Specialized pathogens are thought to maintain plant community diversity; however, most ecological studies treat pathogens as a black box. Here we develop a theoretical model to test how the impact of specialized pathogens changes when plant resistance genes (R-genes) mediate susceptibility. This work synthesizes two major hypotheses: the gene-for-gene model of pathogen resistance and the Janzen-Connell hypothesis of pathogen-mediated coexistence. We examine three scenarios. First, R-genes do not affect seedling survival; in this case, pathogens promote diversity. Second, seedlings are protected from pathogens when their R-gene alleles and susceptibility differ from those of nearby conspecific adults, thereby reducing transmission. If resistance is not costly, pathogens are less able to promote diversity because populations with low R-gene diversity suffer higher mortality, putting those populations at a disadvantage and potentially causing their exclusion. R-gene diversity may also be reduced during population bottlenecks, creating a priority effect. Third, when R-genes affect survival but resistance is costly, populations can avoid extinction by losing resistance alleles, as they cease paying a cost that is unneeded. Thus, the impact pathogens can have on tree diversity depends on the mechanism of plant-pathogen interactions. Future empirical studies should examine which of these scenarios most closely reflects the real world.

中文翻译：

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抗性基因影响病原体如何维持植物的丰度和多样性。

专门病原体被认为可以维持植物群落的多样性。但是，大多数生态学研究将病原体视为黑匣子。在这里，我们建立了一个理论模型来测试当植物抗性基因（R基因）介导敏感性时专业病原体的影响如何变化。这项工作综合了两个主要假设：病原体抗性的基因对基因模型和病原体介导的共存的Janzen-Connell假设。我们研究了三种情况。首先，R基因不会影响幼苗的存活。在这种情况下，病原体会促进多样性。其次，当幼苗的R基因等位基因和易感性与附近同种成体的幼苗不同时，可以保护幼苗免受病原体的侵害，从而减少传播。如果抵抗不是很昂贵，由于低R基因多样性的种群遭受更高的死亡率，致使这些种群处于不利地位并可能导致其被排斥，病原体促进多样性的能力降低。在人口瓶颈期间，R基因多样性也可能减少，从而产生优先效应。第三，当R基因影响生存但抵抗力代价高昂时，种群可以通过失去抵抗等位基因来避免灭绝，因为他们不再支付不必要的费用。因此，病原体对树木多样性的影响取决于植物与病原体相互作用的机制。未来的实证研究应检查以下哪种情况最能真实反映现实世界。产生优先效果。第三，当R基因影响生存但抗性代价高昂时，种群可以通过失去抗性等位基因来避免灭绝，因为他们不再支付不必要的费用。因此，病原体对树木多样性的影响取决于植物与病原体相互作用的机制。未来的实证研究应检查以下哪种情况最能真实反映现实世界。产生优先效果。第三，当R基因影响生存但抵抗力代价高昂时，种群可以通过失去抵抗等位基因来避免灭绝，因为他们不再支付不必要的费用。因此，病原体对树木多样性的影响取决于植物与病原体相互作用的机制。未来的实证研究应检查以下哪种情况最能真实反映现实世界。