Undercover predators: A meta-analysis of structural refuge impacts on invertebrate and vertebrate weed seed predation

Ecosystem services performed by animals who consume weed seeds have warranted steady research attention by agroecologists for more than thirty years. While many studies use seed removal assays to evaluate the relative importance vertebrate and invertebrate seed predators, the magnitude of their ecosystem services seems to be site and species specific. These strongly context-dependent effects suggest the need for a quantitative review of local factors that drive seed predation, as well as the seasonal dynamics of weed seed predation. We used meta-analysis techniques to evaluate the effects of vertebrate exclusion on seed removal over a seasonal gradient, and present a quantitative review of seed removal rates across weed species, crop types, and structural habitats. Synthesizing 26 studies, we learned that vertebrates contribute the most to seed loss during the spring, while invertebrates dominate seed predation in the autumn, with similar contributions from both groups during summer months. We found that seed predation by vertebrates and invertebrates is enhanced by a vegetative canopy, but depends on the structure of the crop habitat. These important trends will help to identify and promote environments where seed predators can have an agriculturally relevant impact on weed pressure.