Responses Of Species And Phylogenetic Diversity Of Fish Communities In The Lancang River To Cascade Hydropower Development

The introductions of nonnative species and disappearance of native species due to the increasing anthropogenic impacts on ecosystems has become the preeminent characteristic of the current biodiversity crisis.Multiple anthropogenic disturbances such as hydropower development,habitat changes,pollution and overfishing have led to a series of undesirable ecological responses in rivers,modifying the structure and function of fish assemblages.Most previous studies have concentrated on the effects of human disturbances on species diversity,but their effects on phylogenetic diversity have been relatively seldom documented.Here,we measured the temporal changes in species diversity and phylogenetic diversity in both alpha and beta diversity of fish assemblages in the Lancang River by fish species lists from historical and current periods.We found that the downstream regions of the Lancang River have experienced a marked loss of native species(average 36.8 species disappeared per region,accounting for 47.2%of the historical native species)in the context of cascade hydropower development,where as few native species disappeared(average 4 species disappeared,accounting for 23.8%of the historical native species)in the upstream regions.In terms of phylogenetic?-diversity,the average taxonomic distinctness(?~+,a taxonomic proxy for phylogenetic diversity)significantly increased in all regions(an increase of 4.4%compared to historical?~+),and the variation in taxonomic distinctness(?~+,a proxy for variation in phylogenetic diversity)significantly increased in downstream regions(24.6%).Meanwhile,in dammed regions,the disappearance rate and rate of change in taxonomic distinctness of native assemblages showed negative correlations with the distances of cascade dams,which provided reference to the cascade hydropower planning.In addition,both taxonomic and phylogenetic beta diversity of fish assemblages in the Lancang River increased significantly,showing heterogeneous trend.Moreover,turnover components of both taxonomic and phylogenetic beta diversity showed significantly increased,which indicated that the proportion of species number and evolutionary branch lengths shared by different assemblages was reduced and that unique to each assemblage increased,while nestedness components of both taxonomic and phylogenetic beta diversity showed significantly decreased,indicating that difference in species and phylogenetic richness between different regions became smaller.In a word,both taxonomic and phylogenetic diversity of fish assemblages in the Lancang River have greatly changed to the intensive hydropower development,especially in its downstream regions.However,the response of phylogenetic diversity to human disturbance was inconsistent with that of species diversity,implying that phylogenetic diversity could provide additional information for assessing the impacts of human domination on fish diversity.