Regional dynamics and dispersal in the vascular plant Silene viscosa (L.) inhabiting small islands

We investigated and compared the patch occupancy and colonisation and extinction over a 40-yr period in the vascular plant Silene viscosa in two archipelagos off the Swedish east coast. We also assessed the importance of regional vs local dynamics for regional persistence by examining factors affecting colonisation and extinction processes. We found an effect of isolation on the patch occupancy in 1957, but this effect disappeared 1997. The effect of isolation was not detected when analysing colonisations and extinctions during the 40-yr period separately, which suggests that the colonisations and extinctions since 1957 have changed the patch occupancy of S. viscosa. The change in the patch occupancy is attributed to an increased colonisation, presumably mediated by the increase of the greylag goose Anser anser. The large amplitude of population size change, the high persistence of populations during a 40-yr period, and the long term persistence for some populations all suggest that the distribution pattern approximates a distribution that is expected to be generated from an Island-Mainland model, where a number of large populations are persistent and a number of smaller populations are more prone to extinction due to catastrophes (nesting cormorants) and environmental stochasticity (summer drought). Most evidence suggests that regional processes are of less importance than local processes for regional persistence on a time scale of 40 yr for S. viscosa.