1. According to metacommunity theories, the structure of natural communities is the result of both environmental filtering and spatial processes, with their relative importance depending on factors including local habitat characteristics, functional features of organisms, and the spatial scale considered. However, few studies have explored environmental and spatial processes in riverine systems at local scales, explicitly incorporating spatial coordinates into multi-taxa distribution models. To address this gap, we conducted a small-scale study to discriminate between abiotic and biotic factors affecting the distribution of aquatic macroin-vertebrates, applying metacommunity concepts. 2. We studied a mountain section in each of three perennial streams within the Po River Basin (northern Italy). We sampled macroinvertebrates both in summer and winter, using specific in situ 50-point random sampling grids. Environmental factors , including benthic organic matter (BOM), flow velocity, water depth, and sub-strate were recorded together with spatial coordinates for each sampling point. The relationships between community metrics (taxon richness, abundance, bio-mass, biomass-abundance ratio, and functional feeding groups) and explanatory variables (environmental and spatial) were assessed using generalised additive models. The influence of the explanatory variables on community structure was analysed with joint species distribution models. 3. Environmental variables-primarily BOM-were the main drivers affecting community metrics, whereas the effects of spatial variables varied among metrics, streams, and seasons. During summer, community structure was strongly affected by BOM and spatial position within the riverbed, the latter probably being a proxy for mass effects mediated by biotic and stochastic processes. In contrast, community structure was mainly shaped by hydraulic variables in winter. 4. Using macroinvertebrate communities as a model group, our results demonstrate that metacommunity concepts can explain small-scale variability in community structure. We found that both environmental filtering and biotic processes shape local communities, with the strength of these drivers depending on the season. These insights provide baseline knowledge that informs our understanding of ecological responses to environmental variability in contexts including restoration ecology, habitat suitability modelling, and biomonitoring.

中文翻译：

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高清群落：空间和环境因素影响水生无脊椎动物的微观分布

1. 根据元群落理论，自然群落结构是环境过滤和空间过程共同作用的结果，其相对重要性取决于当地栖息地特征、生物功能特征和考虑的空间尺度等因素。然而，很少有研究在局部尺度上探索河流系统中的环境和空间过程，将空间坐标明确地纳入多分类群分布模型。为了解决这一差距，我们进行了一项小规模研究，应用元群落概念来区分影响水生大型脊椎动物分布的非生物和生物因素。2. 我们研究了波河流域（意大利北部）内三个常年溪流中的每一个的山地部分。我们在夏季和冬季都对大型无脊椎动物进行了采样，使用特定的原位 50 点随机采样网格。环境因素，包括底栖有机物 (BOM)、流速、水深和底质，与每个采样点的空间坐标一起记录。使用广义加性模型评估群落指标（分类群丰富度、丰度、生物量、生物量-丰度比和功能性饲养组）与解释变量（环境和空间）之间的关系。用联合物种分布模型分析解释变量对群落结构的影响。3. 环境变量——主要是 BOM——是影响社区指标的主要驱动因素，而空间变量的影响因指标、河流和季节而异。在夏季，群落结构受 BOM 和河床空间位置的强烈影响，后者可能是生物和随机过程介导的质量效应的代表。相比之下，群落结构主要受冬季水力变量的影响。4. 使用大型无脊椎动物群落作为模型组，我们的结果表明元群落概念可以解释群落结构的小规模变异。我们发现环境过滤和生物过程都会塑造当地社区，这些驱动因素的强度取决于季节。这些见解提供了基线知识，有助于我们了解环境变化的生态响应，包括恢复生态学、栖息地适宜性建模和生物监测。