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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.