Fluctuating asymmetry and body size as indicators of stress in red squirrel populations in woodland fragments.
Abstract
In large parts of Europe red squirrels (Sciurus vulgaris) live in fragmented woodlands where populations are small, and dispersal rate and genetic diversity are reduced. These populations are, therefore, more likely to have been exposed to substantial environmental and/or genetic stress. Fluctuating asymmetry (FA) represents a measure of the sensitivity of development to stress. The expression FA was examined from November 1990 to November 1993 in the hind foot of live squirrels caught from 2 large (continuous) woodland sites (300 and 600 ha) and 6 small woodland fragments (17-55 ha) in north Belgium, for which data were available on squirrel population density, reproductive rate and genetic variation. Squirrels in small woodland fragments were smaller and had a slightly higher degree of FA than squirrels from large woodland sites. In the fragments, heavier squirrels tended to have a lower degree of FA, and reproducing females were less asymmetric than non-reproducing females, indicating that in small populations FA increased in poor quality individuals. Inter-population variation in the mean level of FA could not however be correlated with genetic similarity, or with woodland quality as measured by the sum of the proportion of pine (Pinus sylvestris, P. nigra) and oak/beech (Quercus robur, Q. rubra/Fagus sylvatica) stands (all important food producing trees for squirrels) at the sites.