Data from: Leaf drop affects herbivory in oaks

Leaf phenology is important to herbivores, but the timing and extent of leaf drop has not played an important role in our understanding of herbivore interactions with deciduous plants. Using phylogenetic general least squares regression, we compared the phenology of leaves of 55 oak species in a common garden with the abundance of leaf miners on those trees. Mine abundance was highest on trees with an intermediate leaf retention index, i.e. trees that lost most, but not all, of their leaves for 2–3 months. The leaves of more evergreen species were more heavily sclerotized, and sclerotized leaves accumulated fewer mines in the summer. Leaves of more deciduous species also accumulated fewer mines in the summer, and this was consistent with the idea that trees reduce overwintering herbivores by shedding leaves. Trees with a later leaf set and slower leaf maturation accumulated fewer herbivores. We propose that both leaf drop and early leaf phenology strongly affect herbivore abundance and select for differences in plant defense. Leaf drop may allow trees to dispose of their herbivores so that the herbivores must recolonize in spring, but trees with the longest leaf retention also have the greatest direct defenses against herbivores.

叶片物候对植食性动物具有重要意义，但落叶的时序与脱落程度，在当前学界理解植食性动物与落叶植物的互作关系中，并未得到应有的重视。本研究采用系统发育广义最小二乘回归（phylogenetic general least squares regression）方法，对比了同质园中55种栎树的叶片物候，及其寄主树上潜叶昆虫（leaf miners）的种群丰度。研究结果显示：叶片保留指数处于中等水平的树木——即落叶时长为2~3个月、脱落大部分但未完全脱落叶片的植株——其潜叶昆虫丰度最高。常绿性越强的树种，叶片硬化程度越高，而硬化叶片在夏季的潜叶昆虫虫量更少。落叶性越强的树种，夏季的潜叶昆虫虫量同样更低，该结果与“树木通过脱落叶片以清除越冬植食者”的假说相符。展叶期越晚、叶片成熟速率越慢的树木，其植食性昆虫的种群丰度越低。本研究提出，叶片脱落与早期叶片物候均会显著影响植食性昆虫的种群丰度，并驱动植物防御策略的分化。叶片脱落可帮助树木摆脱已定植的植食者，使其需在春季重新完成种群定殖；但叶片保留时间最长的树种，同时也具备最强的针对植食性动物的直接防御能力。