Variation in metapopulations of the polymorphic land snail Cepaea nemoralis (L.) in two small towns beyond its natural range

Variation in the shell colour and banding polymorphism in populations of the land snail Cepaea nemoralis was studied in the towns of Skara (central Sweden), and Kudowa Zdrój (south-west Poland), both recently colonised by the species. In both towns, populations were highly polymorphic; populations in each did not differ from each other as much as in cities recently invaded. Population density was higher in Kudowa, and its populations were both marginally more polymorphic and differed less among each other than at Skara. A single introduction followed by local spread seems the simplest explanation of the patterns observed. There was no evident geographical pattern in either case, suggesting that leptokurtic, passive dispersal plays a role, even at a local scale.