There is considerable debate regarding the major processes that determine population sizes of organisms inhabiting rocky and coral reefs. Most of these organisms have complex life cycles that include widely dispersive propagules and relatively sedentary juveniles and adults, such that the `birth rate` at a particular reef is equivalent to the rate of settlement of propagules. The controversy focuses on the extent to which supply of propagules vs. post-settlement processes determine local population size and dynamics. To resolve this issue we must know whether, and how, the demographic rates that determine population size at a particular site (settlement, immigration, mortality, and emigration) change with population density (i.e., are the changes in these rates density-dependent). Answering this question is of more than academic interest because, first, it provides the basis for understanding how local population size is regulated naturally, which is essential for effective management of fisheries and other natural populations, and second, it has seldom been answered adequately for any organism. This collaborative research is designed to answer the question of what drives local population dynamics in a comprehensive manner for four species of marine fish inhabiting two very different environments: temperate and tropical reefs. This multi-species, multi-system approach will provide some generality which can perhaps be applied to other marine systems, including demersal and bottom fisheries. Using well-proven methods, the combined experimental and observational design of this study will examine the roles of larval supply, settlement, recruitment, immigration, emigration, competition, and especially predation and its mechanisms, in driving local population dynamics. Results of the field work will be incorporated into mathematical models of population dynamics to provide conceptual generality applicable to other similarly organized systems.
