Spatially-explicit individual based modeling of marine populations: a review of the advances in the 1990s

The utility of individual based models (IBMs) is that properties of ecological systems can be derived by considering the properties of individuals constituting them. Individual differences may be physiological, behavioral or may arise from interactions among individuals. The differences result in unique life histories, which when considered as a whole give rise to growth and size distributions that provide a measure of the state of the population. Early IBMs generally did not consider the effect of a spatially variable physical environment. Recent advances in ocean circulation models that include realistic temporal and spatial variation of currents, turbulence, light, prey, etc., have enabled IBMs to be embedded in model flow fields and for unique, sometimes behaviorally modified, Lagrangian trajectories to be computed. The explicit consideration of realistic spatial heterogeneity provides an additional factor that contributes to the differentiation among individuals, to variances in population structure, and ultimately to our understanding of the recruitment process. This is particularly important in marine environments where fronts, boundary layers, pycnoelines, gyres and other smaller spatial features have been hypothesized to play a significant role in determining vital rates and population structure. In this paper we will review the status of research on spatially-explicit IBMs, their successes, limitations and future developments. Examples will be drawn from approaches used in the past decade in GLOBEC, FOCI, SABRE and other programs.