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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]

The statistical background for the relationship between the taxonomic diversity of macrozoobenthos and water mineralization is presented in the example of the benthic communities of plain rivers in the Lower Volga River basin. Significant differences have been found for a complex of 35 indices of species and phylogenetic α- and β-diversity in the tributaries of the Saratov and Volgograd reservoirs compared to the saline rivers of the Elton Lake basin. The hypothesis of phylogenetic niche conservatism [5] is confirmed by a significant effect of phylogenetic overdispersion at low and medium salinity of watercourses and phylogenetic clustering at high water salinity. Mean salinity tolerance has been assessed for each of the 356 species considered; this index was interpreted as the statistical probability of inhabiting the waters of certain mineralization by particular species. A statistically significant phylogenetic signal corresponding to the species traits was revealed by Pagel's lambda and Bloomberg's K tests. Mean salinity tolerance for taxa of various systematic levels has been presented as a cladistic tree. [ABSTRACT FROM AUTHOR]