Data from: Spatial averaging and disturbance lead to high productivity in aquatic metacommunities

Dispersal in heterogeneous ecosystems, such as coastal metacommunities, is a major driver of diversity and productivity. According to theory, both species richness and spatial averaging shape a unimodal relationship of productivity with dispersal. We experimentally tested the hypothesis that disturbances acting on local patches would buffer the loss of productivity at high dispersal by preventing synchronized species oscillations. To simulate these disturbances, our experimental assemblages involved species that self-organized in isolation under three inflow pulsing frequencies, where hydraulic displacement and nutrient loading affected assemblage diversity and composition. At steady-state, the emerging isolated assemblages were connected at three levels of dispersal creating three metacommunities of different connectivity. Consistent with theory, as dispersal increased, species richness in the metacommunity declined; productivity however remained high. This occurred because the most productive species in our study (which dominated the isolated patch of intermediate inflow pulsing frequency) dominated all three patches (low, intermediate and high inflow pulsing frequencies) after dispersal commenced in our metacommunities. This experimental result provides empirical support for the mechanism of spatial averaging. Furthermore, disturbances, in the form of localized pulsed inflows, prevented population oscillation synchrony caused by homogenization. Overall, our observations suggest that localized environmental fluctuations and the identity of species seem to be more influential than dispersal in shaping the diversity and composition of phytoplankton assemblages and stabilizing productivity.

异质生态系统（如海岸集合群落（metacommunity））中的物种扩散，是维持群落多样性与生产力的核心驱动因素之一。理论研究表明，物种丰富度与空间平均效应共同塑造了生产力随扩散强度变化的单峰关系。本研究通过实验验证了如下假说：作用于局部生境斑块的干扰可通过抑制物种振荡同步化，缓解高扩散强度下的生产力损失。为模拟此类干扰，本实验的群落组合选用了在三种流入脉冲频率下孤立自组织形成的物种，在此条件下，水力扰动与养分负荷会调控群落的多样性与组成结构。待新形成的孤立群落组合达到稳态后，我们设置三个扩散强度梯度将其连通，构建出三种连通度各异的集合群落。与理论预测一致，随着扩散强度提升，集合群落内的物种丰富度逐渐下降，但生产力却始终维持在较高水平。该现象的成因在于：本研究中生产力最高的物种（在中等流入脉冲频率的孤立生境中占据优势）在集合群落启动扩散后，主导了低、中、高三种流入脉冲频率下的所有生境斑块。本实验结果为空间平均效应机制提供了实证支撑。此外，以局域脉冲式流入为形式的干扰，可阻止群落均质化引发的种群振荡同步化现象。综合来看，本研究结果表明，在调控浮游植物群落组合的多样性与组成结构、稳定群落生产力方面，局域环境波动与物种身份相较于扩散强度具有更为显著的影响。