Biological control of weed patches by seed predators; responses to seed density and exposure time

Weeds typically occur in patches of different sizes and densities. Post-dispersal seed predators contribute to biological weed control by removing newly produced weed seeds before they can enter the seedbank. Seed predation can limit weed population growth if seed predators respond to seed densities so that seed predation is highest within weed patches. To determine whether this relationship holds for Echinochloa crus-galli seeds in corn fields, we observed the levels and responses of seed predators to different densities of E. crus-galli seeds during autumn in 2014 and 2015 (August until corn harvest in September-October) and during the winter of 2014 (August 2014 until March 2015) in three corn fields. We tested whether seed predation in autumn is a good estimate of seed predation from seed shed until the following spring (autumn plus winter), because seed predators were assumed to be less active during winter. In autumn 2014, the levels of seed predation and the response to seed density differed between fields because the main type of seed predator varied between fields. In autumn 2015, almost all seeds were lost due to seed predation in all fields, probably because of a high abundance of rodents. A response to seed density could not be detected. Seed predation during winter resulted partially in an increased level and a density independent response to seed density in all fields. Seed predation in autumn does not reflect seed predation from seed shed until the following spring. Furthermore, the effect of seed predation on weed population dynamics will differ between years and fields.