LIFETIME REPRODUCTIVE SUCCESS AND ITS CORRELATES IN FEMALE EURASIAN RED SQUIRRELS

Individual variation in lifetime reproductive success (number of weaned offspring in a lifetime) of female red squirrels was studied in two populations in North Belgium for 8 yr. Fitness, the number of reproducing offspring, was calculated combining expected survival to reproductive age of dispersing young and reproductive performance of local recruits. Of 66 resident females, 20 (30%) never produced young. 89% of territorial females had offspring, while all non-territorial females failed to reproduce. Lifetime reproductive success of mothers (females that produced at least one weaned young) averaged 5.04 young (range 1-11), fitness averaged 2.07 (range 0.26-4.44). Both measures of reproductive success were strongly correlated (R(2) = 0.73). Variation in fitness and lifetime reproductive success was mainly the consequence of variation in the number of litters produced. Variation in body condition, foot length (size) and territory quality explained 50% of variation in the number of litters. Variation in the number of young/litter, age at first breeding and year of birth were not significantly correlated with variation in lifetime reproductive success. We conclude that large, heavy females that established home ranges in food-rich areas live longer and produce more young than lighter, shorter-lived females living in poorer territories, and discuss the occurrence of chance-events affecting reproductive output in young and old squirrels.