Environmental fluctuations and asymmetrical dispersal: generalized stability theory for studying metapopulation persistence and marine protected areas

Dispersal of individuals among subpopulations is a key process underlying metapopulation dynamics. Many metapopulation models, including those of coastal benthic organisms under marine reserve scenarios, have assumed a particular and time-independent dispersal pattern. The behavior of such models, however, may be sensitive to more realistic representations of oceanic dispersal. We examine the importance of environmental variability and dispersal characters for metapopulation persistence using a space-limited metapopulation model, in which the dispersal phase is represented by a connectivity matrix and environmental fluctuations by stochastic perturbations of adult abundances. The model is suited to marine organisms, but the same principles apply to other systems. When dispersal is asymmetrical, as expected in the presence of a dominant current, environmental variability can allow the metapopulation to persist, even when the per capita larval production rate is too low to otherwise sustain the population. This suggests that metapopulations inhabiting finite ranges in an advective environment may be more susceptible to variations related to climate change. Generalized stability theory is a powerful tool for identifying the local populations that have greatest impact on the metapopulation, and hence the optimal sites for protection from exploitation. We show that the inclusion of realistic environmental variability and complex dispersal patterns in models of marine reserve networks can bring unsuspected and sometimes largely positive effects for conservation and management of benthic species. Thus, marine reserve monitoring of abundance and recruitment in systems with longshore currents should include the region of long-distance dispersal of the species.