Tracing climate change with riverine ecotones and macroinvertebrates: is there need for extended monitoring at low elevations in western Himalaya?

Abstract

River ecosystems in Himalaya are changing rapidly as glaciers continue to recede at a pace faster than rest of the globe. We delineate riverine ecotones along an elevational gradient in the western Himalaya by examining community turnover of freshwater macroinvertebrates. Using the Threshold Indicator Taxa Analysis (TITAN), we provide a set of indicator macroinvertebrate taxa that represent the altitudinal band of greatest community turnover. Out of a total of 31 taxa, 11 were identified as indicators, responding either positively (n = 2) or negatively (n = 9) to altitude. Further, assessments of community turnover points toward a potential ‘riverine ecotone’ for the western Himalayan streams at an altitudinal band of 1442–2447 m above sea level (asl). As ecotones are transitional bands that harbour communities most sensitive to climate change, we further compared them across different latitudes of Himalaya to ascertain the differences in climate sensitive zones across latitudes. Our comparisons reveal that as we move towards higher latitudes in the Himalaya, the climate sensitivity drops to a lower elevational range of 1442–2447 m above sea level at 31° 33′–31° 43′ N. In contrast, at lower latitudes (27° 51′–28° 23′ N) the riverine ecotones have been recorded at a much higher elevation of 2900–3500 m above sea level. Through our study, we delimit that lower elevations in western Himalaya warrant concentrated long-term monitoring efforts to track species responses to climate change. Our comparisons of riverine ecotones along latitudes unlock new insights to understand the macroecology of community turnovers in riverine ecosystems.