Recruitment of a coral reef fish: roles of settlement, habitat, and postsettlement losses

Multiple processes typically influence patterns of abundance. Despite this widely accepted view, many studies continue to approach ecological questions from a single-factor, or, at most, a two-factor perspective. Here, I evaluate the consequences of considering, separately and jointly, the effects of three factors (larval settlement, reef resources, and postsettlement losses) on spatial patterns of abundance of a marine reef fish, the six bar wrasse (Thalassoma hardwicke). Using correlational methods commonly employed in single-factor studies, I show that local patterns of abundance of juvenile wrasse could be attributed entirely to either (1) patterns of abundance of settlement habitat, or (2) patterns of larval settlement. This result occurred because habitat and presumed larval delivery covaried in space. I manipulated abundance of settlement habitat in a field experiment to uncouple this covariation and found subsequent settlement to be simultaneously influenced by both factors. However, joint effects of habitat and settlement failed to account for patterns of abundance of juvenile wrasse without also considering a third factor - postsettlement losses - which were density-dependent and substantially modified patterns of settlement. These results illustrate (1) how multifactorial explanations may be falsely refuted when incomplete sets of multiple factors are considered, and (2) how single-factor explanations may misrepresent underlying multifactorial causation of ecological patterns. Uncovering the interactive role of multiple factors in determining ecological patterns of interest requires a shift from single-factor approaches to more pluralistic perspectives.