STRUCTURAL AND TAXONOMIC CORRELATES OF HABITAT SELECTION BY A PUERTO-RICAN LAND SNAIL

Although terrestrial molluscs make important contributions to the taxo nomic and functional diversity of tropical systems, little is known ab out their ecology. Caracolus caracolla is a large terrestrial snail, c ommon in a wide variety of habitats on Puerto Rico, including the tabo nuco rain forest. To determine if this snail exhibits habitat selectio n, we surveyed 19 taxonomic and structural attributes of the understor y, as well as snail abundance, in 60 sites within the tabonuco rain fo rest during the dry season. Caracolus caracolla had a clumped spatial distribution, and was associated more often than expected by chance wi th the shrub, Piper glabrescens, and less often than expected on three other common understory plants. Although much of the variation in sna il density (73.4%) appeared unrelated to habitat descriptors, patches of forest with abundant ground cover at 0.15 m or high plant apparency (foliar development) at 1.98 m harbored high snail densities. The spa tial distribution of C. caracolla was linked to microhabitat condition s that reduce the likelihood of desiccation. We hypothesize that small er snails occupy areas of the understory where the likelihood of desic cation is reduced, whereas larger individuals, less encumbered by phys iological constraints related to desiccation, expand their niche to in clude upper reaches of the understory where they take advantage of add itional resources and enhance the likelihood of mate encounter.