LAUSR

Ecological and historical factors influence the probability that a known invader will experience success in new locations. Using field and laboratory studies, we investigated how residence time and natural enemies (co-evolved castrating parasite, and native crabs) differ between two introduced populations of the intertidal snail, Batillaria attramentaria. The populations have substantially different invasion histories (~ 10 vs. > 80 years) and exhibit markedly different densities and tidal distributions. The less-dense, vertically-restricted population was recently introduced, and thus has potentially had less opportunity to fill the fundamental niche at that site. However, no increase in density or intertidal range occurred in this population over 10 years, suggesting that it had reached its realized niche. The newer population experienced much greater effects of native cancrid crabs than the older, high-density population, particularly below the minimum tidal elevation of observed snail distribution, where crabs were found in the greatest densities. Prevalence of parasite infection did not differ between populations. This is the first study documenting effects of predators on this invasive snail, which is widespread along coastlines of the northeast Pacific, whereas previous studies have suggested that the primary restriction on population growth rate was likely to be parasitic castration. Further, this study supports the general understanding that, while novel predators can reduce the impacts or population growth rates of invasive species, such top-down effects are not likely to preclude persistence at a given site.