Understanding spatiotemporal trends on insect-plant interaction networks is essential to unveil the ecological and evolutionary processes driving herbivore specialisation. However, community studies accounting for temporal dynamics in host-plant specialisation of herbivorous insects are surprisingly scarce. Here, we investigated how seasonality affects specialisation of a temperate forest herbivore community. A substantial body of literature suggests that young plant foliage tends to be more protected by defence mechanisms effective against generalist insect herbivores than mature leaves. We thus hypothesised that herbivore specialisation would be highest in the early season, when young leaves are available, and that the degree of dietary specialisation would decline with leaf maturation. To test this hypothesis, we sampled more than 4700 folivorous caterpillars associated with 16 tree species within a 0.2 ha deciduous forest stand in eastern North America. We further examined the dietary specialisation of exposed feeders versus shelter builders (e.g. leaf rollers, leaf tiers, webbers). Contrary to our prediction, we observed a significantly less specialised herbivore fauna in the early season than in the two subsequent summer seasons. We further found that the seasonal increase in specialisation was driven by a remarkable turnover in species composition rather than by shifts in guild structure or intraspecific changes in diet breadth of the herbivores. These findings run counter to the widespread belief that young leaves are less susceptible to generalist insect herbivores. Our study underscores the need to account for temporal dynamics when contrasting herbivore specialisation among sites with pronounced seasonality.

中文翻译：

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季节性影响温带森林食草动物群落的专业化

了解昆虫-植物相互作用网络的时空趋势对于揭示推动食草动物专业化的生态和进化过程至关重要。然而，解释食草昆虫寄主植物专业化的时间动态的社区研究令人惊讶地稀少。在这里，我们调查了季节性如何影响温带森林食草动物群落的专业化。大量文献表明，与成熟的叶子相比，年轻的植物叶子更容易受到有效防御昆虫食草动物的防御机制的保护。因此，我们假设草食动物的专业化在早期的幼叶可用时最高，并且饮食专业化的程度会随着叶的成熟而下降。为了检验这个假设，我们在北美东部 0.2 公顷的落叶林中对 4700 多只与 16 种树种相关的食叶毛虫进行了采样。我们进一步检查了暴露的饲养者与庇护所建造者（例如卷叶者，叶层，韦伯）的饮食专业化。与我们的预测相反，与随后的两个夏季相比，我们在早期观察到的专门化草食动物群明显减少。我们进一步发现，专业化的季节性增加是由物种组成的显着变化驱动的，而不是由公会结构的变化或食草动物饮食宽度的种内变化驱动的。这些发现与普遍的看法背道而驰，即年轻的叶子不太容易受到昆虫食草动物的影响。