Determinants of reproductive success in voles: space use in relation to food and litter size manipulation

Spacing behaviour of female mammals is suggested to depend on the distribution and abundance of food. In addition, food limitation has been found to constrain the reproductive success of females. However, whether females maximize their reproductive success by adjusting space use in relation to current food availability and reproductive effort (e.g. litter size) has not been experimentally studied. We examined these questions by manipulating simultaneously food resources (control vs. food supplementation) and litter sizes (control vs. plus two pups) of territorial female bank voles (Clethrionomys glareolus) in large outdoor enclosures. Females with supplementary food had smaller home ranges (foraging area) and home range overlaps than control females, whereas litter size manipulation had no effect on space use. In contrast, the size of territory (exclusive area) was not affected by food supplementation or litter size manipulation. As we have previously shown elsewhere, extra food increases the reproductive success of bank vole females in terms of size and proportion of weaned offspring. According to the present data, greater overlap of female home ranges had a negative effect on reproductive success of females, particularly on survival of offspring. We conclude that higher food availability increases the reproductive success of bank vole females, and this effect may be mediated through lower vulnerability of offspring to direct killing and/or detrimental effects from other females in the population. Moreover, it seems that when density of conspecifics is controlled for, home range sizes of females, but not territoriality, is related to food resources in Clethrionomys voles.