Data from: Assembly mechanisms determining high species turnover in aquatic communities over regional and continental scales

Niche and neutral processes drive community assembly and metacommunity dynamics, but their relative importance might vary with the spatial scale. The contribution of niche processes is generally expected to increase with increasing spatial extent at a higher rate than that of neutral processes. However, the extent to what community composition is limited by dispersal (usually considered a neutral process) over increasing spatial scales might depend on the dispersal capacity of composing species. To investigate the mechanisms underlying the distribution and diversity of species known to have great powers of dispersal (hundreds of kilometres), we analysed the relative importance of niche processes and dispersal limitation in determining beta-diversity patterns of aquatic plants and cladocerans over regional (up to 300 km) and continental (up to 3,300 km) scales. Both taxonomic groups were surveyed in five different European regions and presented extremely high levels of beta-diversity, both within and among regions. High beta-diversity was primarily explained by species replacement (turnover) rather than differences in species richness (i.e. nestedness). Abiotic and biotic variables were the main drivers of community composition. Within some regions, small-scale connectivity and the spatial configuration of sampled communities explained a significant, though smaller, fraction of compositional variation, particularly for aquatic plants. At continental scale (among regions), a significant fraction of compositional variation was explained by a combination of spatial effects (exclusive contribution of regions) and regionally-structured environmental variables. Our results suggest that, although dispersal limitation might affect species composition in some regions, aquatic plant and cladoceran communities are not generally limited by dispersal at the regional scale (up to 300 km). Species sorting mediated by environmental variation might explain the high species turnover of aquatic plants and cladocerans at regional scale, while biogeographic processes enhanced by dispersal limitation among regions might determine the composition of regional biotas.

生态位过程（niche processes）与中性过程（neutral processes）驱动群落构建（community assembly）与集合群落动态（metacommunity dynamics），但二者的相对重要性可能随空间尺度（spatial scale）发生变化。一般而言，生态位过程的贡献随空间范围（spatial extent）扩大的增速通常高于中性过程。然而，在空间尺度扩大的过程中，群落组成受扩散（通常被视为中性过程）限制的程度，可能取决于所研究物种的扩散能力。为探究具备强扩散能力（扩散距离可达数百公里）的物种其分布与多样性背后的机制，我们分析了生态位过程与扩散限制（dispersal limitation）在决定水生植物（aquatic plants）和枝角类（cladocerans）的β多样性（beta-diversity）格局中的相对重要性，研究覆盖区域尺度（最大跨度300 km）与大陆尺度（最大跨度3300 km）两个梯度。两类生物类群均在5个不同的欧洲区域开展了调查，且区域内与区域间均表现出极高的β多样性水平。高β多样性主要由物种替换（周转，turnover）而非物种丰富度（species richness）差异（即嵌套性，nestedness）所主导。非生物变量（abiotic variables）与生物变量（biotic variables）是群落组成的核心驱动因子。在部分区域内，小尺度连通性与采样群落的空间构型（spatial configuration）能够解释一定比例的组成变异，尽管该占比相对较低，对水生植物而言尤为显著。在大陆尺度（区域间），空间效应（区域的专属贡献）与区域结构化环境变量的组合能够解释显著的组成变异。我们的研究结果显示，尽管扩散限制可能在部分区域对物种组成产生影响，但水生植物与枝角类群落通常不会在区域尺度（跨度最高300 km）受到扩散限制。由环境变异介导的物种分选能够解释区域尺度下水生植物和枝角类的高物种周转，而区域间由扩散限制强化的生物地理过程（biogeographic processes）或可决定区域生物群的组成。