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1. There is an urgent need to accurately model how environmental change affects the wide-scale functioning of ecosystems, but advances are hindered by a lack of knowledge of how trophic levels are linked across space. It is unclear which theoretical approach to take to improve modelling of such interactions, but evidence is gathering that linking species responses to their functional traits can increase understanding of ecosystem dynamics. Currently, there are no quantitative studies testing how this approach might improve models of multiple, trophically interacting species, at wide spatial scales. 2. Arable weeds play a foundational role in linking food webs, providing resources for many taxa, including carabid beetles that feed on their seeds and weed-associated invertebrate prey. Here, we model associations between weeds and carabids across farmland in Great Britain (GB), to test the hypothesis that wide-scale trophic links between these groups are structured by their species functional traits. 3. A network of c. 250 arable fields, covering four crops and most lowland areas of GB, was sampled for weed, carabid and invertebrate taxa over 3 years. Data sets of these groups were closely matched in time and space, and each contained numerous species with a range of eco-physiological traits. The consistency of trophic linkages between multiple taxa sharing functional traits was tested within multivariate and log-linear models. 4. Robust links were established between the functional traits of taxa and their trophic interactions. Autumn-germinating, small-seeded weeds were associated with smaller, spring-breeding carabids, more specialised in seed feeding, whereas spring-germinating, large-seeded weeds were associated with a range of larger, autumn-breeding omnivorous carabids. These relationships were strong and dynamic, being independent of changes in invertebrate food resources and consistent across sample dates, crops and regions of GB. 5. We conclude that, in at least one system of interacting taxa, functional traits can be used to predict consistent, wide-scale trophic links. This conceptual approach is useful for assessing how perturbations affecting lower trophic levels are ramified throughout ecosystems and could be used to assess how environmental change affects a wider range of secondary consumers.

1. Assuring future food productivity and security will require that better use is made of pest regulation provided by naturally occurring ecological services. However, empirical evidence of large-scale regulatory effects that might be employed in agriculture is still relatively scarce. 2. Using data from 257 conventionally managed arable fields at the UK national scale, we examine whether changes in the long-term store of weed seed in the seedbank are consistent with regulation by seed predatory carabid beetles. 3. We test three expectations of a simple conceptual model for carabid seed predation. The relationships we estimate are consistent with the model and suggest that carabid predation of weed seeds shed onto the soil surface changes the amount of seed returned to the seedbank bringing about seedbank change and regulation. 4. Granivorous and omnivorous carabids regulated seedbank abundance, with effects being observed on monocotyledon seedbank abundance, in all crops, and on total seedbank abundance, in spring maize and winter oilseed rape; effects that were robust across fields with differing pesticide management and between regions of the UK. 5. We found evidence of density dependence, with increasing amounts of seed rain leading to stronger regulation of the seedbank. 6. Our results also suggest that correlations between seed predators and seed rain abundance, which might be used to infer important effects of seed predators, do not provide sufficient evidence to indicate regulation of the weed seedbank. 7. Synthesis and applications. A major challenge for the future is to manage ecological, pest control services in place of current pesticides with little or no additional risk to productivity and food security. Our work shows that carabid seed predators have regulatory effects on the seedbank that appear general and robust across a range of current cropping and farm management situations at the national scale. Environmental Stewardship methods already exist across Europe to enhance carabid numbers in farmland. This means that carabid seed predators fit within a working framework that could be used to promote integrated pest management alongside or even in place of herbicides.

1. Several genetically modified herbicide-tolerant (GMHT) crops have cleared most of the regulatory hurdles required for commercial growing in the United Kingdom. However, concerns have been expressed that their management will have negative impacts on farmland biodiversity as a result of improved control given by the new herbicide regimes of the arable plants that support farmland birds and other species of conservation value. 2. The Farm-Scale Evaluations (FSE) project is testing the null hypothesis that there is no difference between the management of GMHT varieties of beet, oilseed rape and maize and that of comparable conventional varieties in their effect on the abundance and diversity of arable plants and invertebrates. The FSE also aims to estimate the magnitude and consider the implications of any differences that are found. 3. The experimental design of the FSE is a randomized block, with two treatments allocated at random to half-fields. The target sample is around 60-75 fields for each crop, selected to represent variation of geography and intensity of management across Britain. The experimental crops are managed by commercial farmers as if under commercial conditions. 4. Biodiversity indicators have been selected from plants and terrestrial invertebrates to identify differences between crop management regimes that may result in important ecological changes over larger scales of space and time. Field sampling is at fixed points, mainly along transects from the field boundary, starting before the crop is sown and continuing into following crops. 5. Synthesis and applications. The FSE is best considered as an investigation into the effects of contrasting crop management regimes on farmland biodiversity, rather than a study of the effects of genetic modification. It could become a model for future studies of ecological effects of the way we use and manage agricultural land.