3.3 Community similarity
Overall, both the taxonomic and functional similarities of fish
assemblages differed significantly between the impoundments and
free-flowing segments (P <0.001). Specifically, the
taxonomic similarity of fish assemblages was significantly lower in
impoundments than that in free-flowing segments, whereas the functional
similarity of fish assemblages was generally higher in impoundments
(Figure 4). Meanwhile, an opposite trend was detected between the
changes in taxonomic and functional similarities, i.e. taxonomic
differentiation (taxonomic ΔCS: −2.09% ± 21.89%) was accompanied by
functional homogenization (functional ΔCS: 4.05% ± 13.03%) in stream
fish assemblages.
Mantel tests showed that changes in taxonomic and functional similarity
were positively correlated (r =0.33, P <0.001;
Figure 5b). Furthermore, Chi-square tests showed that the observed
percentages of taxonomic ΔCS and functional ΔCS (i.e. differentiation
and homogenization) for
pairwise
assemblages were statistically significant
(χ2 =140.1, df =1,P <0.001). Among the 1,378 pairwise assemblages, 64.73%
(892 comparisons) showed uniform changes between taxonomic ΔCS and
functional ΔCS, of which 36.14% pairs (quadrant I: 498 comparisons)
presented both taxonomic and functional homogenization and 25.11% pairs
(quadrant III: 394 comparisons) showed differentiation
(Figure 5b, Table 3). However,
35.27% (486 comparisons) showed differences between taxonomic ΔCS and
functional ΔCS. Specifically, 25.11% pairs (quadrant II: 346
comparisons) showed taxonomic differentiation but functional
homogenization, and 10.16% pairs (quadrant IV: 140 comparisons)
presented the opposite changes (Figure 5b, Table 3).