DIFFERENTIATION OF THE SNAIL COMMUNITY ON THE NORTH-FACING AND SOUTH-FACING SLOPES OF LOWER NAHAL OREN (MOUNT-CARMEL, ISRAEL)

Comparisons were made between 14 macrogastropod species on the north-f acing slope (NF) and south-facing slope (SF) of Lower Nahal Oren, Moun t Carmel, Israel. Striking differences in habitat selection, as well a s interspecific and intraspecific differentiation, were found. The tot al numbers of sampled snails and shells were 7,304 and 2,125 for SF an d NF, respectively. Species diversity was lower on SF. Two zones were similar between slopes: the old alluvial river bank and the karstic zo ne. The alluvial zones on both slopes were dominated by Euchondrus, Xe ropicta, Monacha, and Helix engaddensis, albeit with different ratios, and a different species composition in the case of Euchondrus. Bulimi nus labrosus and Levantina caesareana were the typical inhabitants of the karstic zone in both slopes, but were accompanied by Sphincterochi la cariosa and Enchondrus saulcyi on SF, and by Pomatias olivieri, Pen e sidoniensis, and Eopolita protensa on NF. S. cariosa was the most ab undant species on SF, but was absent from NF. B. labrosus and L. caesa reana were more numerous on SF than on NF. SF-shells were significantl y smaller than the shells of the same species on NF. The prosobranch P . olivieri was dominant on NF but was also found in the more mesic pat ches on SF. Indexing the similarity between the zones within each slop e and between the slopes revealed that all four zones on NF clustered at a very small distance, followed by the clustering of the three rock y zones on SF. The alluvial zone on SF clustered to all the other zone s with a weak clustering value. However, each slope had a higher index of similarity than that for the whole community at the site.