We have studied the habitats occupied by snails of the genus Partula on the island of Moorea in French Polynesia. Discriminant analysis of samples containing two, three or four sympatric species shows that the taxa divide the available habitat so that each predominates in its own characteristic environment. The most important factor determining the numbers of species within habitats is the density and size of the climbing pandanus plant Freycinetia. Although all the species can use this plant, `specialists' restrict its occupation by `generalists'. The number of species at any locality depends on the habitat, but the particular array of species seems to be influenced both by interspecific interactions and by the history of colonization.