Predator and prey α-diversities are often positively associated; yet, understandings of the underlying mechanisms require manipulative experiments and thus remain unclear. We attempt to address this issue by deciphering how α-diversity of predator and prey influences each other’s community assembly processes, which subsequently determine their α-diversity. The occurrence of assembly processes was indicated by the mean pairwise taxonomic index within a community (αMPTI), assuming assembly processes left traceable imprints on species’ phylogeny. Specifically, αMPTI quantifies deviations of observed phylogenetic distances from that of random, so that it can be used to hint at the occurrence of non-random/deterministic assembly processes. Larger αMPTI of a community implies the occurrence of weaker homogenizing deterministic assembly processes, which suggests that this community might be comprised of less similar species and thus has higher α-diversity. We hypothesize that higher predator and prey α-diversity would be positively associated with each other’s αMPTI, which would then be positively associated with their α-diversity. To test the hypothesis, we calculated Shannon diversity and αMPTI for heterotrophic nanoflagellates (HNF; predator) and bacteria (prey) communities in the East China Sea. The HNF Shannon diversity was found to be positively associated with αMPTI of bacteria, which was then positively associated with bacterial Shannon diversity. In contrast, bacterial Shannon diversity did not correlate with HNF’s αMPTI. We argue that top-down control is one of the explanations to the positive α-diversity association among trophic levels in microbes of the East China Sea.

中文翻译：

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群落组装过程作为海洋微生物中捕食者与猎物多样性关系的机制解释

捕食者和猎物的α多样性通常是正相关的。然而，对基本机制的理解需要进行操纵性实验，因此仍不清楚。我们试图通过破译掠食者和猎物的α多样性如何影响彼此的社区组装过程来解决这个问题，而后者随后决定了它们的α多样性。假设组装过程在物种的系统发育上留下可追踪的印记，则通过群落内的平均成对分类指数（αMPTI）指示组装过程的发生。具体来说，αMPTI量化了观察到的系统发生距离与随机发生的系统发生距离之间的偏差，因此可以用来暗示非随机/确定性组装过程的发生。社区中较大的αMPTI意味着较弱的均质化确定性装配过程，这表明该群落可能由较少的相似物种组成，因此具有较高的α多样性。我们假设更高的捕食者和猎物的α多样性将与彼此的αMPTI正相关，然后它们的α多样性将呈正相关。为了检验该假设，我们计算了东海异养纳米鞭毛虫（HNF；捕食者）和细菌（猎物）群落的香农多样性和αMPTI。发现HNF香农多样性与细菌的αMPTI正相关，然后与细菌香农多样性正相关。相反，细菌香农多样性与HNF的αMPTI不相关。我们认为自上而下的控制是东海微生物营养级之间正α-多样性联系正向的解释之一。