Crossing to safety: Dispersal, colonization and mate choice in evolutionarily distinct populations of Steller sea lions, Eumetopias jubatus.

Population growth typically involves range expansion and establishment of new breeding sites, while the opposite occurs during declines. Although density-dependence is widely invoked in theoretical studies of emigration and colonization in expanding populations, few empirical studies have documented the mechanisms. Still fewer have documented the direction and mechanisms of individual transfer in declining populations. Here we screen large numbers of pups sampled on their natal rookeries for variation in mtDNA (n=1,106) and 16 microsatellite loci (n=588) and show that new Steller sea lion breeding sites did not follow the typical paradigm and were instead colonized by sea lions from both a declining (Endangered) population and an increasing population. Dispersing individuals colonized rookeries in the distributional hiatus between two evolutionarily distinct (st = 0.222, st = 0.053, K=2) metapopulations recently described as separate subspecies. Hardy-Weinberg, mixed-stock and relatedne...