Large-scale cascaded dam constructions drive taxonomic and phylogenetic differentiation of fish fauna in the Lancang River, China

The establishment of widespread non-native species and the loss of native species driven by multiple anthropogenic disturbances have led to a dramatic reconfiguration of current biodiversity. Trends towards homogenization or differentiation of fish fauna due to the impact of both introductions and extirpations on the taxonomic facet of biodiversity have been observed worldwide, while such effects on the phylogenetic facet have seldom been quantified. Here, we measured the spatio-temporal changes in taxonomic and phylogenetic dissimilarities of fish assemblages among 12 mainstream reaches of the Lancang River against the background of large-scale cascaded dam construction. We found that both the taxonomic and phylogenetic structures of fish assemblages exhibited heterogeneity due to the reduction in the distribution area of common native species and imbalanced invasion by non-native species, which resulted from habitat fragmentation caused by the large-scale cascaded dam construction. Furthermore, changes in taxonomic and phylogenetic dissimilarities were highly correlated. Patterns of fish assemblage based on both taxonomic and phylogenetic structures showed clear spatio-temporal differences due to the imbalance of regional changes, namely, small changes upstream and large changes downstream. This study revealed that taxonomic and phylogenetic dissimilarities could increase in dam-fragmented habitats via imbalanced native species loss and non-native species invasion. Therefore, the risk of a generally positive interpretation of taxonomic and phylogenetic differentiation is highlighted, which should be highly important to ecologists and conservationists.