How altitudinal gradient affects the diversity and composition of benthic insects in arid areas streams of northern East Algeria

This study was carried out to evaluate the variation of diversity and composition of benthic insects in streams, along an altitudinal gradient in an arid area of Belezma National Park, Northern East of Algeria. Benthic entomofauna was sampled in the spring season of 2015, 2017 and 2018 at 28 sampling sites distributed along 4 streams unaffected by human pressure. The altitudinal gradient varies between 1045 m and 1500 m. At each site, we measured 5 physicochemical parameters of water and other physical factors describing each site (velocity, depth and width). All of these environmental factors vary significantly with altitude. A total of 78 taxa belonging to 55 families and 8 orders of benthic insects were identified. Both diversity and abundance of studied entomofauna vary with altitudinal gradient. The highest values of diversity were found in the fourth altitudinal zone (AZ4: up to 1400 m, total taxa richness = 52) and AZ3 (1300 to 1400 m, Shannon index = 3.16). The average number of individuals in AZ1 is higher than in all the other altitudinal zones (mean individuals number = 102.75). The General Linear Model analysis shows that the altitudinal gradient is in favour of high diversity but in disfavour of population abundance. The hierarchical clustering analysis revealed three cluster groups of benthic insects, which are altitudinal indicators. Diptera and Ephemeroptera in downstream stations are mainly replaced by Coleoptera in upstream ones.