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.

实验研究中，本地物种多样性（resident species diversity）与生物入侵（invasion）之间的关系通常呈负相关，但在针对自然群落（natural communities）的观测研究（observational studies）中，该关系呈现多种表现形式。我们提出假说：适用于自然群落、但不适用于通常通过同步物种引种构建的实验群落的物种随机定殖（stochastic species colonization），可通过引发优先效应（priority effects），使得多样性-入侵关系呈现非负性。为验证该假说，我们在依次构建的食细菌原生动物（bacterivorous protist）群落中，同时操控本地物种多样性与定殖历史两个变量。研究结果显示：尽管群落构建历史（assembly history）对入侵者多度（invader abundance）存在显著影响，但入侵者多度随本地物种多样性的升高而降低。该结果主要由两类效应驱动：一是与抗入侵物种（invasion-resistant species）主导作用相关的正选择效应（positive selection effects）——该抗入侵物种与入侵者的资源利用模式（resource use pattern）最为相似；二是观测到的本地群落优先效应整体偏弱。然而，本地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（alternative community states）形成”这一观点提供了首个实验支撑。我们认为，阐明调控优先效应强度的核心机制，或有助于理解不同自然群落间多样性-入侵关系的差异。