Flexibility in Aquatic Food Web Interactions: Linking Scales and Approaches

Abstract Trophic interactions determine food web structure and influence biodiversity, community structure, ecosystem functioning, and food web responses to global change. These interactions are highly flexible, changing on temporal scales from diurnal to evolutionary times due to phenotypic plasticity, rapid evolution and species sorting. Small-scale experimental and theoretical studies of plankton interactions have demonstrated a high relevance of this flexibility for community dynamics and ecosystem processes in small, simplified communities. However, the extent to which this flexibility affects larger-scale systems, for example, global ocean dynamics and their responses to global change, is still poorly understood. Differences in methodology, focus and terminology between research disciplines limit our ability to project established effects of flexible trophic interactions onto larger spatial and temporal scales. We propose to bridge this gap with a general framework for upscaling knowledge from small-scale research to large-scale models. Building on examples from plankton communities, we use this framework to show how mechanisms demonstrated in small-scale studies can be linked to ecosystem functions relevant at large scales. We argue for incorporating flexibility in large-scale process-based models to improve their realism and predictive power, and discuss challenges and ways forward for achieving this. Finally, we suggest several concrete ways for upscaling small-scale studies to make their findings more relevant for large-scale research, to close existing knowledge gaps and to improve our understanding of how flexible trophic interactions affect dynamics and processes across scales.