Chapter 14 - Density Dependence in Reef Fish Populations

Abstract

This chapter suggests two major patterns related to the density dependence in coral reef fish population. Demographic density dependence is generally defined as an effect of the present and/or past population sizes on the per-capita population growth rate. Coral reef fishes support major fisheries and are the object of conservation efforts in their own right. They are ideal subjects for both observational and experimental population studies. The total local recruitment rate varies in a broad variety of patterns as a function of local population size. Although recruitment is not a consistent source of demographic density dependence in every study, conversion from total to per-capita recruitment results in apparent or pseudo-density dependence, which can provide a nonmechanistic kind of local population equilibrium unrelated to the regulation of the entire metapopulation. The data on 20 species from six families shows that postsettlement mortality is often density-dependent, especially shortly after settlement, which is caused largely by predation. Overall, 17 of 20 species experienced density-dependent per-capita mortality at some time and place. In most studies that reported density-independent mortality, the study of older juvenile fishes suggested that regulation via mortality is an early postsettlement phenomenon. The prevalence of density-dependent mortality has two effects. First, local populations may be an important source of regulation for the entire metapopulation, suggesting the importance of conserving the mechanisms causing local density dependence. Second, the more restrictive version of the recruitment limitation hypothesis that predicts that postsettlement mortality may be density-independent has been falsified in most cases.