Aims To (1) describe the distribution patterns of land‐snails occurring in afromontane forest habitats on Mount Kenya, in relation to elevation and aspect; (2) explore the relations between the land‐snail faunas and environmental conditions within the forests. Location Mount Kenya, Kenya. Methods Molluscs were sampled using standardized direct search and litter sieving methods in a total of sixty‐four replicated plots along four elevational transects spanning an altitudinal range from 1782 to 2851 m on the east, west, south and north‐northwest sides of Mount Kenya. Elevation, vegetation type, forest structure, soil calcium, soil pH, mean annual rainfall and other environmental variables were measured on each plot. Correlation and joint regression analysis, and canonical correspondence analysis (CCA) were used to relate snail diversity and abundance, and faunal composition, to site elevation and other environmental variables. Results Sixty‐eight mollusc species were recorded during the study with transect totals between thirty‐four and fifty‐three species. Mean number of species and mean snail abundance ranged from 6.75 to 23.0 and 19 to 348 per plot, respectively. Overall, species richness and Shannon diversity index declined with increasing elevation. Snail abundance declined with increasing altitude along three transects and was positively related to soil pH and soil calcium, but species richness was not. Several species exhibited clear altitudinal distribution patterns. Mean annual rainfall varies greatly around the mountain and tends to decrease with altitude over the elevational range studied. Soil calcium and pH were negatively related to annual rainfall. Estimated mean annual rainfall accounted for the greatest variation in the mollusc fauna around the mountain. Faunas in forests on the drier, western side of Mount Kenya contained higher numbers of species in families that are characteristic of temperate latitudes, whereas tropical families were more prevalent on the wetter, south and east sides. Main conclusions Land‐snail diversity in Mount Kenya’s forests declines with elevation and thus follows the widespread pattern shown by most groups of organism. However, faunal variation appears to be more closely related to rainfall levels, than to altitude per se or the other environmental variables examined. The effects of rainfall on snails could either be direct, or indirect via its effects on soils or vegetation, but the study suggests that direct effects are more important. Indirect effects mediated by changes in soil chemistry appear to be less important because lower altitude sites with more strongly leached and acidic soils tend to have richer and more abundant snail faunas. The reason for the association of temperate latitude mollusc families with forests on the drier, western sides of the mountain is not clear. The number of mollusc species present in Mount Kenya’s forests is broadly comparable with that reported elsewhere in East African forests. However, overall, the data from this study and elsewher...

Rowson, B., Tattersfield, P. & Symondson, W. O. C. (2010). Phylogeny and biogeography of tropical carnivorous land‐snails (Pulmonata: Streptaxoidea) with particular reference to East Africa and the Indian Ocean. —Zoologica Scripta, 40, 85–98. A phylogeny is presented for the speciose, near pan‐tropical, carnivorous achatinoid land‐snail superfamily Streptaxoidea inferred from DNA sequences (two nuclear and two mitochondrial regions) from 114 taxa from Africa, the Indian Ocean, Asia, South America and Europe. In all analyses, Streptaxidae are monophyletic, while the (two to six) previously recognised subfamilies are polyphyletic, as are several genus‐level taxa including the most speciose genus Gulella, necessitating major taxonomic review. The Asian Diapheridae are sister to Streptaxidae, which forms several well‐supported clades originating in a persistent basal polytomy. Divergence dating estimates, historical biogeography, and the fossil context suggest a Cretaceous origin of these families, but suggest Gondwanan vicariance predated most radiation. The basal polytomy dates to the Paleogene and may correspond to a rapid radiation in Africa. There is evidence for multiple Cenozoic dispersals followed by radiation, including at least two from Africa to South America, at least two from Africa to Asia and at least two from Africa to Madagascar, indicating Cenozoic turnover in tropical snail faunas. The endemic Seychelles and Mascarene streptaxid faunas each are composites of early Cenozoic lineages and more recent dispersals from Africa, with no direct evidence for an Asian origin as currently proposed. Peak streptaxid diversity in East Africa is explained by Neogene speciation among a large number of coexisting ancient lineages, a phenomenon most pronounced in the Eastern Arc‐Coastal Forests centre of endemism. This includes Miocene diversification in Gulella, a primarily East and South‐East African group which remains strikingly diverse even after unrelated ‘Gulella’ species are reclassified.

We sampled terrestrial molluscs at fifteen elevations between 400 and 2000 m in Mwanihana Forest Reserve, Tanzania and recorded 84 taxa. Four diversity measures – species density (DP), species richness (D20) and observed (SO) and interpolated (SI) alpha diversity – were measured; beta diversity and abundance were also investigated. Mean elevational range was 470 m. DP, D20, alpha diversity and mollusc abundance increased with elevation, but alpha diversity peaked at 1695 m (SO) or 1500 m (SI) and declined at higher elevations. Maximum beta diversity was at 1000 m. Soil pH was negatively correlated with elevation and DP. Cluster analysis divided the sites into lowland (400–900 m) and highland (>1000 m) groups. Axis 1 of a canonical correspondence analysis was associated with altitude and suggested a faunal discontinuity at 1000 m. Variation within the highland (>1000 m) and lowland faunal sets was related to elevation and forest structure respectively. The findings indicate that mollusc diversity peaks at intermediate elevations. This may be related to the combined effects of low rainfall conditions at low elevations and increasing effects of soil leaching at high elevations, both of which may limit mollusc diversity and abundance. Diversity at intermediate altitudes may be further elevated because of faunal mixing of lowland and highland groups.

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