SIZE, DOMINANCE AND COPULATORY SUCCESS IN MALE NORTHERN ELEPHANT SEALS, MIROUNGA-ANGUSTIROSTRIS

The relationship between size, dominance and copulatory success was in vestigated in male northern elephant seals to determine the importance of size in male intra-sexual competition for mates. The study was con ducted over four breeding seasons at the Ano Nuevo rookery in central California. Mass was estimated using a photogrammetrical technique in three seasons and measured directly in one. Copulatory success was pos itively correlated with size (mass and length). This correlation was m ediated through the positive effect of size on dominance rank; variati on in arrival mass, for example, accounted for 29-44% of the variation in dominance. Copulatory success was positively correlated with domin ance rank for mid- to high-ranking males, but not for low-ranking male s, which obtained few copulations. Copulatory success was not signific antly correlated with size when the effect of dominance was removed st atistically. These results support the hypothesis that male reproducti ve success in this species is principally determined by dominance rank , which, in turn, is affected by male size. However, they also suggest that large size is just one of a number of important factors that aff ect the outcome of male intra-sexual competition and hence, reproducti ve success.