments were smaller in a spring of high density than in the springs with lower density. 4. Female survival was better on the kin treatment. Within the kin treatment, females with at least one first degree relative as a neighbour survived better than females without such a relative. No such difference was observed within the non-kin treatment. 5. Females in the kin treatment gave birth to their first spring litter 5-7 days later than females in the non-kin treatment, possibly as a consequence of space sharing with related neighbours. The weaning success of the first spring litter was significantly higher on the kin tratment than on the non-kin treatment, but there were no differences in the weaning success of females with and without related neighbours within treatments. The presence of immigrant females on the non-kin treatment and not on the kin treatment may have caused the difference in weaning success between the treatments. 6. We conclude that female relatedness influences the pattern of space use and the survival of females in spring. The presence of immigrant females attempting to establish in the population has a pronounced effect on the weaning success of residents.