Geographical variation in the composition and richness of forest snail faunas in northern Europe

WA Museum Records and Supplements | Updated 8 years ago

ABSTRACT – The forest snail fauna of northern Europe originated from postglacial colonization from the south. While it is regionally poor (c. 150 species, excluding slugs), individual localities (clusters of sample sites within a few km of each other) can be rich by global standards (up to 57 species). Distance decay in faunal similarity is very gradual in lowland regions, but Carpathian faunas are sharply differentiated, and hold the most endemics. British faunas are remarkably uniform. Very little of this differentiation is due to congeneric replacement; it results mostly from shifts in the richness of whole families. Clausiliids in particular predominate in the Carpathians and adjacent areas, but this is not reflected in the apparent density of individuals: as species richness increases, average abundance of each declines. In general, small species are more Widely distributed than large ones. Although the richest localities are found in the Carpathians, regional variation in local richness is slight. Substrate has Significant effects: oligotrophic areas have poorer and more locally variable faunas. At a slightly larger scale, areas of less than 100 km2 holding more than 60 species can be found in many parts of the region (even more when slugs are included); the richest such patches hold about half the whole regional forest fauna. Comparison with limited data from regions further south shows that although they have much richer regional faunas, local communities are no richer than those of the north. Distance decay is much more rapid. These results are discussed, with global comparisons, in terms of the ways in which molluscan communities are assembled and structured.