Data from: Species diversity, invasion, and alternative community states in sequentially assembled communities

The relationship between resident species diversity and invasion is generally negative in experimental studies, but takes various forms in observational studies of natural communities. We hypothesized that stochastic species colonization, which applies to natural communities but not experimental communities generally assembled through simultaneous species introduction, may lead to non-negative diversity-invasion relationships via incurring priority effects. To test this hypothesis, we manipulated both resident species diversity and colonization history in sequentially assembled communities of bacterivorous protist species. We found that despite a significant effect of assembly history on invader abundance, invader abundance declined with diversity. This result was largely driven by positive selection effects associated with the dominant influence of an invasion-resistant species, which shared the most similar resource use pattern with the invader, and by the overall weak priority effects observed for the resident communities. Increasing species diversity, however, significantly strengthened priority effects, providing the first experimental support for the idea that larger species pools promote alternative community states. We suggest that elucidating mechanisms regulating the strength of priority effects may help understand variation in diversity-invasion relationships among natural communities.现有实验研究普遍表明，本地物种多样性（resident species diversity）与生物入侵之间的关系通常呈负相关，但在自然群落的观测研究中，该关系则呈现多种不同表现形式。我们提出假说：随机物种定殖（stochastic species colonization）适用于自然群落，但不适用于通常通过同步引入物种构建的实验群落，该过程可通过引发优先效应（priority effects），使得多样性-入侵关系呈现非负相关的特征。为验证这一假说，我们在逐次组装的食菌原生动物物种群落中，对本地物种多样性与定殖历史进行了操控实验。研究结果显示，尽管组装历史对入侵者丰度存在显著影响，但入侵者丰度仍随多样性升高而下降。这一结果主要由两类因素驱动：一是与抗入侵物种相关的正向选择效应（selection effects）——该物种与入侵者的资源利用模式最为相似；二是观测到的本地群落整体较弱的优先效应。然而，物种多样性的提升显著增强了优先效应，这为"更大的物种库（species pools）可促进替代群落状态的形成"这一观点提供了首个实验证据。我们认为，阐明调控优先效应强度的机制，或有助于理解不同自然群落间多样性-入侵关系的差异。