Natural leaf packs and invertebrates in a tropical stream: Is there a functional relationship?

Naturally occurring leaf packs in five sites along the elevation gradient in Eswathu Oya stream in Sri Lanka were sampled and analysed for species composition of leaves and benthic macroinvertebrates. Eswathu Oya is a perennial, low order, mountain stream in the wet climatic zone of Sri Lanka. Leaves of only five species of plants were found in all sites – Hevea brasiliensis, Ochlandra stridula, Alstonia macrophylla, Terminalia arjuna and Melia azedarach. In each sampling site Hevea brasiliensis and Ochlandra stridula leaves were found in higher abundance. The contribution of other leaves varied with the site. Diptera larvae of the family Chironomidae, were the dominant group of leaf colonizing animals. The relative abundance of Chironomidae decreased along the elevation gradient in the down-stream. Gathering Collectors (GC) were the dominant functional feeding group (FFG) found in all leaf packs, but their abundance decreased along the downstream elevation gradient. Shredders were not present, as reported from some other tropical streams. Predators and Scrapers were increased along the downstream gradient. Filtering Collectors and Pierce-Herbivores did not show a clear pattern. The study documents that macro invertebrate communities responded to change in water quality, availability of leaves and their nutritional quality along the elevation gradient in Eswathu Oya, Sri Lanka.