Effects of spatial variation in food availability on spacing behaviour and demography of Eurasian red squirrels
In heterogeneous habitats with limited resources, spacing behaviour will affect individual variation in breeding success and density of populations, and is thus of general interest to ecologists. We investigated how red squirrels Sciurus vulgaris adapt their social organisation to fine-grained heterogeneity in habitat quality, studying spacing behaviour, habitat use and population dynamics in a forest in north Italy, characterised by a mosaic of high-quality (chestnut-pine) and poor-quality patches. We compared the data with those from more homogeneous broadleaf and mixed woodlands with similar overall tree seed abundance (“stable” habitats). Squirrels lived at lower densities (pre-breeding density 0.39–0.58 ha−1) than in “stable” habitats, although breeding rate was not reduced. Female breeding success was related to being primiparous as yearlings, and increased with body mass and proportion high-quality habitat in the home range. Persistency rate of females was as in stable habitats. It was higher than male persistency, but immigration and recruitment rates were male biased, resulting in even sex-ratio. All residents occupied high-quality patches, and no subadults established a permanent home range in poor-quality habitat. Home range and core-area size was typically larger in males than in females and a male's core-area overlapped those of other males and of females. Female core-areas were overlapped by males but not, or very little, by other females (intrasexual territoriality). Home ranges, or core-areas, were not smaller than in “stable” habitats, nor did we find a higher degree of core-area overlap. We conclude that in patchy habitats dominant, resident red squirrels exclude dispersing animals from preferred, high-quality habitat, producing a spacing pattern referred to as ideal despotic distribution, and that poor patches were only used temporarily by transient individuals, resulting in a reduction of density in comparison to populations in “stable” habitats.
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Document Type: Research Article
Publication date: October 1, 2001