Relative importance of recruitment and other causes of variation in rocky intertidal community structure

Abstract

Recruitment limitation has been advocated as a major cause of community structure on rocky shores. Earlier work was criticized for failing to assess this possible source of variation. To evaluate this suggestion in relation to factors already known to be important in such communities, I incorporated estimates of recruitment with data from prior experiments in New England and Panama and reanalyzed the results using multiple regression. Rates of increase of prey abundance in predator exclusion experiments in New England were at least an order of magnitude greater than in Panama (e.g., ti took 4–6 mth vs. 60–72 mth to reach 100% cover, respectively). Recruitment densities of sessile invertebrates and algae were variable in space and time at both sites, but were lower by at least an order of magnitude and less synchronous in Panama than in New England. The analyses indicated that, although predation, competition, recruitment, and level on the shore explained significant amounts of variation in community structure at both places, the proportionate contributions of these factors differed. In New England, recruitment explained at most 11% while predation and competition explained 50% to 78% of variation in sessile invertebrate abundance. In Panama, recruitment explained 39% to 87% while predation and competition explained 8 to 10% of variation in sessile invertebrate adundance. Hence, when low, recruitment density appears important in influencing the structure of these communities.