Seed predation is key to preventing population growth of the weed Alopecurus myosuroides

Seed predation can reduce the abundance and spread of unwanted vegetation in agricultural and other semi-natural ecosystems. However, knowledge of how variations in seed predation rates affect plant species population dynamics is needed for decision making and knowledge-based ecosystem management. We developed a stage-classified stochastic matrix population model for Alopecurus myosuroides Huds. (blackgrass), an annual plant species thriving as a weed in temperate agroecosystems of Western and Northern Europe. The model was parameterised using empirical demographic data from long-term experiments in Swedish winter wheat fields, including information on post-dispersal seed losses by vertebrate and invertebrate seed predators. For agroecosystems with highly effective weed control measures (e.g. chemical and mechanical weed control), model simulations showed that seed losses via seed predation need to reach at least 78% at peak seed shedding to suppress population growth of A. myosuroides. The field experiment showed that vertebrates were most important for seed predation in July, at peak seed shedding. In August, after crop harvest, invertebrates were responsible for almost all seed predation. The model indicated that weed seed predation was much more important for weed regulation when it occurred before crop harvest in July. Vertebrates most strongly reduced population growth of A. myosuroides, although both vertebrates and invertebrates were needed to prevent it entirely. Synthesis and applications. We showed that weed seed predation by vertebrate and invertebrate seed predators is key for reducing the population growth of winter annual weeds like A. myosuroides in intensively managed agroecosystems. Therefore, protection of weed seed predators is essential for making management of unwanted vegetation less dependent on chemical and mechanical measures