Understanding and predicting the geographic distribution of taxa in hierarchical stream landscapes is a cornerstone of river ecology. A central issue is to tease apart the unique and shared effects of local and catchment predictors over species distributions. Here, we tested Hynes's influential hypothesis (1975, Baldi Memorial Lecture) that ‘In every respect, the valley rules the stream'. We predicted that if catchment features exert a major control on in-stream local conditions, the shared effect of local and catchment predictors should largely surpass their unique effects. To test this prediction, we used logistic regression models and variation partitioning to quantify the unique and shared effects of local and catchment predictors on the distribution of two hyporheic crustacean taxa (Bogidiellidae, Amphipoda and Anthuridae, Isopoda) in streams of New Caledonia. We sampled the two taxa at 228 sites. At each site, we quantified nine local predictors related to habitat area and stability, sediment metabolism and water origin, and eight catchment predictors related to geology, area, primary productivity, land use and specific discharge. When analyzed separately, the two predictor types explained the same amount of model variation in occurrence in both taxa. When analyzed jointly, the shared effects of the two predictor types explained twice as much model variation as the unique effect of each. The overriding contribution of shared effects was notably due to controls exerted by catchment area and geology on local habitat size and sediment metabolism, respectively. For both taxa, a model with only these two catchment predictors provided occurrence distribution as reliable as models containing only local predictors or both predictor types. Our findings pave the way for predicting reliably from catchment predictors alone the geographic distribution in local occurrence of taxa in difficult-to-access habitats and landscapes, such as here the hyporheic zone of tropical streams.

中文翻译：

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局部和流域预测因子对潜流生物分布的独特和共同影响：山谷是否统治河流？

了解和预测分级河流景观中分类群的地理分布是河流生态学的基石。一个核心问题是梳理局部和流域预测变量对物种分布的独特和共同影响。在这里，我们检验了海因斯的有影响力的假设（1975 年，巴尔迪纪念讲座），即“在各个方面，山谷都统治着河流”。我们预测，如果流域特征对河流局部条件施加主要控制，则局部和流域预测因子的共同效应应在很大程度上超过其独特效应。为了检验这一预测，我们使用逻辑回归模型和变异划分来量化局部和集水区预测因子对两种低流甲类动物类群（Bogidiellidae、两足类和 Anthuridae）分布的独特和共同影响。Isopoda）在新喀里多尼亚的溪流中。我们在 228 个地点对这两个分类群进行了抽样。在每个站点，我们量化了与栖息地面积和稳定性、沉积物代谢和水源相关的九个局部预测因子，以及与地质、面积、初级生产力、土地利用和特定排放量相关的八个流域预测因子。当分开分析时，这两种预测变量类型解释了两个分类群中发生的相同数量的模型变化。联合分析时，两种预测变量类型的共同效应解释的模型变异是每种预测变量的独特效应的两倍。共享效应的压倒性贡献主要是由于集水区和地质分别对当地栖息地大小和沉积物代谢施加的控制。对于两个分类群，仅包含这两个流域预测变量的模型提供的发生分布与仅包含局部预测变量或两种预测变量类型的模型一样可靠。我们的研究结果为仅从流域预测因子可靠地预测难以进入的栖息地和景观中分类群的局部发生的地理分布铺平了道路，例如这里的热带溪流的低流带。