Diversities and distributions of 80 land-snail species in southeastern-most Madagascan rainforests, with a report that lowlands are richer than highlands in endemic and rare species

Replicated elevational transects (maximum range 100–860m) on three widely separated mountains yielded 2430 specimens sorted to 80 conservative morphospecies that were assigned to eight major groups. Species were classified as either rare (<0.5% of specimens) or non-rare. Endemic species, conservatively defined as non-rares that were collected on only one mountain and differed significantly in abundance among mountains (based on analysis of variance), comprised 13% of species and were found only at 100–400m. Four of the eight major groups had 80% of their rare species found at 100–400m, and the other four had no less than 50%. This lowland predominance of rares and endemics is unusual and unexpected, and needs to be confirmed by further studies.Previously it has been demonstrated that total land-snail diversity is significantly higher in the eastern, windward, coastal mountains (Vohimena Chain) than in the western, leeward, inland mountains (Anosy Chain). The present paper shows that this pattern holds (based on analysis of variance) for four of eight major taxonomic groupings of land snails (charopids, Microcystis, Kalidos, and non-Boucardicus prosobranchs), and does not exist for another four (Boucardicus, streptaxids, Sitala, and other pulmonates). Microcystis had by far the most rares and endemics (found on only one mountain), which represented 70% and 80% of its species, respectively. Boucardicus, the most diverse group (17 species), also showed the greatest variation in geographical and elevational ranges. Virtually no species of any group had an elevational range of less than 200m.These patterns imply that survey (sufficient at 200m intervals for snails) and conservation efforts should focus immediately on leaf-litter and soil invertebrates of Vohimena Chain forests, including strong emphasis on lowlands. The few remaining forest patches there are effectively unprotected and are undergoing rapid destruction by slash-and-burn agriculture.