Distinctive patterns in habitat association and distribution of tiger beetles in the Shivalik landscape of North Western India

摘要

The purpose of the paper is (a) to describe the distribution pattern of tiger beetles in Shorea robusta dominated forest ecosystems at landscape level of north western Shivalik Himalaya in environmental space and (b) to evaluate the nature of microhabitat association amongst recorded species of tiger beetles. Twenty-five species of tiger beetles belonging to ten genera were recorded from six protected areas in the tropical dry deciduous Shivalik region with an altitudinal gradient of 350–1,400 m above mean sea level in north western India. Sampling for tiger beetles was carried out using strategically designed sample plot in ten distinct habitat types with five collection methods employed. Species composition of tiger beetles varied significantly between microhabitat types of the protected areas (Shannon H′ = 0.436–1.069) and habitat specialists were found in only few of habitats. Bray–Curtis cluster analysis clustered the ten habitats into five cluster groups based upon the species composition with Shorea robusta most distinct from agricultural habitats. Riverine area was found to be the most diverse (with 18 or 72% of total species) as well as abundant (457 ± 33.61 SE individuals recorded per sample plot). Khair, Syzygium and pine forests were least rich and had only three species each. Two species J. crassipalpis and M. melancholica were found only in riverine habitat. Though late summer to mid-monsoon was found most favorable for tiger beetles, only one species, C. chloris was persistently found even during modest winter months. Bulla’s diversity index showed that habitat breadth of species ranged from 0.00 to 6.66, an indicative of their habitat restrictiveness. Indicator species analysis revealed as many as 14 species indicative of particular habitat conditions. Descriptions of some important ecological and behavioral aspects are included for these species. The observed C-score (299.43330) showed that there is less co-occurrence among species pairs alongwith lower niche overlap (Pianka’s index = 0.14191) thereby illustrating ample resource partitioning at microhabitat level. Further, co-occurrence index among guilds (C-score = 213.16250 with variance 1,949.76300) was found to be smaller than expected, revealing that feeding guilds are differing significantly from one another in their levels of co-occurrence. Canonical correspondence analysis identified canopy cover, litter and average tree density as the most important habitat variable defining the distribution of tiger beetles in environmental space. Such assemblage patterns among species of tiger beetle would thus provide a solid basis to interpret changes in microclimatic conditions, caused by humans directly or through long term climate change and would thus help establishing a baseline in long term monitoring of these forest ecosystems.