Refugial occurrence and ecology of the land snail Vertigo lilljeborgi in fen habitats in temperate mainland Europe
Vertigo lilljeborgi (Westerlund, 1871) is one of the rarest terrestrial snail species in temperate mainland Europe, traditionally considered a glacial relict there. This contrasts with its occurrence in northern Europe where it is a widespread species. This species prefers constantly wet habitats that are neutral to slightly acidic, and avoids highly alkaline conditions, which is an extremely rare ecology for a Eurasian mollusc. Until 2012, only five historical records of this species were known in mainland Europe to the south of its main distribution in northern Europe. Since then, 20 new sites have been discovered, mostly located in the Hercynian Mountains (Bohemian Massif in the Czech Republic and Massif Central in France). In comparison with the boreal European and Alpine populations, those from the Hercynian Mountains inhabit acidic, rather soligenous and productive fens, strongly dominated by Sphagnum. Vertigo lilljeborgi does not occur in some sites with apparently suitable habitats as indicated by species composition of the vegetation. We observed a surprising correspondence between the occurrence of V. lilljeborgi and mean July air temperature and we report its first fossil record from the last glacial period from Central Europe. Although the number of its sites has increased recently, these sites represent unusual and highly unique habitats, vulnerable to drainage and destruction from human activities. This calls for a need of conservation efforts in most of the newly discovered isolated sites.