Evidence That Metapopulation Dynamics Maintain a Species' Range Limit

The metapopulation hypothesis for range limits proposes that geographic variation in a species' extinction from and/or colonisation of habitat can generate an abrupt range limit. We tested whether this contributes to the northern range limit of coastal dune plant Camissoniopsis cheiranthifolia by quantifying suitable habitat area and the rates of extinction and colonisation across 3485 plots throughout the northern half of the species' range. Colonisation of previously unoccupied plots increased with suitable habitat area and abundance in nearby plots and consequently declined towards the range limit. Extinction was more frequent from plots with less habitat and lower initial abundance but did not increase significantly towards the limit. Incorporating spatial variation in estimated rates of colonisation and extinction in a metapopulation model predicted a decline in plot occupancy towards the limit that closely matched the observed decline in occupancy. Thus, variation in metapopulation dynamics may contribute to this species' range limit.