Patterns of abundance, species richness, habitat use and morphology in tropical terrestrial molluscs: effects of disturbance and elevation

Spatial variation resulting from natural disturbances and elevational gradients is of particular importance to the distribution and abundance of organisms that are sessile or of low vagility. This study examined the influence of disturbance, in the form of canopy openness, and elevation on the terrestrial mollusc fauna of the Luquillo Experimental Forest (LEF) of Puerto Rico. Of 14 species of terrestrial molluscs collected in the LEF, only Polvdontes acutanqula and Platvsuccinea portoricensis responded to canopy openness. Moreover, significant responses to canopy openness did not diminish with increasing elevation. This limited response to canopy openness by particular species was reflected in the absence of significant differences in species richness between categories of canopy openness. Nonetheless, significant differences in abundance associated with elevation were detected in all but one species, Alcadia striata. Regardless of elevation, densities of all species of land molluscs, except for Gaeotis niqrolineata were higher in the wet than in the dry season. Mean species richness also increased significantly from the dry to the wet season, peaking at an elevation of 400 m in both seasons. The elevational pattern in species richness of land molluscs appears to be related to changes in temperature. Mean elevational range size increased with elevation. Land molluscs in the LEF, particulahy G. niqrolineata. exhibited a strong affinity for the palm, Prestoea montana. Seasonal and elevational differences in substrate associations of land molluscs also were detected. Finally, the relationship between body size and elevation differed among species of land molluscs. Of those with ranges spanning the entire elevational radient (200 m to 1000 m), most showed a positive relationship between body size and elevation.