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Abstract—The authors discuss the use of the Greenell concept of ecological niches to analyze the taxonomic structure of communities and their relationship with environmental factors. The modeling of ecological niches was carried out using the results of 30-year studies of macrozoobenthos communities on 90 small and 12 medium-sized plain rivers in the region of the Kuibyshev, Saratov, and Volgograd reservoirs. Geoclimatic indicators, relief characteristics, and hydrochemical assessments of the water quality at sampling points were considered as abiotic factors, where 11 variables with the least collinearity were selected. The multidimensional space of the initial abiotic factors was projected onto the orthogonal axes of the first two principal components; ordination diagrams with plotted points of the presence of species were constructed. The model of the potential ecological niche of each species was represented as an area in the space of latent variables, in which the habitat suitability index Z estimated by the probability density of occurrence corresponds to the given constraints. The authors used the Schoener and Hellinger indices to quantify the proportion of overlapping niches belonging to two different benthos taxa. The matrix of distances between overlapping niches was formed for all possible paired combinations of the 40 most ecologically significant macrozoobenthos species. Cluster analysis of the obtained distance matrix was carried out by the methods of hierarchical agglomeration and fuzzy k-means. In the general multidimensional space of abiotic variables of the region studied, four areas of collective niches for groups of species with maximum distances between their centroids were identified. The analysis of intergroup variation of environmental factors is given, and the characteristic features of each group are discussed: ecological strategy, biological traits, and tolerance level. [ABSTRACT FROM AUTHOR]