Altitudinal patterns in benthic macroinvertebrate distribution in the Rio Siniguis

E.S. Sokol¹, J.D. Allan², and A.S. Flecker³. ¹Virginia Polytechnic Institute and State University, Blacksburg, VA, USA, 24061-0406, ²School of Natural Resources and Environment, University of Michigan, Ann Arbor, Michigan, USA, 48109-1115, ³Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, USA, 14853-2701

We examine altitudinal gradients in benthic macroinvertebrate assemblages in the Venezuelan Andes, within a pristine stream ecosystem that may serve as a reference system for the region. The benthic macroinvertebrate community of the Rio Siniguis was sampled at 9 sites along an altitudinal gradient ranging from 360m to 3725m. Benthic macroinvertebrates were characterized at each site in terms of abundance, richness, evenness, and functional feeding group metrics. In general, the macroinvertebrates of the Rio Siniguis were dominated by Diptera, Ephemeroptera, Plecoptera and Trichoptera. Lower altitude sites (below 2600m) were characterized by a higher ratio of EPT to Diptera. Predators, gatherers, filterers and scrapers were present at all sites; however, shredders were not observed above the 2600m site. Mid-altitude sites exhibited highest benthic macroinvertebrate densities. Ephemeroptera and Plecoptera abundance both exhibited a strong positive relationship with elevation, with correlation coefficients of 0.84 and 0.72 respectively. Abundance, richness, and evenness showed no significant pattern with elevation. The benthic communities and general trends observed in the Rio Siniguis were comparable to those documented in other larger scale South American studies.