Data from: Climate and leaf traits, not latitude, explain variation in plant‐herbivore interactions across a species’ range

Abstract1. Spatial variation in abiotic and biotic factors creates local contexts that influence the intensity of plant‐herbivore interactions. Some previous studies have accounted for the complexity of these interactions with latitudinal clines, while the absence of such clines in many other systems suggests other, often unknown, local community factors may instead explain the variation in herbivory across populations. 2. We investigated plant‐herbivore interactions across the entire range of a long‐lived tree (Quercus garryana), evaluating the relative importance of climate, latitude, population size, and insect feeding guilds in determining leaf phenotype and the extent and variation in insect herbivory. In this ecosystem, rain shadows create a nonlinear relationship between climate and latitude, allowing us to disentangle the effects of environmental factors. By performing similar analyses on trees grown in a common garden, we were able to assess the relative importance of environmental factors to leaf defence traits and herbivory. 3. Total herbivory varied significantly among populations, and was best explained by variation in spring precipitation, leaf traits, and tree population size, but not latitude. The relative importance of each of these factors changed over the growing season and with insect feeding guild. Conversely, damage in the common garden did not vary among trees from different origins when grown in a constant environment, leading us to believe variation in damage in natural populations is more likely the result of the local environments. 4. Leaf traits (trichome density and specific leaf area) varied significantly among populations, but neither showed an effect of latitude. Variation in both traits was best explained by tree size, and seasonal temperatures or precipitation. We found no variation in insect diversity among field populations, but abundance varied with mean summer precipitation and population size. 5. Synthesis: Seasonal precipitation consistently explained the geographic variation in the extent of herbivory to Q. garryana, while latitude and winter temperatures, factors that are commonly associated with latitudinal gradients in the intensity of species interactions, did not. Our findings highlight the importance of local climates and functional traits in shaping biotic interactions and intraspecific variation in plant‐insect interactions across large spatial scales.

摘要
1. 非生物与生物因子的空间变异会形成调控植物-植食者互作（plant-herbivore interactions）强度的局域环境。既往部分研究借助纬度梯度（latitudinal clines）阐释了这类互作的复杂性，但诸多其他研究体系中并未发现此类纬度梯度，这提示其他（通常尚不明确的）本地群落因子或许才是解释不同种群间植食作用差异的核心驱动因素。
2. 本研究针对长寿树种加里栎（Quercus garryana）的完整分布范围开展植物-植食者互作调查，评估气候、纬度、种群规模以及昆虫取食功能群（feeding guilds）在决定叶片表型、昆虫植食作用程度与变异幅度中的相对重要性。该生态系统内雨影效应（rain shadows）使得气候与纬度间呈现非线性关系，为我们厘清各类环境因子的独立作用提供了契机。通过对同质园（common garden）中栽植的植株开展平行分析，我们得以量化环境因子对叶片防御性状与植食作用的相对贡献度。
3. 不同种群的总植食作用程度存在显著差异，其中春季降水、叶片性状及树木种群规模的变异可最优解释该差异，而纬度则无显著解释效力。各因子的相对重要性会随生长季进程以及昆虫取食功能群的不同发生动态变化。与之相反，在同质园的统一环境下培育时，不同起源地的植株所受植食损伤并无显著差异，这表明自然种群中植食损伤的地理变异更可能由局域环境所主导。
4. 不同种群的叶片性状（毛状体密度与比叶面积）存在显著变异，但二者均未表现出纬度相关的响应规律。两类性状的变异均可通过树木体型、季节温度或降水得到最优解释。本研究未发现野外种群间昆虫多样性存在显著差异，但昆虫丰度随夏季平均降水与种群规模发生显著变化。
5. 总结：季节降水始终能解释加里栎植食作用程度的地理变异，而通常与物种互作强度纬度梯度相关的纬度与冬季温度则无此解释效力。本研究结果凸显了局域气候与功能性状在大空间尺度上调控生物互作以及植物-昆虫互作种内变异中的关键作用。