SPATIAL DYNAMICS OF A PATCHILY DISTRIBUTED BUTTERFLY SPECIES

1. Nine metapopulations of the butterfly Plebejus argus were mapped in North Wales in 1983 and 1990. The metapopulations occurred in three biotopes; five were in heathland, one in mossland and three in limestone grassland. 2. Within metapopulations, local distributions of the butterfly corresponded to the spatial distributions of suitable habitat: P. argus was able to colonize virtually all suitable habitat patches that were less than 1 km from existing, populated patches. 3. In contrast, the regional distribution was constrained by the inability of the butterfly to colonize suitable habitat that was further than a few kilometres from existing metapopulations; some of these sites are now populated by P. argus following successful introductions. 4. Turnover (extinctions and colonizations) of patches within metapopulations was relatively high in small patches. Turnover was also greater in heathland than in limestone: the principal reason for this was that patches of habitat were usually smaller in heathland, and small patches had high turnover in both biotopes. 5. Some patches changed in shape and size. Turnover of area was greater in heathland, where the butterfly occupies relatively transient successional habitats, than in limestone grassland where the habitat can be maintained in a suitable condition for longer periods. 6. The persistence of this spatially dynamic species depends on some suitable habitat being continuously available within relatively large areas of biotope. If the continuity is broken and a whole metapopulation becomes extinct, natural recolonization is unlikely to occur if the nearest P. argus source is more than a few kilometres away.