Small scale factors affect population size of the wood mouse (Apodemus Sylvaticus) in a Mediterranean island (Sardinia)

The variation of population size of the Wood Mouse (Apodemus sylvaticus) was studied across 30 independent transects in Sardinia island (Italy), with emphasis on the relationships between population size and environmental variables (type of wood, litter depth, tree diversity, tree size, number of stumps, ground cover, shrub cover, dead wood). Studies were conducted through a capture-mark-recapture protocol with live traps placed along line transects, and surveyed in both spring and autumn. Seven environmental variables were contrasted to population size estimates in each transect, with estimates of population size being obtained from five distinct demography models for close populations. There were significant inter-seasonal differences in the number of captured specimens (peak in springtime), but the population size of the Wood Mouse, despite varying considerably by transect, did not differ significantly among types of forest habitats. Population size of this species was positively influenced by (i) ground cover, (ii) number of stumps, and (iii) % Erica arborea; conversely, it was negatively influenced by (a) height of Rubus uhnifolius bushes and (b) by % Rubus ulmifolius. The possible reasons behind these patterns were explored and discussed.