CORRELATED EXTINCTIONS, COLONIZATIONS AND POPULATION FLUCTUATIONS IN A HIGHLY CONNECTED RINGLET BUTTERFLY METAPOPULATION

The persistence of metapopulations is likely to be highly dependent on whether population dynamics are correlated among habitat patches as a result of migration between patches and spatially-correlated environm ental stochasticity (weather effects). We examined whether population dynamics of the ringlet butterfly, Aphantopus hyperantus, were synchro nous in an area of approximately 0.5 km(2), with respect to extinction , colonization and population fluctuations. Monks Wood Butterfly Monit oring Scheme transect count data from 1973 to 1995, revealed (A) a maj or environmental perturbation, the drought of 1976, which caused synch ronized extinctions of A. hyperantus in subsequent years, (B) synchron ized recolonization in years following the large number of apparent ex tinctions, and (C) population changes by A. hyperantus were highly cor related in many of the 14 sections of the transect, presumably re flee ting similar responses to environmental stochasticity, and the exchang e of individuals among sections. However, extinction and population sy nchrony depended on habitat type. Following the 1976 drought, A. hyper antus apparently became extinct from the most open and most shady habi tats it occupied, with some persistence in habitats of intermediate sh ading, thus showing retraction to core populations in central parts of an environmental gradient, albeit with an average shift to relatively open habitat. Populations at extreme ends of the environmental gradie nt occupied by A. hyperantus fluctuated least synchronously, suggestin g a potential buffering effect of habitat heterogeneity, but this was not crucial to survival after the 1976 drought. Thus, not all habitats are equally important to persistence. Correlated temporal dynamics, v ariation in habitat quality and the interaction between habitat qualit y and temporal environmental stochasticity are important determinants of metapopulation persistence and should be incorporated in metapopula tion models.