Most organisms are defended against others, and defenses such as secondary metabolites in plants vary across species, individuals, and subindividual organs. Plant leaves show an impressive variability in quantitative defense levels, even within the same individual. Such variation might mirror physiological constraints or represent an evolved trait. One important hypothesis for the prevalence of defense variability is that it reduces herbivory due to non-linear averaging (Jensen’s inequality). In this study, we explore the conditions under which this hypothesis is valid and how it depends on the degree of specialization of the herbivores. We thus distinguish between generalists, non-sequestering specialists, and sequestering specialists that are able to convert consumed plant defense into own defense against predators. We propose a plant-herbivore model that takes into account herbivore preference, predation pressure on the herbivores, and the three herbivore specialization strategies we consider. Our computer simulations reveal that defense level variability reduces herbivory by all three populations when nutrient concentration is strongly correlated with defense level. If the nutrient concentration is the same in all leaves, the plant benefits from high defense level variability only when the herbivores are specialists that show a considerable degree of preference for leaves on which they perform best.

中文翻译：

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植物防御水平变异对专业和通用食草动物的影响

大多数生物都可以抵御其他生物，而植物中的次生代谢物等防御则因物种，个体和亚个体器官而异。植物叶片即使在同一个体内，在定量防御水平上也表现出令人印象深刻的可变性。这种变化可能反映了生理限制或代表了进化的特征。防御可变性盛行的一个重要假设是，由于非线性平均（Jensen不等式），它减少了草食动物。在这项研究中，我们探索了该假设有效的条件以及它如何取决于草食动物的专业化程度。因此，我们区分了通才专家，非定居专家和隔离专家，这些专家能够将消耗的植物防御转换为针对捕食者的防御。我们提出了一种植物-草食动物模型，该模型考虑了草食动物的偏好，食草动物的捕食压力以及我们考虑的三种食草动物专业化策略。我们的计算机模拟表明，当营养物浓度与防御水平高度相关时，防御水平的可变性会降低所有三个种群的食草性。如果所有叶片中的养分浓度相同，则只有当食草动物是表现出对它们表现最佳的叶片的相当程度的偏爱的专家时，植物才能从高防御水平的变异中受益。我们的计算机模拟表明，当营养物浓度与防御水平高度相关时，防御水平的可变性会降低所有三个种群的食草性。如果所有叶片中的养分浓度相同，则只有当食草动物是表现出对它们表现最佳的叶片的相当程度的偏爱的专家时，植物才能从高防御水平变异中受益。我们的计算机模拟表明，当营养物浓度与防御水平高度相关时，防御水平的可变性会降低所有三个种群的食草性。如果所有叶片中的养分浓度相同，则只有当食草动物是表现出对它们表现最佳的叶片的相当程度的偏爱的专家时，植物才能从高防御水平的变异中受益。