Forest snail faunas from Georgian Transcaucasia: patterns of diversity in a Pleistocene refugium

Thirty forest sites in Georgia were sampled to obtain inventories of their land snail faunas. The sites, in nine sampling areas, ranged from Batumi near the Turkish border to Lagodekhi near the Azerbaijan border, and included parts of both the Lesser and Greater Caucasus mountains and the Colchic lowlands. Abundance was generally low, and most sites held less than 20 species. Ninety species were found overall. Although sites within some sampling areas had very similar faunas, the overall levels of similarity among sites and sampling areas was low, especially when compared with similar forests from northern central Europe. Both climate and geographical position affected similarity: although these were correlated, independent effects of each were detected, and the effect of position alone was strongest. Despite this effect, most species have ranges extending into Turkey or Ciscaucasia, a few have very limited ranges, and there is no evidence of patterns of allopatric replacement among congeners. These patterns resemble those seen in faunas from forests in lower latitudes, and suggest a slow build-up of regional diversity by differentiation in situ, without the repeated restrictions to a multiplicity of small refugia that are characteristic of areas where fluctuations in aridity are important. The refugium has remained isolated, and has contributed little to the Holocene recolonization of areas further north. (C) 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102, 239-250.