Nestedness pattern in freshwater fishes of the Western Ghats: an indication of stream islands along riverscapes

Fragmented habitats exhibit distinctive patterns of species richness and species composition. They often exhibit patterns of pronounced nestedness, wherein the species present in comparatively depauperate locations represent statistically proper subsets of those present in locations that are richer in species. The current study has been conducted on the freshwater fishes of Sharavathi River, considering 41 stream and reservoir sites with 261 sampling events to understand the nestedness pattern in fish communities. Of the 64 fish species collected, 39 are from the reservoir and 33 from the stream islands. For the species of the stream islands, including the reservoir fishes in the stream, the nestedness index, T was 8.27°C, while species exclusive to stream islands had T = 10.5°C. In contrast, in species that are common to both stream islands and the reservoir, T was 0.37°C. Relatively higher T in the exclusive stream species composition implies that they are highly depauperated due to fragmentation in the streams and its negative influence on the stream fish communities.