Baraibar B, Daedlow D, De Mol F & Gerowitt B (2011). Density dependence of weed seed predation by invertebrates and vertebrates in winter wheat. Weed Research 52, 79–87.
Weed seed predation has the potential to limit weed population growth within agricultural fields. Its success depends in part on the ability of predators to detect weed patches and respond in a direct density-dependent way to increasing weed seed densities. To test for density-dependent responses, an experiment was conducted in north-eastern Germany in four winter wheat fields during October 2008 and 2009. Zero, 1000, 2500 and 5000 seeds m−2 of Lolium multiflorum were applied to four adjacent 15 m × 15 m plots in each field. Seed predation was measured in 20 randomly located trays per plot that were accessible to all predators (eight per plot) or excluded vertebrates (12 per plot). Seeds were exposed in the field for 18 days. Remaining seeds were recovered from the soil and counted. In addition, 20 seed cards were randomly placed in each plot, half of them with vertebrate exclosure cages. Seeds on cards were counted every other day. Seed predators were identified. Predation rates measured by trays were low (32.7% per 18 days) and may have been caused by low densities of predators. Vertebrates responded in a direct density-dependent way to increasing seed densities, whereas the response of invertebrates was density independent. Seed predation from seed cards confirmed the density-dependent responses obtained using trays. Seed predators only needed a few days to detect and preferably exploit the high density plots. Weed seed patches are likely to persist in fields where invertebrates are the main predators, while they could be better controlled where granivorous rodents predominate.