Consumers can influence the competitive outcomes of prey species in various ways. Modern coexistence theory predicts that consumers can promote prey coexistence by preferably targeting a competitively superior one, thereby reducing fitness differences. However, previous studies yielded mixed conclusions. In this study, we tested the hypothesis that a parasitic annual plant, Cuscuta campestris, facilitates the coexistence of two common annual plants. We performed field surveys and parasitism experiments to parameterize a plant competition dynamics model. The model suggested a competition–defence tradeoff: the legume Lespedeza striata was a better competitor than the grass Setaria faberi, while it was more susceptible to the parasite. Moreover, an empirical host–parasite dynamics model, extended from the plant competition model, predicted their coexistence within broad, biologically reasonable ranges of parameters. This work provides field evidence of the coexisting–promoting role of a parasitic plant, as caused by stabilising feedback between host and parasite densities.

中文翻译：

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一种寄生植物促进两种一年生植物共存


消费者可以通过多种方式影响猎物物种的竞争结果。现代共存理论预测，消费者可以通过优先针对竞争优势的猎物来促进猎物共存，从而减少适应性差异。然而，以前的研究得出了不同的结论。在这项研究中，我们检验了寄生一年生植物 Cuscuta campestris 促进两种常见一年生植物共存的假设。我们进行了田间调查和寄生实验，以参数化植物竞争动力学模型。该模型提出了一种竞争-防御权衡：豆科植物 Lespedeza striata 是比草 Setaria faberi 更好的竞争对手，而它更容易受到寄生虫的影响。此外，从植物竞争模型扩展而来的经验宿主-寄生虫动力学模型预测了它们在广泛的、生物学上合理的参数范围内的共存。这项工作为寄生植物的共存促进作用提供了现场证据，这是由稳定宿主和寄生虫密度之间的反馈引起的。