Low-head dams facilitate the native invasion of downstream fishes to subtropical headwater streams, China.

Low-head dams are becoming a ubiquitous feature of the landscape of headwater streams. The ecological effects of low-head dams have long been studied; however, most studies have ignored the invasion of native-invasive species commonly occurring in large streams. Based on fish data from 25 first-order streams within an important tributary of the Yangtze River, we investigated whether and how low-head dams facilitate the invasion of native-invasive fish to headwater streams in regions where native fish species are completely dominant. We found that the ratio of native-invasive species (Ratio) was significantly higher in impoundments than in free-flowing segments, suggesting that low-head dams facilitate the invasion of native-invasive fish. We demonstrated that the niche and dispersal processes affected the seasonal variation in Ratio differently. In addition, changes in the Ratio using abundance data were significantly related to landscape conditions and dam size in the dry season and only to landscape conditions in the wet season, suggesting that the latter greatly underestimated the blocking effect of low-head dams on fish dispersal. In conclusion, our study demonstrated that increasing anthropogenic landscape disturbances in catchments where low-head dams were located exacerbated the invasion of native-invasive species are commonly found in large streams. [ABSTRACT FROM AUTHOR]