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

ABSTRACT

Comparisons were made between 14 macrogastropod species on the north-facing slope (NF) and south-facing slope (SF) of Lower Nahal Oren, Mount Carmel, Israel. Striking differences in habitat selection, as well as interspecific and intraspecific differentiation, were found. The total numbers of sampled snails and shells were 7,304 and 2,125 for SF and NF, respectively. Species diversity was lower on SF. Two zones were similar between slopes: the old alluvial river bank and the karstic zone. The alluvial zones on both slopes were dominated by Euchondrus, Xeropicta, Monacha, and Helix engaddensis, albeit with different ratios, and a different species composition in the case of Euchondrus. Buliminus labrosus and Levantina caesareana were the typical inhabitants of the karstic zone in both slopes, but were accompanied by Sphincterochila cariosa and Euchondrus saulcyi on SF, and by Pomatias Olivieri, Pene sidoniensis, and Eopolita protensa on NF. S. cariosa was the most abundant species on SF, but was absent from NF. B. labrosus and L. caesareana were more numerous on SF than on NF. SF—shells were significantly 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 patches on SF. Indexing the similarity between the zones within each slope and between the slopes revealed that all four zones on NF clustered at a very small distance, followed by the clustering of the three rocky zones on SF. The alluvial zone on SF clustered to all the other zones with a weak clustering value. However, each slope had a higher index of similarity than that for the whole community at the site.