Structural and taxonomic correlates of habitat selection by a Puerto Rican land snail

Although terrestrial molluscs make important contributions to the taxonomic and functional diversity of tropical systems, little is known about their ecology. Caracolus caracolla is a large terrestrial snail, common in a wide variety of habitats on Puerto Rico, including the tabonuco rain forest. To determine if this snail exhibits habitat selection, we surveyed 19 taxonomic and structural attributes of the understory, as well as snail abundance, in 60 sites within the tabonuco rain forest during the dry season. Caracolus caracolla had a clumped spatial distribution, and was associated more often than expected by chance with the shrub, Piper glabrescens, and less often than expected on three other common understory plants. Although much of the variation in snail 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 spatial distribution of C. caracolla was linked to microhabitat conditions that reduce the likelihood of desiccation. We hypothesize that smaller snails occupy areas of the understory where the likelihood of desiccation is reduced, whereas larger individuals, less encumbered by physiological constraints related to desiccation, expand their niche to include upper reaches of the understory where they take advantage of additional resources and enhance the likelihood of mate encounter.