| Yhteenveto: | The role of intraspecific interactions - e.g. competition and kin interactions – in the regulation of vole populations has recently been under intensive scientific debate. The aim of this thesis was to study space use and reproductive success in relation to each other and quantity and quality of interacting individuals in the field vole Microtus agrestis. The methods used were intensive live trapping of natural populations, follow up of individuals of known relatedness in large outdoor enclosures and experimental manipulation of familiarity and relatedness in enclosed populations. The study of natural populations revealed that space use of breeding voles varied between sexes, among age classes and habitats, in time and with population density. Home range overlap between breeding females increased with increasing population density. Among females studied in the enclosures number of breeding sons and number of weaned young correlated positively with the distance to the nearest breeding female. Age, survival and bodyweight were other factors related to reproductive success. Females that lived with close kin seemed to be more successful at weaning young than those that lived separately. Weaning success of nonphilopatric young females correlated positively with distance to the nearest unrelated older female whereas that of philopatric young females did not. Mothers and their philopatric breeding daughters lived closer to each other than other breeding females. Philopatry of young maturing females was common only in the early part of the study. Later on kin clusters were rare. This result contradicts somewhat with the general assumption of philopatry among young female voles. Experimental manipulation of familiarity did not have any remarkable effects on space use and reproductive success of breeding field vole females. I conclude that the flexible space use of breeding female field voles seems to be a means to adapt to prevailing conditions. However, the way the space use react on density and relatedness between breeding females makes it incapable to regulate breeding density.
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