Predator species are disproportionately vulnerable to human-caused extinction and their loss can trigger ecosystem altering trophic cascades. Elucidation of the consequences of predator biodiversity loss is therefore central to forecasting how ecosystems will respond to real-world losses of biodiversity. Experiments to date reveal a high degree of variability around effects of predator species losses, leading to high uncertainty of predictions. The Aim of the project proposed here is to develop a predictive understanding of the cascading effects of predator species loss. Two key sources of variability in effects of predator species loss are hypothesized, both based on the functional traits of predators. An experimental approach is proposed involving an international network of collaborators to identify key functional traits underlying the direct and interactive effects of multiple predators on their prey and ecosystem functioning . Once identified, key traits of predators will be challenged to explain and predict the effects of predator species loss in novel contexts and across different systems.