MODELING THE POPULATION-DYNAMICS OF ANNUAL PLANTS WITH SEED BANK AND DENSITY-DEPENDENT EFFECTS

A model is proposed for the population dynamics of an annual plant (Se sbania vesicaria) with a seed bank (i.e. in which a proportion of seed s remain dormant for at least one year). A simple linear matrix model is deduced from the life cycle graph. The dominant eigenvalue of the p rojection matrix is estimated from demographic parameters derived from field studies. The estimated values for population growth rate (lambd a) indicates that the study population should be experiencing a rapid exponential increase, but this was not the case in our population. The addition of density dependent effects on seedling survivorship and ad ult fecundity, effects for which field studies provide evidence, consi derably improves our model. Depending on the demographic parameters, t he model leads to stable equilibrium, oscillations, or chaos. Study of the behaviour of this model in the parameter space shows that the exi stence of a seed bank allows higher among-year variation of adult fecu ndity, without leaving the region of demographic stability. Field data obtained over 3 years confirm this prediction.