How Spatial Heterogeneity Influences Population Dynamics: Simulations in SEALAB

The influence of nest site selection on population dynamics is explored by considering two reproductive strategies. The first one, described as opportunist, is the most common in ecology. It postulates that an individual tries to select and track the optimal environmental conditions that maximize its total reproductive output. The second one, described as obstinate, comes from a generalization of "natal homing" recently proposed by Cury (1994). It assumes that a newborn individual memorizes early environmental cues that later determine its reproductive environment. We use an individual-based model named SEALAB to track artificial fish in a heterogeneous environment displayed as a lattice of hexagonal patches. The effects of two components of the lattice structure—namely the composition (amount of each patch type) and the configuration (spatial arrangement of patches)—on the success of the searching behavior are examined. For the obstinate strategy, whose searching behavior is characterized by a simple random walk, a spatial redundancy index seems sufficient to account for the spatial heterogeneity influence, whereas for the opportunist strategy, more subtle indices are needed. We develop a quantitative measure of spatial local optima that could apply to any searching behavior based on local hill-climbing or local gradient information. Our results indicate how heterogeneity causes opportunist individuals to get stuck in local spatial optima. The use of a spatially explicit individual-based model such as SEALAB is justified by the possibility of carefully estimating simultaneously the value and the sensitivity of global parameters in relation to the spatial heterogeneity of the environment.