Abstract:

Identifying how fish assemblages in upland streams respond to environmental changes and anthropogenic activities is the basis for the conservation and management of upland stream systems and fish diversity. Based on data collected from 78 sampling sites (including 39 impounding areas and 39 free-flowing segments, respectively) associated with 39 low-head dams in four 1st-order streams of the Qingyi basin in Anhui Province, we investigated the effect of low-head dam on the habitat homogenization and the biotic homogenization of fish assemblages in upland streams. A total of 27 species representing 10 families and 5 orders were collected, among which 23 and 27 species were collected from the impounding and free-flowing areas, respectively. Principal coordinate analysis (PCoA) and canonical analysis of principal coordinates (CAP) results showed that the local habitat differed significantly between impounding and free-flowing areas, the former characterized by relatively low substrate coarseness and heterogeneity and the latter showing shallower water depth and width. Permutational analysis of multivariate dispersions (PERMDISP) result indicated that the heterogeneity in spatial variability of the local habitat was significantly lower in the impounding areas than the free-flowing areas, suggesting habitat homogeneity in the impoundments of low-head dams. The variations in the coefficient of similarity of fish assemblages in the impoundments relative to that found in the free-flowing segments were consistent across the four study streams and the two sampling seasons. Compared with that in the free-flowing segments, the between-assemblage similarities for fishes in the impoundments either increased or decreased, of which ΔCS_J was negatively related to the initial similarity of fish assemblages. ΔCS_J was positive when the initial similarity was lower than 50%, while ΔCS_J was negative when the initial similarity was more than 50%. Our results suggest that low-head dams may decrease the spatial variability in local habitat within the impounding areas of dams and result in the homogeneity of the local habitat. However, the variations in fish assemblages within these impoundments include two ecological processes, i.e., biotic homogeneity and heterogeneity. The biotic homogeneity/heterogeneity depends on the size of the initial similarity between different assemblages. The assemblages showing relatively low initial similarity will be homogenized and those of high initial similarity will be heterogenized.

Key words: habitat homogenization, biotic homogenization/heterogeneity, stream fishes, low-head dam