Data from: Plant functional traits reveal the relative contribution of habitat and food preferences to the diet of grasshoppers

Food preferences and food availability are two major determinants of the diet of generalist herbivores and of their spatial distribution. How do these factors interact and eventually lead to diet differentiation in co-occurring herbivores? We quantified the diet of four grasshopper species co-occurring in subalpine grasslands using DNA barcoding of the plants contained in the faeces of individuals sampled in the field. The food preferences of each grasshopper species were assessed by a choice (cafeteria) experiment from among 24 plant species common in five grassland plots, in which the four grasshoppers were collected, while the habitat was described by the relative abundance of plant species in the grassland plots. Plant species were characterised by their leaf economics spectrum (LES), quantifying their nutrient vs. structural tissue content. The grasshoppers’ diet, described by the mean LES of the plants eaten, could be explained by their plant preferences but not by the available plants in their habitat. The diet differed significantly across four grasshopper species pairs out of six, which validates food preferences assessed in standardised conditions as indicators for diet partitioning in nature. In contrast, variation of the functional diversity (FD) for LES in the diet was mostly correlated to the FD of the available plants in the habitat, suggesting that diet mixing depends on the environment and is not an intrinsic property of the grasshopper species. This study sheds light on the mechanisms determining the feeding niche of herbivores, showing that food preferences influence niche position whereas habitat diversity affects niche breadth.

食物偏好与食物可获得性是决定广食性植食动物（generalist herbivores）食谱及其空间分布的两大核心因素。这些因素如何相互作用，最终导致同域共存植食动物的食谱分化？本研究针对野外采集的4种同域分布于亚高山草地的蝗虫物种，通过对其粪便中所含植物进行DNA条形码（DNA barcoding）分析，量化了各物种的食谱组成。针对采集这4种蝗虫的5个草地样地中常见的24种植物，通过自助餐选择（cafeteria）实验评估了每种蝗虫的食物偏好；同时以草地样地内植物物种的相对多度来表征生境特征。植物物种通过叶片经济谱（leaf economics spectrum, LES）进行表征，该指标可量化植物养分组织与结构组织的相对含量。以取食植物的平均叶片经济谱值表征的蝗虫食谱，可通过其植物偏好得到解释，但无法通过生境中可获得的植物类群来解释。6组蝗虫物种对中，有4组的食谱存在显著差异，这证实了标准化条件下评估的食物偏好可作为自然生态系统中食谱分区的有效指标。与之相反，食谱中叶片经济谱的功能多样性（functional diversity, FD）变异大多与生境中可获得植物的功能多样性呈显著相关，这表明食谱混合程度取决于环境条件，而非蝗虫物种的固有属性。本研究阐明了决定植食动物取食生态位的核心机制：食物偏好影响生态位位置，而生境多样性则调控生态位宽度。