LOCAL PATTERNS OF LAND SNAIL DIVERSITY IN A KENYAN RAIN-FOREST

Terrestrial molluscs were sampled in indigenous forest and plantation plots in Kakamega Forest, western Kenya, which is the eastern-most pat ch of Guineo-Congolian rain forest in Africa. Fifty species (one slug and 49 snails) were recorded from 27 indigenous forest plots, and the mean species per plot was 23.4. The majority of the species present in the fauna were small, litter dwellers, with 52% having a major shell dimension of less than 5 mm. Overall, species richness and faunal comp osition were relatively uniform throughout the forest system. However, forest edge plots, including plots located along large rivers and in smaller blocks of forest, had a deficiency of some minute, litter-dwel ling species but supported a higher frequency of some large-shelled ta xa. The four plantations sampled supported fewer species per plot (15. 25 species/plot) and also lacked several of the small, litter-dwelling species found in the indigenous forest. Many other species of mollusc have been previously reported from Kakamega Forest. The reported moll usc fauna of Kakamega Forest represents about 5.8-9.5% of the total kn own East African forest mollusc fauna, thus suggesting that there must be considerable taxonomic replacement of species throughout the regio n. The recorded molluscan diversity in Kakamega Forest is high in a wo rldwide context. Kakamega Forest is not old in geological terms, the L ake Victoria basin having received a much more arid climate during per iods of extended glaciation at higher latitudes. Its forest fauna must have colonised since the last glacial maximum in Africa, approximatel y 14000 years BP; the composition of the recorded fauna supports the v iew that recolonisation was mainly from forest refugia in central Afri ca. The conservation implications of the findings are discussed.