The significance of variable and density-independent post-recruitment mortality in local populations of reef fishes

Abstract In this paper I focus on how post-settlement mortality may modify initial patterns of settlement in reef fish. Infrequent recruitment surveys may underestimate the role of early post-settlement mortality as most mortality in reef fishes occurs shortly after settlement. Consequently, results from infrequent recruitment surveys shed little light on the mechanisms producing patterns of abundance because these surveys ignore early post-settlement mortality. Variation in density-independent mortality may be a common mechanism that can prevent a positive relationship between larval settlement and subsequent population abundance. Although density-dependent mortality is the most commonly recognized mechanism that can disrupt the correlation between settlement and adult abundance, density-independent mortality’ can also destroy this correlation if the variance associated with post-settlement mortality is greater than variance in settlement. This point is illustrated with a simulation model in which I modelled two populations: a piscivorous fish population that was recruitment-limited with constant mortality, and a prey population that had variable recruitment and mortality that was a function of the size of the predator population. The results of this model indicate that even when mortality of prey is density-independent, predation can determine prey abundance when variation in piscivore recruitment is high relative to prey recruitment. Thus, initial patterns of prey settlement can be modified by a recruitment-limited predator population.