Density-dependence in habitat utilisation by wood mice in a Sitka spruce successional mosaic: the roles of immigration, emigration, and variation among local demographic parameters

Density dependence in habitat utilisation by a population of wood mice (Apo demus sylvaticus L.) was investigated within a habitat mosaic produced by t he felling of mature Sitka spruce (Picea sitchensis Bong. Carriere). A capt ure-mark-recapture study was carried out from May 1990 to June 1992, with t rapping in five 0.81-ha grids marked in mature forest and clear-fellings of different ages. Intergrid movements were frequent (15.3% of all recaptures ). A significant linear negative relationship was found between overall pop ulation sizes and degree of heterogeneity in habitat utilisation, although the former explained only about one-quarter of the variation in the latter (r(2) = 0.233). Wood mice were more evenly distributed among grids when num bers in the area were high, indicating density-dependence in their habitat utilisation. Demography was studied at subpopulation (grid) level to determ ine whether the observed pattern was due to movements among grids or to int ergrid Variation in the balance between recruitment and losses. Partial reg ression coefficients in a multiple regression showed that emigration/immigr ation had a lesser role in explaining the pattern, although the former was significant in explaining part of subpopulation decreases and the latter wa s significant in explaining part of their increases. Differences in the bal ance between recruitment and loss rates among local subpopulations accounte d for most of the observed density-dependent changes in habitat utilisation . These results do not support the view that such changes are mostly due to active choices made by individuals moving among habitats.