Predator traits determine food-web architecture across ecosystems

Predator–prey interactions in natural ecosystems generate complex food websthat have a simple universal body-size architecture where predatorsare systematically larger than their prey. Food-webtheory shows that the highest predator–prey body- mass ratiosfound in natural food websmay be especially important because they create weak interactions with slow dynamics that stabilize communities against perturbations and maintain ecosystem functioning. Identifying these vital interactions in real communities typically requires arduous identification of interactions in complex food webs. Here, we overcome this obstacle by developing predator-trait models to predict average body- mass ratiosbased on a database comprising 290 food websfrom freshwater, marine and terrestrial ecosystemsacross all continents. We analysed how species traits constrain body-size architecture by changing the slope of the predator–prey body-mass scaling. Across ecosystems, we found high body- mass ratiosfor predatorgroups with specific trait combinations including (1) small vertebrates and (2) large swimming or flying predators. Including the metabolic and movement types of predatorsincreased the accuracy of predicting which species are engaged in high body- mass ratiointeractions. We demonstrate that species traits explain striking patterns in the body-size architecture of natural food websthat underpin the stability and functioning of ecosystems, paving the way for community-level management of the most complex natural ecosystems.