Experimental Assessment of the Effects of Environmental Factors and Longitudinal Position on Alpha and Beta Diversities of Aquatic Insects in a Neotropical Stream

We evaluated the effect of environmental factors on the abundance and genera richness of aquatic insects colonizing artificial substrates. We also assessed the relative effects of environmental factors on assemblage variation (beta diversity), and contrasted its magnitude with the variation associated with the spatial position of reaches in a Neotropical stream. Homogeneous and heterogeneous bricks were installed in seven stream reaches and removed after 60d. Substrate type and organic matter showed significant effects on abundance. For observed richness, substrate type was the only important variable. For rarefied richness, no explanatory variable was important. A NMDS ordination of bricks revealed the effect of spatial position and substrate type. A partial Redundancy Analysis (pRDA) indicated that the environmental matrix explained 12.44% of the total variation, while reach position explained 7.41%. We conclude that at local scale (reaches 430-920 m apart), environmental factors, especially substrate heterogeneity, were important in determining the alpha and beta diversities of the insect assemblage in the stream. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim