Micro-Habitat Preferences of Litter-Dwelling Land Snail Communities along an Elevation Gradient in the Upper Catchment of Walawe Basin in Sri Lanka

Abstract

Sri Lanka is reported with highly diverse and endemic land snail fauna. Nevertheless, it is greatly under sampled while data are scarce on their micro-habitat preferences, which are critical for land snail conservation decision making due to their limited mobility and high susceptibility to predation. Here we have investigated the micro-habitat factors that influence variation of species richness and diversity of land snail fauna along an elevation gradient from 100 m to 2,200 m, in order to see whether those malacofaunal communities differ significantly with the elevation dependent features of their micro-habitat. The investigation was conducted along a transect from Udawalawe to Horton Plains National Parks in the upper catchment of the Walawe basin in Sri Lanka, by collecting specimens through time restricted searches within twelve 10×10 m quadrats, from November 2017 to February 2018. Nine micro-habitat variables viz. soil moisture, soil pH, litter depth, soil temperature, air temperature, canopy cover, undergrowth cover, dead-wood content and tree density were measured for each quadrat. Correlation analysis followed by regression was used to establish the relationships between the micro-habitat variables and land snail species richness, diversity, percentage endemism and threatened percentage. The present study populated a database of 770 records of live land snails and shells of dead specimens, representing 33 species belonging to nine families, with 80% of species endemic to Sri Lanka, including a possibly undescribed Cyclophorid. Family Ariophantidae (13 species; 55.7%) represented the highest number of specimens including the most abundant species (Euplecta acuducta; 16.8%), followed by Glassulidae (5 species). The results of the present study reveals that micro-habitat variables directed by the elevation have influenced the land snail richness and diversity variation along the transect. Increasing litter depth (r=0.71; p=0.01) and tree density (r=0.771; p=0.003) were recorded to highly influence the species richness, while the land snail diversity (Simpson Index) had a strong relationship with the soil moisture content (r=0.719; p=0.003). Percentage species endemism of land snails was highly correlated with the soil moisture (r=0.798; p=0.002) and the soil temperature (r=0.786; p=0.002). Canonical Correspondence Analysis identified soil temperature, litter depth and soil moisture as the major micro-habitat variables associated with land snail distribution while indicator species have been identified for each micro-habitat variable.
Keywords: Land snail, Micro-habitat, Species diversity, Walawa basin