LAND SNAIL FAUNAS OF THE NAPIER AND OSCAR RANGES, WESTERN-AUSTRALIA - DIVERSITY, DISTRIBUTION AND SPECIATION

The snail faunas of the Napier and Oscar Ranges, Western Australia have two major components: large camaenid species which are restricted endemics, with tiny geographical distributions and a pattern of geographical replacement within the Ranges, and smaller species of wider distribution, most of which are found throughout the Ranges. Sampling of 55 similar sites, protected from fire, over the length of the Ranges reveals this pattern clearly, with γ diversities being far higher for camaenids than for others, in which there is no pattern of geographical replacement. This difference is not found in temperate and subtropical snail faunas from elsewhere, nor does the camaenid pattern occur in surveys of diversity in other organisms. These results are discussed in terms of dispersal and allopatric speciation related to demonstrable environmental fluctuation. An additional finding is that within one major taxonomic group (Gastropoda), a community may be partly structured by competition and exclusion and partly by accidents of colonization and accumulation: some, but not all niches may be full. Copyright © 1992, Wiley Blackwell. All rights reserved