Abstract Methods to predict ecosystem responses to changing environmental conditions, including options for mitigation and management, are vital for scientists and policy makers. We propose that modelling ecosystems by grouping species into trophic-functional types has great utility, because it is potentially generic and applicable to any ecosystem. Here we describe in details a trophic-functional ecosystem model of arable agriculture (the TrophicLINK model), constructed using an individual-based model, and present some supporting sensitivity tests of the model performing according to our expectations for the arable ecosystem. We vary parameters for particular plant and invertebrate trophic-functional types and we show that the model is sensitive to the values chosen. Though this trophic-functional method for modelling ecosystems will be subject to further sensitivity tests and empirical validation, we argue that the modelling structure is fit for investigating the impact of changes in agro-ecosystems.