Data and R codes for Zvereva et al. (2024): “Does spatial variation in insect herbivory match variations in plant quality? A meta-analysis”

Variation in herbivore pressure at different temporal and spatial scales has often been predicted from patterns in plant traits considered as antiherbivore defences. Here, we tested whether spatial variation in field insect herbivory is associated with the variation in plant quality for herbivores by conducting a meta-analysis of 223 correlation coefficients between herbivory levels and the expression of selected plant traits. We found no overall correlation between herbivory and either concentrations of plant secondary metabolites or values of physical leaf traits. This result was due to both the large number of low correlations and the opposing directions of high correlations in individual studies. Field herbivory demonstrated a significant association only with nitrogen: herbivore pressure increased with an increase in nitrogen concentration in plant tissues. Thus, our meta-analysis does not support either theoretical prediction, i.e. that plants possess high antiherbivore defences in localities with high herbivore pressure or that herbivory is low in localities where plant defences are high. We conclude that information about putative plant defences is insufficient to predict plant losses to insects in field conditions and that the only bottom-up factor driving spatial variation in insect herbivory is plant nutritive value, i.e. foliar nitrogen concentration.以往研究多依据被视作抗植食防御（antiherbivore defences）的植物性状的分布格局，来预测不同时空尺度下的植食压力变异。本研究通过对223组植食水平与选定植物性状表达量之间的相关系数开展元分析（meta-analysis），旨在检验野外昆虫植食的空间变异是否与植食动物的植物食料品质变异相关联。本研究未发现植食水平与植物次生代谢物（plant secondary metabolites）浓度或叶片物理性状数值之间存在整体相关关系。该结果源于两方面因素：一是大量低相关系数的研究占比颇高，二是单个研究中高相关系数的方向存在对立性。仅在植物组织氮浓度与野外植食水平间存在显著相关关系：植食压力随植物组织氮浓度升高而增强。因此，本元分析结果不支持任一理论预测，亦即两种理论预测分别为：在植食压力较高的生境中植物具备较强的抗植食防御能力，以及植物防御能力较高的生境中植食水平较低。综上，本研究认为，仅凭假定的植物防御性状相关信息不足以预测野外条件下植物被昆虫取食造成的损失；而驱动昆虫植食空间变异的唯一上行驱动因子，仅为植物营养品质，亦即叶片氮浓度。