From physiology to space use: energy reserves and androgenization explain home-range size variation in a woodland rodent.

This study tested the relationships between both individual-level and predation-risk factors and the size of two home-range regions (HRR), defined as areas of different intensities of use. We have expanded on previous home-range studies by testing the effects of two previously ignored individual-level factors: androgenization and energy reserves (body fat). Location data were collected for wild individuals of Apodemus sylvaticus using the novel method of implanted PIT tags and mobile recording stations. A total of 68 home ranges were estimated using kernel density estimation. Home ranges were split into two regions (HRR): the 'core', representing the most intensively used areas, and 'periphery' regions. Body mass, body fat, sex, anogenital distance (AGD) (a proxy for androgenization) and the proportion of HRR, covered by antipredatory features (shrubs and fallen trees), were tested for their relationship with the size of core and periphery HRRs. Models were constructed for each HRR for three seasons: nonbreeding season (NBS), early and late breeding seasons (LBSs), to account for seasonal variation in behaviour associated with changes in food abundance and reproductive cycles. Body fat had a negative relationship with periphery size and an interaction with sex on core size in the early breeding season (EBS). Body mass also had a significant interaction with sex on core size in the EBS. Androgenization has a strong effect on home range size in both sexes: AGD had a positive relationship with both HRRs for males in the LBS and females in the NBS. Males had larger peripheries than females in both early and LBSs. Habitat features that reduce predation risk explain HRR size throughout the breeding period. This study emphasizes the importance of embracing natural complexity to gain insight into the drivers of space use behaviour; the consideration of individual and ecological factors, the recognition of the species-specific selective pressures that seasonal change presents for each sex and the identification of biologically meaningful home range areas will help advance the field.