1. Climate change is a major threat to biodiversity. Rainfall patterns over recent decades have changed and extreme events are intensifying. These are expected to affect the hydrological dynamics and structure of forest streams in the Amazon basin, which strongly depend on the local rainfall regime, with potential consequences for local fish assemblages.
2. Here we used four repeated surveys of stream fish assemblages across 10 × 10 km area of a pristine forest reserve in central Amazonia over an 18‐year (2001–2018) period to investigate the temporal dynamics of fish taxonomic and functional composition in relation to changes in stream habitats and local climatic regime. We investigated changes in magnitude, direction, and congruence of fish assemblage trajectories over time.
3. Total annual rainfall increased over time, with stormy days (i.e. daily rainfall above 20 mm) becoming more frequent during recent decades and a concomitant change of stream substrates from litter‐dominated to free sand. The overall taxonomic and functional composition of fish assemblages changed consistently over time, with stronger differences between the first and last surveys due to alterations in relative abundances of some of the most abundant species. Functional composition moved from open water species (compressed‐bodied species with less developed fins and terminal‐oriented mouths) to species adapted to lateral pools and shallow marginal areas (species with fusiform body shape, more developed fins, and superior‐oriented mouth)
4. We provide evidence of a concerted directional change of fish assemblages associated with increased precipitation and a higher frequency of stormy days over the last 2 decades. Considering the short time interval and the subtleness of the climatic changes assessed in this study, as well as the historically assumed structural stability of Amazonian streams, these findings are surprising and indicate those stream fish assemblages may respond quickly to climate changes.

中文翻译：

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降雨的时间变化影响亚马逊河中部溪流鱼类的分类和功能组成

1. 气候变化是对生物多样性的主要威胁。近几十年来的降雨方式已经改变，极端事件正在加剧。预计这些因素将影响亚马逊流域的森林溪流的水文动力学和结构，这在很大程度上取决于当地的降雨状况，并对当地鱼类的聚集产生潜在的影响。
2. 在这里，我们使用了四次重复调查，调查了18年（2001-2018年）期间亚马逊中部原始森林保护区10×10 km区域溪流鱼类的聚集情况，调查了鱼类生物分类和功能成分与变化的时间动态关系。在河流栖息地和当地的气候环境中。我们调查了鱼类聚集轨迹的大小，方向和一致性随时间的变化。
3. 随着时间的流逝，每年的总降雨量增加，在最近的几十年中，暴风雨的日子（即每天降雨量超过20毫米）变得更加频繁，溪流底物也随之从垃圾占主导的状态变为自由沙型。鱼群的总体分类和功能组成随时间不断变化，由于某些最丰富种类的相对丰度发生了变化，第一次和最后一次调查之间的差异更大。功能成分从开放水域物种（鳍片较少而末端为嘴的紧实物种）变为适应侧池和浅边缘区域的物种（梭形体形，较发达的鳍片和上位嘴的物种）
4. 我们提供的证据表明，在过去的20年中，鱼群的方向发生了协调一致的变化，这与降雨增加和暴风雨频率增加有关。考虑到本研究评估的短时间间隔和气候变化的微妙性，以及历史上假定的亚马逊河溪流的结构稳定性，这些发现令人惊讶，表明这些溪流鱼类组合可能对气候变化做出快速反应。