Variation in spatial structure and abundance of Clausillids (Mollusca: Clausiliidae) in the nature reserve Debno Nad Warta (W. Poland) during wintering

Studies on the distribution and abundance of Cochlodina laminata, Ruthenica filograna and Clausilia bidentata in wintering conditions were based on a network of four permanent monitoring plots. Of the three clausiliids present, C. laminata was the most widely distributed, while the occurrence of R. filograna was limited to one plot. The small distribution area of the snail was compensated for by its high abundance. The distribution of clausiliids was found to depend signficantly on the soil humidity and temperature, these factors were, however, dependent on the litter composition which much better explains the observed variation. Canonical analysis (CCA) showed that R. filograna and C. bidentata preferred places with a sparse herb layer and a considerable proportion of litter of hornbeam (Carpinus betulus) and ash (Fraxinus excelsior). C. laminata was more tolerant with respect to the herb layer proportion, and the optimum of its occurrence was associated with alder litter (Alnus glutinosa). All three clausiliid species avoided litter of oak (Quercus), sycamore (Acer pseudo-platanus) and aspen (Populus tremula).