DIFFERENCES IN RESTING-SITE PREFERENCE IN TWO COEXISTING LAND SNAILS, ARIANTA ARBUSTORUM AND ARIANTA CHAMAELEON (HELICIDAE), ON ALPINE SLOPES

Resting-site preference and patterns of spatial distributionwere examined in the sympatric land snails Arianta arbustorumand A. chamaeleon on two opposite slopes in the south-easternAlps, Austria. The two slopes did not differ in proportion ofA. arbustorum and A. chamaeleon (74.4% vs. 25.6% on the NNE-exposedslope and 68.3% vs. 31.7% on the SSW-exposed slope). Individualsof both species showed aggregated dispersion patterns. The nearest-neighbourmethod indicated that in both species snail aggregations predominantlyconsisted either of A. arbustorum or A. chamaeleon on the NNE-exposedslope with a mosaic of rocks and distinct patches of differentplants. On the SSW-exposed slope, which was less variable invegetation cover, snail aggregations consisted of conspecificand hetero-specific individuals. Juvenile and adult A. arbustorumpreferred to rest attached to leaves of Adenostyles alliariae,but avoided rock surfaces and patches of grass on the NNE-exposedslope. In contrast, juvenile and adult A. chamaeleon preferentiallyrested on rock surfaces, and also avoided grass patches. Juvenileand adult A. chamaeleon did not differ in resting-site preference,whereas small differences in resting sites were observed betweenjuvenile and adult A. arbustorum. Differences in resting-sitepreference is one way of niche differentiation which may allowindividuals of the two Arianta species to coexist. (Received 14 March 1996; accepted 8 July 1996)