A Metapopulation Model for Primula Vulgaris, A Temperate Forest Understorey Herb

Abstract

1 We suggest that Primula vulgaris in woodland habitats may form metapopulations: colonization is associated with the opening of canopy gaps and local populations become extinct as the canopy closes. The metapopulation is seen as a permanently changing system in which colonizations and extinctions are constantly occurring, coupled with forest canopy dynamics. 2 To describe metapopulation dynamics we use a Markovian model that incorporates the different stages through which local populations pass; we calculate the transition probabilities among those stages and estimate colonization and extinction rates. We combine empirical information on the demography of local populations and the dynamics of the forest mosaic in the model and use it to explore the effect of seed dispersal, fd (i.e. the fraction of seeds dispersing out of populations) and forest disturbance rate, k, on metapopulation growth rate, XM (i.e. the rate at which the number of populations in the metapopulation increases or decreases). 3 Increasing either fd or k has a positive effect on the projected metapopulation growth rate: higher disturbance rates increase the frequency of newly opened gaps in the environment and higher seed dispersal levels increase the probability of gap colonization. 4 Metapopulation growth rate is also affected by a number of other variables. It declines when time to local population extinction decreases and when fecundity is lower. The latter emphasizes that sufficient seeds must be available for dispersal to ensure gap colonization. 5 Stable patch/population-type distributions given different parameter values were obtained as the right eigen-vectors of metapopulation matrices. The proportion of forest patches occupied by P. vulgaris populations at equilibrium would be expected to be negligible under low k andfd values. 6 Metapopulation structure may break down under high disturbance rates because P. vulgaris local populations may never go extinct and thus seed dispersal would not play a major role in local population re-establishment.