The distribution and population regulation of the wood mouse Apodemus sylvaticus on field boundaries of pastoral farmland.
The population characteristics and distribution of wood mice (Apodemus sylvaticus) were investigated along field margins of farmland in Northern Ireland, UK, dominated by grass production. Turnover, sex ratio, breeding season, spatial density dependence and density dependence in reproductive activity indicated that the population ecology of A. sylvaticus is consistent in different habitats in the same geographical region. Spatial variation in the abundance of A. sylvaticus was related negatively to percentage of land under pasture and distance from woodland and positively related to variables associated with food supply and cover. Variation in numbers of overwintered mice at the start of the breeding season was related more closely to breeding opportunity than to environmental factors. This was particularly so in males. The association of overwintered male and female A. sylvaticus remained evident in the latter half of the breeding season. Young males and females of the year, however, were distributed more with respect to physical and biological features than towards adults or reproductive opportunity. A. sylvaticus is an important species of field margins, even where these are poorly developed and agriculture is pastoral rather than arable. Further studies of this species in a wider range of agricultural systems are desirable.