EFFECTS OF TREEFALL GAPS ON THE DENSITY OF LAND SNAILS IN THE LUQUILLO-EXPERIMENTAL-FOREST OF PUERTO-RICO

The effect of disturbance on land snail density in a montane subtropical wet forest was evaluated during wet (March-April) and dry (June) seasons by collecting specimens from quadrats positioned along transects that bisected treefall gaps in the Luquillo Experimental Forest of Puerto Rico. Atmospheric and litter temperature, relative humidity, litter and soil moisture, slope, and substrate type also were measured in each quadrat to determine the effect of these environmental parameters on the spatial distribution of the land snails during two sampling periods in 1989. Of the 34 species of snail known from the forest, only five occurred with sufficient frequency to permit statistical analysis. The abundances of three species (Austrosolenites alticola, Megalomastoma croceum, and Subulina octana) were not significantly different in gap versus nongap areas. In contrast, Nenia tridens and Caracolus caracolla responded to patches created by treefalls. In particular, the abundance of N. tridens was significantly higher in gaps; whereas, that of C. caracolla was significantly higher in the surrounding undisturbed forest. Such differences in distribution may be attributable to factors related to diet and body water loss rates.