AVIFAUNAL COMPOSITION AND DISTRIBUTION PATTERNS ALONG ELEVATIONAL GRADIENTS IN THE SUTLEJ AND YAMUNA RIVER BASINS OF HIMACHAL PRADESH AND UTTARAKHAND, WESTERN HIMALAYA, INDIA

Abstract

Understanding the spatial difference in species diversity is a key challenge in ecology (Gaston, 2000). The well-known spatial pattern is the latitudinal diversity gradient, where species richness peaks at tropics and declines towards the poles (Rosenzweig, 1992). The richness of species along the elevational gradients is just a microcosm of the global latitudinal gradient (Rahbek, 1995). Species richness along the latitudinal gradient is the most striking and perhaps best-documented pattern (Yu et al., 2013). The complex elevational diversity of birds has been investigated on every continent (Cavarzere & Silveira, 2012). These patterns of species distribution along elevational gradients vary across taxonomic groups. Species richness patterns along the elevational gradients generally follow three patterns; 1) the monotonic decline of species richness, 2) the hump-shaped pattern with a peak at mid-elevation and 3) increase in species richness with increasing elevation (Figure 1.1). Among these, the first two patterns are the most common ones. i.e. either decreasing richness with increasing elevation or a hump-shaped pattern, in which diversity peaks at mid-elevations (