Data from: Latitudinal patterns of herbivore pressure in a temperate herb support the biotic interactions hypothesis

The longstanding biotic interactions hypothesis predicts that herbivore pressure declines with latitude, but the evidence is mixed. To address gaps in previous studies, we measured herbivory and defense in the same system, quantified defense with bioassays, and considered effects of leaf age. We quantified herbivory and defense of young and mature leaves along a continental gradient in eastern North America in the native herb Phytolacca americana. Herbivory in the field declined with latitude and was strongly correlated with Lepidopteran abundance. Laboratory bioassays revealed that leaf palatability was positively correlated with latitude of origin. Young leaves were more damaged than mature leaves at lower latitudes in the field, but less palatable in bioassays. Both defense and palatability displayed non-linear latitudinal patterns, suggesting potential mechanisms based on biological or climatic thresholds. In sum, observational and experimental studies find patterns consistent with high herbivore pressure and stronger plant defenses at lower latitudes.长期以来的生物相互作用假说（biotic interactions hypothesis）预测，植食者压力随纬度升高而降低，但现有相关研究证据存在分歧。为填补既往研究的空白，本研究在同一研究体系中同步测定了植食程度与植物防御能力，采用生物测定法（bioassay）量化防御水平，并纳入叶龄的影响效应。本研究沿北美东部的大陆纬度梯度，针对本土草本植物商陆（Phytolacca americana）的幼叶与成熟叶，分别量化了其植食程度与防御能力。野外观测结果显示，植食程度随纬度升高而降低，且与鳞翅目（Lepidoptera）昆虫的丰度呈显著正相关。室内生物测定实验表明，叶片的适口性与其来源地的纬度呈显著正相关。野外观测中，低纬度地区的幼叶受损程度高于成熟叶，但在生物测定实验中其适口性反而更低。植物防御能力与叶片适口性均呈现非线性的纬度分布模式，这提示其背后可能存在基于生物学或气候阈值的调控机制。综上，本研究的观测与实验结果均支持低纬度地区植食者压力更高、植物防御能力更强的相关推论。