Influence of stream habitat variables on distribution and abundance of tadpoles of the endangered Purple frog, Nasikabatrachus sahyadrensis (Anura: Nasikabatrachidae)

Abstract

The rheophilous tadpoles of the rare and endangered Purple frog, Nasikabatrachus sahyadrensis (Biju and Bossuyt, 2003), have suctorial mouthparts that enable them to occupy a very unique microhabitat within torrential streams. In this study, we examined the influence of four stream habitat variables, i.e. water flow velocity, slope of substrate, depth of water column and water temperature, on the distribution and abundance of these tadpoles. A total of 204 measurements were recorded for all the four variables in 68 marked grids along a 100 m section of two selected streams. Statistical analysis showed that water flow velocity was the best predictor for abundance of tadpoles in both streams. When the number of tadpoles was modeled as a function of each environmental variable, the relationship ranged from linear (w.r.t water flow velocity and water temperature) to unimodal humped curves (w.r.t slope of substrate and depth of water column). The results were further assessed with respect to distribution and behavioral observations of the tadpoles in the streams as well as to the threat posed by dams and reservoirs on tadpole microhabitats.