Distribution Pattern of Spiders along an Elevational Gradient in Nelliyampathy Hill Ranges of the Western Ghats, Kerala, India

Systematics provides an essential foundation for understanding, conserving and using biodiversity. Spiders generally have humidity and temperature preferences that limit them to areas within the range of their physiological tolerances, which in turn makes them ideal candidates for land conservation studies. During the course of this study, a quantitative survey of spiders in the Nelliyampathy hill ranges of the Western Ghats was attempted along an elevation gradient, with an aim to investigate the patterns of spider species richness along the elevation gradient. Spiders were collected at a weekly interval for one month at three principal localities along an elevation gradient. The random transect method was used for spider sampling. Time was used as a measure of sampling effort to make the methods comparable. Complementarity and overlap of the spider assemblages at different elevations were assessed using distinctness and beta-diversity indices. This study resulted in the documentation of a total of 515 individuals of spiders belonging to 210 species, 153 genera and 37 families. Among the 210 species collected, 123 species were collected from an altitude of 515-575 m MSL. A total of 101 species were collected from 900-960 m MSL and a total of 51 species were collected from 1325-1375 m MSL. This study revealed that elevation had measurable effect on species richness, with the number of species at three elevations being different. Measures of distinctness and species overlap between elevations were significantly different especially between low elevation and high elevation samples. Analysis of the distribution pattern revealed that diversity varied between elevation gradient, indicating unique species compositions at each elevation. The elevation patterns of species richness are a consequence of many interacting factors, such as plant productivity, competition, geographical area, historical or evolutional development, regional species dynamics, regional species pool, environmental variables and human activity.