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 or fish-free ecosystems that have received numerous non-native fish introductions globally in recent decades. Studies have demonstrated that alien fish have significant negative impacts on aquatic organisms, particularly amphibians, which are highly susceptible to habitat alterations. However, studies from Asia remain scarce, particularly in plateau lake ecosystems. In southwest China, fish have been extensively introduced through alien and intra-regional translocation for purposes including religious release, tourism, and aquaculture. In this study, we used environmental DNA techniques to survey fish and amphibian species composition and abundance at 63 sampling locations across southwest China between 2022 and 2023. We examined the effects of fish introductions on amphibian richness and occurrence using generalized linear models, and further evaluated the impact magnitude of fish from different sources. We then quantified the species co-occurrence using probabilistic species co-occurrence analysis. Next, we evaluated the impact of fish richness from different sources on community composition using non-metric multidimensional scaling, and assessed community similarity and assembly mechanism through the Raup-Crick index and modified stochasticity ratio. Ultimately, we explored the predation behavior of selected pairs of translocated fish and native amphibian to verify the cause of negative co-occurrence. Our results showed that non-native fish predominantly inhabit lentic habitats, with translocated species comprising a substantial proportion. Amphibian richness and occurrence were negatively correlated with fish richness. Introduced fish increased amphibian community similarity and shifted community assembly toward stochastic dominance. Translocated <i>Carassius auratus</i> exhibited strong predation on <i>Rhacophorus dugritei</i> tadpoles, significantly reducing its occurrence. These impacts were largely driven by intra-regional fish translocation. Our findings highlight the critical need to consider intra-regional fish movements in conservation strategies. This study provides key insights for managing introduced fish populations and protecting threatened and endemic amphibians in alpine lake ecosystems of southwest China and similar highland regions worldwide.

高山湖泊是自然状态下鱼类匮乏或无鱼的生态系统，近几十年来全球范围内已被大量引入非本土鱼类。已有研究表明，外来鱼类对水生生物具有显著负面影响，其中对栖息地变化高度敏感的两栖类尤甚。然而，亚洲地区的相关研究仍较为匮乏，高原湖泊生态系统的相关研究更是不足。在中国西南地区，出于宗教放生、旅游观光及水产养殖等目的，通过外来物种引入和区域内鱼类转运的方式，已大量引入鱼类。本研究于2022至2023年间，利用环境DNA（environmental DNA, eDNA）技术，对中国西南地区63个采样点的鱼类及两栖类物种组成与丰度进行了调查。本研究采用广义线性模型（generalized linear models, GLMs）分析了鱼类引入对两栖类物种丰富度及出现率的影响，并进一步评估了不同来源鱼类的影响强度。随后，通过概率性物种共现分析，量化了物种间的共现模式。继而，采用非度量多维标度（non-metric multidimensional scaling, NMDS）分析了不同来源的鱼类丰富度对群落组成的影响，并通过Raup-Crick指数与修正随机性比例（modified stochasticity ratio, MSR）评估了群落相似性及组装机制。最后，通过选取转运鱼类与本土两栖类的配对组合，探究其捕食行为，以验证负共现模式的成因。研究结果显示，非本土鱼类主要栖息于静水生境，其中转运引入的物种占比可观。两栖类物种丰富度与出现率均与鱼类丰富度呈显著负相关。引入鱼类提升了两栖类群落的相似性，并使群落组装向随机性主导方向转变。转运引入的鲫（Carassius auratus）对杜氏泛树蛙（Rhacophorus dugritei）的蝌蚪展现出极强的捕食能力，显著降低了该物种的出现率。上述影响主要由区域内鱼类转运所驱动。本研究结果凸显了在保护策略中纳入区域内鱼类流动管控的必要性。本研究为中国西南地区高山湖泊生态系统及全球类似高原区域的外来鱼类种群管理，以及濒危与特有两栖类的保护提供了重要参考依据。