An attempt to identify the factors influencing weed seed predationin an area with large field sizes

Abstract: Granivores can contribute to long-term weed control by consuming substantialproportions of newly produced weed seeds in crop fields. In N-Germany, however, seed lossesand granivore densities tend to be lower than elsewhere. To investigate possible driving factors,seed predation rates were measured in six cereal fields. Factors under consideration were farmingsystem (organic or conventional), distances from the field edge (0-100m) and the relativecontributions of vertebrates and invertebrates to seed consumption. As expected, seed predationrates increased from early spring to early summer, after which they decreased again. Farmingsystem had little or no effect on seed predation rates. Seed predation by invertebrates wascomparable to that in other studies, but seed predation by vertebrates, mainly rodents, was muchlower. The effect of distance to the field edge on predation rates was variable and may be linkedto predator identity. Apart from the low vertebrate activity, no reasons could be identified for thelow seed predation rates. Some untested detrimental factor has to be involved, affecting bothconventional and organic fields. Alternatively, the impoverished landscape as a whole is toblame.