Data from: Spatially heterogeneous perturbations homogenize the regulation of insect herbivores

Anthropogenic influences on resources and consumers can affect food web regulation, with impacts on trophic structure and ecosystem processes. Identifying how these impacts unfold is challenging because alterations to one or both resources and consumers can similarly transform community structure, especially for intermediate consumers. To date, empirical testing of perturbations on trophic regulation has been limited by the difficulty in separating the direct effect of perturbations on species composition and diversity versus those unfolding indirectly via altered feeding pathways. Moreover, disentangling the independent and interactive impacts of co-varying stressors that characterize human-altered systems has been an ongoing analytical challenge. We used a large-scale meta-community experiment in grasslands to test how resource inputs, stand perturbation, and spatial factors affect regulation of insect herbivores in tri-trophic grassland food webs. Using path-model comparisons, we observed significant simplification of food web regulation on insect herbivores, shifting from mixed predator-resource regulation in unaltered mainland areas, to strictly resource-based regulation with landscape perturbation and fragmentation. Most changes were attributed to homogenization of plant community caused by landscape fragmentation and the deterministic influence of eutrophication that reduced among-patch beta-diversity. This led to a simplified food web dominated by fewer, but more abundant herbivore taxa. Our work implies that anthropogenic perturbation relating to resources and spatial isolation can transform the regulation of food web diversity, structure and function.人类活动对资源与消费者的影响可干扰食物网调控，并对营养结构及生态系统过程产生影响。厘清此类影响的具体显现过程颇具挑战，因为无论是资源、消费者其一还是二者同时发生改变，均可能类似地重塑群落结构，对中间消费者而言尤为如此。迄今为止，由于难以区分扰动对物种组成与多样性的直接效应，以及通过取食通路改变间接产生的间接效应，针对营养调控扰动的实证检验始终受限。此外，厘清人类干扰生态系统中典型的协同变化胁迫因子的独立与交互影响，也是一项长期存在的分析难题。本研究依托草地大型集合群落（meta-community）实验，探究资源输入、群落扰动与空间因子如何调控三营养级（tri-trophic）草地食物网中的昆虫植食者。通过路径模型（path-model）对比分析，我们发现昆虫植食者所受的食物网调控显著简化：未受干扰的原生区域中为捕食者-资源混合调控模式，而在经历景观扰动与破碎化的区域则转变为严格的资源依赖型调控。此类变化大多源于景观破碎化引发的植物群落均质化，以及富营养化的确定性作用——二者均降低了斑块间的β多样性（beta-diversity）。这最终促成了食物网结构简化，其优势类群为数量更少但个体丰度更高的植食者类群。本研究结果表明，与资源及空间隔离相关的人类活动扰动，可改变食物网多样性、结构与功能的调控模式。