A Dynamic Model of an Estuarine Invasion by a Non-Native Seagrass

Mathematical and simulation models provide an excellent tool for examining and predicting biological invasions in time and space; however, traditional models do not incorporate dynamic rates of population growth, which limits their realism. We developed a spatially explicit simulation model that allows patch or population growth rate to change with population size through the incorporation of field data. We used the model to evaluate the invasion of a west coast estuary by the non-indigenous Japanese eelgrass, Zostera japonica (Zosteraceae). Specifically, we tested the relative importance of stochastic, abiotic disturbance, interspecific competition, and vegetative and seedling survival. Our model predicted that vegetative shoot and seedling survival limited by competition are the most important limiting factors for Z. japonica growth, although stochastic disturbance was also a limiting factor. Population cycles and patchy distribution were also predicted, with the eelgrass apparently coexisting with the competitor. The model should be applicable to a variety of invasive species, with various types of disturbance and limiting factors.