The significance of quantitative fluctuations in eurivalent land snails (Mollusca: Gastropoda Terrestria) in malacocoenoses

In this paper the quantitative fluctuations of seven taxa of land snails in the malacocoenoses of forest communities on the Medvednica mountain (north - western Croatia) are investigated. These taxa Aegopinella epipedostoma (FAGOT, 1879), Aegopis verticillus (FERUSSAC, 1822), Cochlodina laminata grossa (ROSSMASSLER, 1835), Perforatella incarnata (O. F. MULLER, 1774), Semilimax carinthiacus (WESTERLUND, 1886), Punctum pygmaeum (DRAPARNAUD, 1801) and Vitrea subrimata (REINHARDT, 1871) occur in all the malacocoenoses where research was conducted, and they are eurivalent in the Medvednica area within the context of forest phytocoenoses. Their absolute quantitative values were recorded - the densities of these taxa expressed by the number of specimens per unit volume, and the relative densities of taxa expressed as a percentage proportion of taxon in the malacocoenosis. The eurivalent species of snails have their maximum absolute densities in qualitatively and quantitatively rich malacocoenoses of basophilic, thermophilic phytocoenoses, and their minimum densities in qualitatively and quantitatively poor acidophilic phytocoenoses. The relative densities of the eurivalent species are greater in acidophilic phytocoenoses and least in thermophilic, basophilic phytocoenoses. Thus it was shown that a high absolute density of specific taxon does not have in consequence a correspondingly high percentage density, because the percentage density is the result of quantitative interrelationships between all the taxa in the malacocoenoses. The problem of utilising adequate methods to gather snail specimens is also considered