Seventy-five years of biodiversity decline of fish assemblages in Chinese isolated plateau lakes: widespread introductions and extirpations of narrow endemics lead to regional loss of dissimilarity

Aim Introductions of exotic species have globally modified the structure and function of native assemblages and are recognized as one of the major threats to biodiversity. The current patterns, processes and consequences of invasion have been intensively studied globally, but studies reporting the long-term dynamics of invasions over large areas are rare. Here, we measured how the temporal changes in fish assemblage composition in a Chinese highland isolated-lake landscape drive taxonomic dissimilarity and its turnover component over three successive time periods spanning the last 75 years. Location Yun-Gui Plateau, 15 isolated lakes. Methods The Sorensen and Simpson indices were used to quantify changes in taxonomic dissimilarity and its turnover component over 1940-2015. Results We report a decline of taxonomic dissimilarity between lakes through time, mainly due to a decrease in species turnover. Such a homogenization process was due to the combined effects of the invasion of the same non-native species in most lakes and of extirpation of narrow endemic species. The strong decline in species dissimilarity and turnover was triggered by a high historical level of dissimilarity among assemblages. At a regional scale, the combined effect of introductions and extirpations modified the distance decay of taxonomic similarity between lakes. Surprisingly, this beta-diversity gradient is currently no longer supported by biogeographic and evolutionary processes, but by the human-mediated introduction of distinct exotic species in some lakes. Moreover, an extinction debt process was evident as extirpations sometimes occurred many years after the introduction of non-native species. Main conclusions Our study highlights that high historical differentiation of fishes in isolated lakes has turned to homogenization with dramatic loss of endemic species due to intensive introductions. This provides a striking example of human domination over an extended lake landscape and its associated irreparable biodiversity damages on isolated systems historically dominated by narrow endemic species.