Seed size predicts global effects of small mammal seed predation on plant recruitment.

Recent studies demonstrate that by focusing on traits linked to fundamental plant life-history trade-offs, ecologists can begin to predict plant community structure at global scales. Yet, consumers can strongly affect plant communities, and means for linking consumer effects to key plant traits and community assembly processes are lacking. We conducted a global literature review and meta-analysis to evaluate whether seed size, a trait representing fundamental life-history trade-offs in plant offspring investment, could predict post-dispersal seed predator effects on seed removal and plant recruitment. Seed size predicted small mammal seed removal rates and their impacts on plant recruitment consistent with optimal foraging theory, with intermediate seed sizes most strongly impacted globally - for both native and exotic plants. However, differences in seed size distributions among ecosystems conditioned seed predation patterns, with relatively large-seeded species most strongly affected in grasslands (smallest seeds), and relatively small-seeded species most strongly affected in tropical forests (largest seeds). Such size-dependent seed predation has profound implications for coexistence among plants because it may enhance or weaken opposing life-history trade-offs in an ecosystem-specific manner. Our results suggest that seed size may serve as a key life-history trait that can integrate consumer effects to improve understandings of plant coexistence.