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.在实验研究中，本地物种多样性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，该关系则呈现出多样的表现形式。我们提出假说：随机物种定殖（stochastic species colonization）仅适用于自然群落，而不适用于通常通过同步引入物种构建的实验群落，其可通过引发优先效应（priority effects），导致多样性-入侵关系呈非负相关。为验证该假说，我们在噬细菌原生生物物种的依次组装群落中，对本地物种多样性与定殖历史进行了操控处理。研究结果显示，尽管组装历史对入侵物种种群丰度存在显著影响，但入侵物种种群丰度仍随本地物种多样性的提升而下降。该结果主要由两方面因素驱动：一是与抗入侵物种的主导作用相关的正选择效应（positive selection effects）——该抗入侵物种与入侵物种的资源利用模式最为相似；二是在本地群落中观测到的整体较弱的优先效应。然而，提升物种多样性可显著增强优先效应，这为“更大的物种库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，将有助于理解不同自然群落中多样性-入侵关系的差异。