Angels on the head of a pin: the occurrence and co-existence of clausiliid species in Europe

Abstract

While varying greatly in size, European clausiliids have a remarkably consistent and characteristic shell form that distinguishes them from all other land snails in the region. They are found in a wide range of habitats and are geographically widespread, occurring in boreal through to mediterranean climates. There are, however, regional differences in species richness and range sizes, and striking differences in the number of species that may be found syntopically, even in habitats that appear similar. Regions of high diversity do not always support many species co-occurring at site level. We explore these differences, using information on habitat and microhabitat differences between species to assess the extent to which co-occurrence might be limited by competition or environmental constraints. Neither provide a satisfactory explanation for all patterns, and the effects of Quaternary climate change and limited powers of dispersal are clearly important.