Warming and Species Richness Weaken Eco-Phenotypic Feedback Loop in Long-Term Natural Ecosystems

Eco-phenotypic feedback-reciprocal interactions between phenotypic traits and ecological dynamics-is increasingly recognised as a driver of biodiversity patterns, species interactions and ecosystem functioning. Through this feedback, phenotypic traits such as body size can rapidly respond to environmental variation through plastic or evolutionary changes, altering population abundance, which in turn feeds back to shape the trait dynamics. Yet, whether the strength of this feedback remains stable under environmental change remains unclear. Using long-term monitoring data from 101 aquatic and terrestrial ecosystems encompassing multiple generations, we provide the first synthesis showing that warming and species richness systematically weaken the eco-phenotypic feedback loop, whereas species with larger median body size exhibit stronger feedback. Our findings reveal that climate change can erode key trait-demography couplings and highlight the importance of integrating eco-phenotypic frameworks into global change research.