Abstract Headwater streams are interesting ecological systems for studies of metacommunities given their high degrees of isolation, unidirectionality of water flow and hierarchical organization in the drainage network. In addition, for passively dispersing aquatic organisms (e.g. planktonic diatoms), connectivity between sites is unidirectional, which implies a higher isolation of headwaters, leading to a greater dispersal limitation between streams. The aim of this study was to evaluate the relative importance of local environmental (i.e., physicochemical variables) and spatial (i.e., distance between sites) components to the planktonic diatom community in 28 headwater streams of the Cerrado, central region of Brazil. Due the fact that each sampling point was located in a different headwater stream, we expected that spatial components (a proxy for diatom dispersal) were more important than local environmental conditions to the structure of the diatom metacommunity. We found 51 morphospecies of diatoms (Bacillariophyceae). The community composition of diatoms showed strong spatial variation, which was also indicated by high beta diversity (mainly contributed by the turnover component). The variation in diatom community composition, species richness, total density, and Local Contribution to Beta Diversity (LCBD) of headwaters streams was explained solely by spatial factors. Based on these results, we inferred that due to dispersal limitation, the diatom communities of these headwaters tend to show distinct species composition, with high species turnover among the local communities. We highlight the importance of headwater streams as reservoirs of biodiversity for a riverine diatom metacommunity.

中文翻译：

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空间过程决定了源头溪流的浮游硅藻元群落结构

摘要 源头流是研究元群落的有趣生态系统，因为它们高度孤立、水流单向和排水网络中的分层组织。此外，对于被动扩散的水生生物（例如浮游硅藻），站点之间的连通性是单向的，这意味着源头的隔离度更高，导致溪流之间的扩散限制更大。本研究的目的是评估当地环境（即物理化学变量）和空间（即站点之间的距离）组件对巴西中部地区塞拉多 28 条上游河流中浮游硅藻群落的相对重要性。由于每个采样点位于不同的源头水流中，我们预计空间成分（代表硅藻扩散）比当地环境条件对硅藻群落结构更重要。我们发现了 51 种硅藻 (Bacillariophyceae)。硅藻群落组成表现出强烈的空间变异，这也表现为高β多样性（主要由周转分量贡献）。硅藻群落组成、物种丰富度、总密度和上游河流对 Beta 多样性 (LCBD) 的局部贡献的变化仅由空间因素解释。基于这些结果，我们推断由于扩散限制，这些源头的硅藻群落往往表现出不同的物种组成，当地群落之间的物种周转率很高。