Core reorganisation in food webs buffers ecosystems against warming

Abstract Food webs are central to ecosystem functioning and stability, yet how they respond to climate warming at the substructural level remains unclear. We used a natural temperature gradient (5–25 °C) spanning 14 whole-stream ecosystems in Iceland to test how warming alters food web substructure organisation (core–periphery) and its consequences for ecosystem functioning (energy flux) and stability (robustness). We found no evidence that warming changed the number or proportion of core and peripheral species, but observed internal reorganisation driven by turnover in core species identity and abundance. While warming consistently decreased robustness to secondary extinctions through reduced food web connectance, core reorganisation enhanced both energy flux and robustness to species loss. Dynamic modelling showed ecosystems were disproportionately sensitive to the loss of core taxa, underscoring their structural importance. These results challenge the view of food webs as fixed hierarchies and reveal an adaptive internal architecture under warming, with core dynamics helping buffer ecosystem responses.