Two herbivorous species that share a single plant can interact indirectly with one another, even without direct interaction. One type of indirect interaction is exploitative resource competition, which results from a reduction in plant biomass; another type is that caused by changes in plant traits. These are referred to as indirect effects, mediated, respectively, by biomass and plant traits. The two indirect effect types often occur simultaneously, and they are difficult to partition. To investigate the roles of the two indirect effects on both herbivores, a dynamic one-plant, two-herbivore system model was analyzed assuming the spatiotemporal co-occurrence of the herbivores and the plants’ non-specific induced defenses. Our analysis revealed that the densities of coexisting competitively superior and subordinate herbivores were regulated by negative indirect effects mediated by plant biomass and defense, respectively. This indicates that indirect effects mediated by plant biomass and plant traits can be important regulators of herbivore population size in equilibrium with herbivore coexistence. Our results could be generally applicable to plant–herbivore interactions with non-specific plant defense that is induced through both intra- and transgenerational responses.

共享一棵植物的两个草食物种可以相互间接相互作用，即使没有直接相互作用也是如此。一种间接相互作用是利用性资源竞争，这是由于植物生物量减少而引起的。另一种类型是由植物性状的变化引起的。这些分别称为间接影响，分别由生物量和植物性状介导。两种间接效应类型通常同时发生，并且很难划分。为了研究两种间接作用对两种草食动物的作用，假设草食动物的时空共存和植物的非特异性诱导防御，分析了一个动态的一植物两草食动物系统模型。我们的分析表明，竞争性上等和下等草食动物共存的密度分别受植物生物量和防御介导的负间接影响的调节。这表明由植物生物量和植物性状介导的间接作用可能是草食动物种群规模与草食动物共存平衡的重要调节剂。我们的结果通常适用于通过代内和跨代反应诱导的具有非特异性植物防御的植物-草食动物相互作用。