Variación espacial de la composición y diversidad de géneros de Ephemeroptera (Insecta) en un río tropical altiandino

Abstract

The composition of the benthic macroinvertebrates in stream habitats is influenced mainly by the quality of the substrate and the current. The riffles are stable lotic habitats, with heterogeneous substrates and detritus accumulation that should maintain abundant and diverse communities. However, in mountain streams diversity doesn’t seem to differ among given habitats, by the predominance of the gravels, boulders and cobbles of varied size. With the purpose of proving these hypotheses, composition and the diversity of the nymphs of the Orden Ephemeroptera in rapids and pools of the stream La Picon, Merida State, located 2 274 m above sea level into Sierra Nevada NP were analyzed comparatively. During one year, with a biweekly frequency, three samples of the benthos for each habitat were collected using Surber Net. Jointly with the sampling of the fauna, the current was measured and samples of fine organic matter were collected. Current and fine organic matter differed significantly between habitats (Mann-Whitney P≤ 0.01). According to PCA, for the Orden Ephemeroptera, the composition differed between riffles and pools, prevailing in the first: Baetodes, Leptohyphes, Prebaetodes, Thraulodes and Andesiops, and in the second Haplohyphes, Farrodes, Trichorythodes, and Americabaetis. The largest mayfly density was observed in the riffles (Mann-Whitney p ≤ 0.05). Diversity based on numbers of Hill didn't evidence differences between both habitats (Mann-Whitney: p>0.05). As for the whole macroinvertebrates community the TWINSPAN revealed particular associations among taxa, for each habitat and for each sampling date.