Ecological and historical determinants of Western Carpathian populations of Pupilla alpicola (Charpentier, 1837) in relation to its present range and conservation

The minute snail Pupilla alpicola (Stylommatophora: Pupillidae) is known as a threatened glacial relict restricted to treeless calcareous fens with Holocene continuity, mainly in the Alpine and Carpathian regions. We summarize all available data on the distribution of P. alpicola and analyse its ecological requirements in the Western Carpathians both at a larger, regional scale (162 sites) and at a smaller, within-site scale (10 sites). Viable populations of Pupilla alpicola occurred in 31 sites out of the 162 fens studied. Water conductivity, Ellenberg’s indicator values for soil reaction, light and nutrients were the main ecological variables that explained these occurrences. The species preferred sites with extremely high calcium carbonate precipitation, low nutrients and sparse herb vegetation cover. Its present distribution in the Western Carpathians is strongly related to a spatial–temporal continuum of calcareous fens throughout the Holocene; none of the modern populations was located further than 40 km from the known palaeorefugium. Direct fossil evidence shows that these palaeorefugial fens have persisted since the Pleistocene/Holocene transition. A conservation strategy for this rare species needs to take account of both historical continuity and the maintenance of appropriate ecological conditions.