Core reorganisation in food webs buffers ecosystems against warming

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 organization (core–periphery) and its consequences for ecosystem functioning (energy flux) and stability (robustness). We found that warming does not alter the number or proportion of core and peripheral species but drives profound internal reorganization through 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 revealed that ecosystems were disproportionately more sensitive to the loss of core taxa, highlighting the importance of maintaining core size for ecosystem stability. These findings challenge the traditional view of food webs as fixed hierarchies, highlighting instead their adaptive internal architecture under environmental change. By uncovering a stabilizing mechanism rooted in core reorganisation, our work provides a new perspective on how ecosystems may buffer climate impacts.