Unraveling the determinants of herbivorous insect diversity has been a significant challenge in ecology. Despite the strong association between insect and plant species, previous studies conducted in natural systems have shown great variation in the strength of the correlation between their species richness. Such variation could be attributed to the proportion of generalist insect species (generality). However, both higher and lower generality may weaken the correlation because (a) generalist insect species are less dependent on the number of plant species, and (b) specialist insect species utilize only a proportion of the total plant species. To explore these contradictory effects, we studied plant and herbivorous insect communities in seminatural grasslands in Japan. Plant–insect interactions were evaluated in a unique way with a particular focus on the staying and herbivory behaviors of insects, which reflect their habitat use as well as host use. We found that lower generality of insect communities strengthened the correlation between species richness of plants and insects, but this was not the case when plant species that had no interaction with insect species were also considered. This was because lower generality increased the number of plant species that did not interact with insects. The results indicate that insect generality has contradictory effects on the plant–insect diversity relationship, which emphasizes the importance of distinguishing the effects to understand the variation in the relationship between plant and insect diversity in natural systems.

中文翻译：

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为什么植物和草食性昆虫的物种丰富度相互关联或不相关

揭示草食性昆虫多样性的决定因素一直是生态学上的重大挑战。尽管昆虫和植物物种之间有很强的联系，但以前在自然系统中进行的研究表明，它们的物种丰富度之间的相关强度存在很大差异。这种变化可归因于通才昆虫种类的比例（属）。但是，较高和较低的通用性都可能削弱这种相关性，因为（a）普通昆虫物种对植物物种的依赖性较小，并且（b）专门昆虫物种仅利用总植物物种的一部分。为了探讨这些矛盾的影响，我们研究了日本半天然草原上的植物和草食性昆虫群落。以一种独特的方式评估了植物与昆虫之间的相互作用，特别着重于昆虫的停留和食草行为，这些行为反映了它们的栖息地使用和寄主使用。我们发现，昆虫群落的普遍性较低，增强了植物和昆虫物种丰富度之间的相关性，但是当不考虑与昆虫物种没有相互作用的植物物种时，情况并非如此。这是因为较低的通用性增加了不与昆虫相互作用的植物物种的数量。结果表明，昆虫的普遍性对植物-昆虫多样性关系具有矛盾的影响，这强调了区分这些影响以了解自然系统中植物与昆虫多样性之间关系变化的重要性。