Living on the edge: Space use of Eurasian red squirrels in marginal high-elevation habitat.

In marginal habitats located at the edge of a species’ range, environmental conditions are frequently
extreme and individuals may be subject to different selective pressures compared to central populations.
These so-called edge or marginal populations tend to have lower densities and reproductive rates than
populations located in more suitable habitats, but little is known about local adaptations in spacing
behavior. We studied space use and social organization in a population of Eurasian red squirrels (Sciurus
vulgaris) in a high-elevation marginal habitat of dwarf mountain pine (Pinus mugo) and compared it with
spacing patterns in high-quality Scots pine (Pinus sylvestris) forest at lower-elevation. Home ranges and
core areas were larger in the marginal habitat. In both habitats, males used larger home ranges than
females, but sex differences in core area size were significant only in the edge population. Patterns of
core area overlap were similar in both habitats with intra-sexual territoriality among adult females and
higher degrees of inter-sexual overlap, typical for the species throughout its range. However, low
densities in the edge population resulted in higher female by males overlap in spring-summer, suggesting
males increased home ranges and core areas during mating season to augment access to estrus
females. Thus, in the marginal habitat, with low food abundance and low population densities, linked
with extreme winter conditions, squirrels, especially males, used large home ranges. Finally, squirrels
responded more strongly to variation in food availability (inverse relation between home range size and
seed abundance), and even to fluctuations in density (inverse relation between core area size and density
of animals of the same sex), in the marginal than in the high-quality habitat, suggesting high behavioral
plasticity to respond to the ecological constraints in marginal habitats.