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Session11: Land use, urban planning

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  Chairman: Prof. Patil H. S

Rapporteur: Sudhira H. S

Damming the Sharavathi River: A Boon or A Bane for Biological Diversity? An Indicator Approach through Ants

Ajay Narendra


The usual taken for granted idea of loss of biological diversity with the construction of a dam has been investigated at the Sharavathi river basin in this study. The Linganamakki dam was constructed over the river Sharavathi for hydroelectric purposes in the early 1960s. The undulating topography in the region has resulted along with submergence of vast land area, creation of islands of varying areas within the reservoir (30 of which harbour vegetation comprising mainly of evergreen, semievergreen and moist deciduous forests). To determine the state of these islands, ants, one of the well established biological indicators were sampled in ten randomly picked islands. A one time sampling was carried out using standard collection methods of pitfall traps, leaf litter collections, bait traps and visual collections. Comparison of the species composition between the islands and the river basin (earlier work) revealed that islands harboured a composition of ants that had highly specific niche requirements as Harpegnathos saltator (endemic species) and Leptogenys processionalis. The overlapping canopy cover in the islands prevented the occurrence of Pachycondyla rufipes, a canopy gap specialist. The highly undisturbed islands had very low levels of human interference quite unlike the river basin, thereby not providing shelter to the invasive species Anoplolepis longipes. Areas that do get submerged when the reservoir is full, but dry (presently), due to lack of rains show the presence of a hot climate species Camponotus sericeus that were abundant in scrub jungles and savanna grasslands of the river basin. Broad leaves and shady areas being the characteristic of most of the forests of the islands, supported O.smaragdina that thrives in such niches only. Polyrhachis mayri, yet another arboreal species, known to prefer undisturbed evergreen and moist deciduous forests in the river basin, were extremely abundant in the islands. Both the arboreal species of ants never known to nest on neighboring trees, showed several such occurrences in some islands, hinting at a high degree of competition in the islands. Moist deciduous forests in islands cut to pave way for Acacia plantations (MPM) harboured a different composition dominated by a specialist predator Diacamma rugosm, known to be one of the most dominant ants of an acacia plantations in the river basin. The arboreal species of ants were totally absent from Acacia plantations except in the few remnants of moist deciduous trees (in the same island) that provided niches for Oecophylla smaragdina. Thus probably reducing its earlier wide distribution into the present few trees. The arboreal ant fauna being extremely abundant along with the presence of species preferring undisturbed dense forests coupled with the absence of invasive species suggests the islands are biologically rich. The river basin however affected by anthropogenic activities have posed a serious threat to conservation evident by abundant distribution of invasive species, hot climate species and canopy gap specialists. Damming the Sharavathi has isolated and over time has managed to create biologically rich habitats for ants in the islands that have lasted till now due to their inaccessibility.

Address: Centre for Ecological Sciences,  Indian Institute of Science, Bangalore, 
Karnataka, India Email: