Distinguishing between modes of dispersal by introduced eastern grey squirrels, Sciurus carolinensis
I tested between the competing hypotheses that the current distributions of introduced eastern grey squirrels in Victoria and Vancouver, BC, reflect unassisted dispersal versus an additional effect of human-mediated dispersal. Dispersal has traditionally been modeled and analyzed by ecologists by assuming continuous, random spread over homogenous landscapes. Squirrel dispersal in Victoria and Vancouver has been discontinuous and non-random over heterogeneous landscapes. As an alternative to traditional methods of modeling dispersal, I used weighted surface analysis in Geographic Information Systems. I estimated squirrel habitat preference and rates of spread, and then classified the landscape into friction values that reflected presumed ease of movement. Dispersal across barriers or other high-friction areas were inferred to result from humanmediated dispersal. At both sites, the current grey squirrel distribution is best accounted for by the combination of unassisted and human-mediated dispersal.