Resting-site preference and patterns of spatial distribution were examined in the sympatric land snails Arianta arbustorum and A. chamaeleon on two opposite slopes in the south-eastern Alps, Austria. The two slopes did not differ in proportion of A. arbustorum and A. chamaeleon (74.4% vs. 25.6% on the NNE-exposed slope and 68.3% vs. 31.7% on the SSW-exposed slope). Individuals of both species showed aggregated dispersion patterns. The nearest-neighbour method indicated that in both species snail aggregations predominantly consisted either of A. arbustorum or A. chamaeleon on the NNE-exposed slope with a mosaic of rocks and distinct patches of different plants. On the SSW-exposed slope, which was less variable in vegetation cover, snail aggregations consisted of conspecific and hetero-specific individuals. Juvenile and adult A. arbustorum preferred to rest attached to leaves of Adenostyles alliariae, but avoided rock surfaces and patches of grass on the NNE-exposed slope. In contrast, juvenile and adult A. chamaeleon preferentially rested on rock surfaces, and also avoided grass patches. Juvenile and adult A. chamaeleon did not differ in resting-site preference, whereas small differences in resting sites were observed between juvenile and adult A. arbustorum. Differences in resting-site preference is one way of niche differentiation which may allow individuals of the two Arianta species to coexis
