eDNA reveals the impact of non-native fishes on native amphibians in mountain lakes within the global biodiversity hotspot, the Mountains of Southwest China

Alpine lakes are naturally fish-poor ecosystems that have received numerous non-native fish introductions globally over the past decades. Studies focusing on alien fish, primarily conducted in America and Europe, have shown significantly negative effects on aquatic organisms, particularly amphibians, which are vulnerable to changes in their aquatic environments. However, few studies are available from Asia, particularly in plateau lake ecosystems. In southwest China, fishes have been extensively introduced through translocation from low-elevation areas to alpine lakes within the same administrative region for religious release, tourism, and aquaculture purposes. Unfortunately, their impacts on amphibians remain largely unclear. In this study, we used environmental DNA technology to obtain a dataset of fish and amphibian species composition and abundance from 63 sampling locations in southwest China surveyed between 2022 and 2023. We examined the effects of these introductions on amphibian richness and occurrence using generalized linear models, and quantified the species co-occurrence using probabilistic species co-occurrence analysis. Next, we compared the similarity of amphibian community composition between habitats with introduced fish and fish-free habitats using the Raup-Crick index and non-metric multidimensional scaling analysis, and determined the mechanism of amphibian community assembly through modified stochasticity ratio analysis. Finally, and most importantly, we verified the co-occurrence pattern between introduced fishes and native amphibians through ex-situ experiments. Our results showed that non-native fishes mainly occur in lentic habitat, with translocated fishes comprising a significant proportion. Amphibian richness and occurrence negatively correlated with fish richness. The translocated Carassius auratus preys on Baoxing treefrog (Rhacophorus dugritei) tadpoles, significantly reducing their co-occurrence. Amphibian community composition differed between habitats, introduced fish increased amphibian community similarity and led to the dominance of stochastic processes in community assembly. Controlling introduced fish in alpine lakes is necessary to protect amphibians in the high-elevation mountains of southwest China and similar ecosystems globally.