SURVIVAL AND LIFETIME REPRODUCTIVE SUCCESS IN DISPERSING AND RESIDENTRED SQUIRRELS

Dispersal in red squirrels (Sciurus vulgaris) is not sex-biased and st rict philopatry is rare. The immigration pattern suggests that nearly all animals have to disperse away from the natal site and that dispers al in this species is the outcome of local (intrasexual) competition. If this interpretation is correct, we predict that dispersers and resi dents, of both sexes, should have equal survival rates and lifetime re productive success. Body mass, longevity, reproductive success and dom inance rank of 34 resident offspring (settling within 400 m of the nat al range) and 70 immigrants (dispersers) were compared. Immigrants did not weigh less than residents as adults, nor did they have a higher m ortality during the pre-settling period. Survival rate, lifetime repro ductive success (females) and the proportion of males obtaining a high dominance rank were similar for residents and dispersers, and no sex effect was found on either of the parameters studied. These results ar e consistent with the hypothesis that local competition determines whe ther an individual disperses further away or settles close to its birt hplace.