Acidophilic terrestrial gastropod communities of North America

Habitats with soil pH < 4 and Ca < 100 ppm, such as pocosins, Sphagnum bogs and heathlands, would appear inimical to land-snail biodiversity. Nevertheless, a survey of 1,356 sites, c. 1/2 million individuals and over 240 species (c. 1/5 of the continental fauna) across North America shows that c. 10% of species appear to favour such highly or moderately acidic sites, spread from subtropical forests of the Gulf of Mexico coast to the arctic tundra. Nonmetric multidimensional scaling ordination of faunas from 292 sites that support at least five co-occurring species documents that the principal axis of compositional variation in highly and moderately acidic habitats is significantly (P < 0.0005) correlated with latitude, while the second axis is significantly (P < 0.0005) correlated with moisture level. Composition was found to vary continuously along both axes, implying that discrete acidophilic communities are not present. While highly and moderately acidic sites were shown to have significantly (P < 0.000000005) lower richness and abundance compared with neutral/calcareous habitats, even the most acidic sites still typically supported 5-10 species. Abundance distributions in highly acidic habitats were found to be more uneven those of neutral/calcareous sites. The greater richness of the North American acidophilic land snail fauna compared with that in Europe has allowed communities to display replacement-driven compositional turnover. These results demonstrate that it is vitally important for biodiversity surveys of North American land snails not to ignore acidic habitats, because they harbour an important and surprisingly diverse fauna.