Extreme drying can dramatically shift abiotic characteristics of streams and species respond differently as conditions change. We modified a conceptual model describing responses of aquatic invertebrate assemblages to stream drying to facilitate predictions of fish assemblage shifts in which thresholds of physiochemical gradients lead to punctuated losses of fish diversity as stream connectivity diminishes. We tested the applicability of this model during a record-breaking drought that reduced a perennial reach of a headwater prairie stream to a series of 12 isolated pools with variable levels of hyporheic connectivity that was associated with pool volume. We tracked fish assemblage structure in pools over seven weeks and measured abiotic conditions. Inter-specific differences in drought resistance traits were tested in the lab (i.e., thermal and hypoxia tolerance) for common species experiencing drought conditions. Species richness declined rapidly with pool volume associated with hyporheic connectivity. Abundance of the most common species prior to drought, Chrosomus erythrogaster (southern redbelly dace) declined 95% and was extirpated from five pools during drought due to its low thermal tolerance. Despite being the least tolerant to hypoxia, Campostoma anomalum (central stoneroller) populations persisted in most pools. The remaining pools became dominated by a non-native extremophile fish, Gambusia affinis (western mosquitofish) and abundances of less resistant native species declined. Our study demonstrates that richness in drying pools is driven by factors associated with pool volume, and assemblage composition shifts from dominance by native species adapted to variable hydrological conditions to non-native species able to resist increasing temperatures and hypoxia. Sudden species loss associated with reduced stream connectivity can shift abundance patterns of prairie stream fish communities with potentially lagged effects on population and community dynamics.

中文翻译：

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无处可游：严重干旱期间草原溪流鱼类在孤立池中的种间反应

极端干燥会显着改变河流的非生物特征，物种随着条件的变化做出不同的反应。我们修改了一个概念模型，该模型描述了水生无脊椎动物组合对河流干燥的反应，以促进鱼类组合变化的预测，其中物理化学梯度的阈值导致鱼类多样性的间断性损失，因为河流连通性减弱。我们在破纪录的干旱期间测试了该模型的适用性，该干旱将源头草原溪流的常年范围减少到一系列 12 个孤立的水池，这些水池具有与水池体积相关的可变水平的低流连通性。我们在七周内跟踪了水池中的鱼类组合结构并测量了非生物条件。在实验室中测试了抗旱性状的种间差异（即，热和缺氧耐受性）适用于经历干旱条件的常见物种。物种丰富度随着与低流连通性相关的池体积而迅速下降。Chrosomus erythrogaster（南红腹鲱）是干旱前最常见的物种，数量减少了 95%，由于其耐热性低，在干旱期间从五个水池中灭绝。尽管对缺氧的耐受性最差，Campostoma anomalum (central stoneroller) 种群在大多数水池中仍然存在。剩余的水池被一种非本地嗜极鱼类 Gambusia affinis（西方蚊鱼）所支配，而抵抗力较差的本地物种的数量则有所下降。我们的研究表明，干燥池的丰富度是由与池体积相关的因素驱动的，和组合组成从适应可变水文条件的本地物种的主导地位转变为能够抵抗不断升高的温度和缺氧的非本地物种。与河流连通性降低相关的突然物种丧失会改变草原河流鱼类群落的丰度模式，对种群和群落动态产生潜在的滞后影响。