DIVERSITIES AND DISTRIBUTIONS OF 80 LAND-SNAIL SPECIES IN SOUTHEASTERN-MOST MADAGASCAN RAIN-FORESTS, WITH A REPORT THAT LOWLANDS ARE RICHERTHAN HIGHLANDS IN ENDEMIC AND RARE SPECIES

Replicated elevational transects (maximum range 100-860 m) on three wi dely separated mountains yielded 2430 specimens sorted to 80 conservat ive morphospecies that were assigned to eight major groups. Species we re classified as either rare (< 0.5 % of specimens) or non-rare. Endem ic species, conservatively defined as non-rares that were collected on only one mountain and differed significantly in abundance among mount ains (based on analysis of variance), comprised 13 % of species and we re found only at 100-400 m. Four of the eight major groups had SO % of their rare species found at 100-400 m, 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. Previou sly it has been demonstrated that total land-snail diversity is signif icantly higher in the eastern, windward, coastal mountains (Vohimena C hain) than in the western, leeward, inland mountains (Anosy Chain). Th e present paper shows that this pattern holds (based on analysis of va riance) for four of eight major taxonomic groupings of land snails (ch aropids, 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 'endemic s' (found on only one mountain), which represented 70 % and 80 % of it s species, respectively. Boucardicus, the most diverse group (17 speci es), also showed the greatest variation in geographical and elevationa l ranges. Virtually no species of any group had an elevational range o f less than 200 m. These patterns imply that survey (sufficient at 200 m intervals for snails) and conservation efforts should focus immedia tely on leaf-litter and soil invertebrates of Vohimena Chain forests, including strong emphasis on lowlands. The few remaining forest patche s there are effectively unprotected and are undergoing rapid destructi on by slash-and-burn agriculture.