Data from: Predators regulate prey species sorting and spatial distribution in microbial landscapes

1. The role of predation in determining the metacommunity assembly model of prey communities is understudied relative to that of interspecific competition among prey. Previous work on metacommunity dynamics of competing species has shown that sorting by habitat patch type and spatial patterning can be affected by disturbances.
2. Microcosms offer a useful model system to test the effect of multi-trophic interactions and disturbance on metacommunity dynamics. Here, we investigated the potential role of predators in enhancing or disrupting sorting and spatial pattern among prey in experimental landscapes.
3. We exposed multi-trophic protist microcosm landscapes with one predator, two competing prey, two patch resource types, and localized dispersal to three disturbance regimes (none, low, and high). Then, we used variation partitioning and spatial clustering analysis to analyze the results.
4. In contrast with previous experiments that did not manipulate predators, we found that patch type did not structure prey communities very well. Instead, we found that it was the distribution of the predator that most strongly predicted the composition of the prey community.
5. The predator impacted species sorting by 1) preferentially consuming one prey, thereby acting as a strong local environmental driver, and by 2) indirectly magnifying the impact of patch food resources on the less preferred prey. The predator also enhanced spatial signal in the prey community because of its limited dispersal. Our results indicate that predators can strongly influence prey species sorting and spatial patterning in metacommunities in ways that would otherwise be attributed to stochastic effects, such as dispersal limitation or demographic drift. Therefore, whenever possible, predators should be explicitly included as separate explanatory factors in variation partitioning analyses.

1. 相较于猎物种群间的种间竞争，捕食作用在决定猎物种集合群落（metacommunity）组装模式中的作用尚未得到充分研究。此前针对竞争物种的集合群落动态的已有研究表明，生境斑块类型筛选及空间格局会受到干扰作用的影响。
2. 微宇宙（microcosm）实验系统为探究多营养级相互作用与干扰对集合群落动态的影响提供了理想模型。本研究以实验景观为对象，探究了捕食者在增强或干扰猎物种筛选与空间格局过程中的潜在作用。
3. 我们构建包含1种捕食者、2种竞争猎物、2种斑块资源类型以及局域扩散的多营养级原生生物微宇宙实验景观，并设置三种干扰制度（无干扰、低干扰、高干扰）开展实验处理。随后采用变异分割（variation partitioning）与空间聚类分析方法对实验结果进行解析。
4. 与未开展捕食者操控实验的既往研究结果不同，本研究发现生境斑块类型无法有效塑造猎物种群落结构。与之相反，捕食者的空间分布才是预测猎物种群落组成的最强解释因子。
5. 捕食者通过两条途径影响物种筛选：其一，优先取食某一猎物种群，从而成为强有力的局域环境驱动因子；其二，间接放大了斑块食物资源对低偏好猎物的影响效应。此外，由于自身扩散受限，捕食者还增强了猎物种群落的空间信号强度。本研究结果表明，捕食者可强烈影响集合群落中的猎物种筛选与空间格局，其相关影响效应原本会被归因于扩散限制、种群统计漂变等随机生态学过程。因此，在开展变异分割分析时，应尽可能将捕食者作为独立解释因子纳入分析框架。