Abstract
Understanding the complexity of ecological communities is a long-standing challenge. Resolutions to this problem have largely focussed on trophic interactions, despite the acknowledged importance of non-trophic effects. Trophic interaction modifications, where a consumer-resource interaction is influenced by an additional species, are a major cause of non-trophic effects that have been demonstrated to exert strong influences on the dynamics of natural systems. They offer the potential to use information about trophic interactions to understand the structure and topology of non-trophic effects. Here we examine the impact of interaction modifications, introduced under a range of assumptions, on artificial and empirical trophic networks. We show that local stability and reactivity is critically dependent on the inter-relationship between the trophic and non-trophic interactions. Depending on their distribution, interaction modifications could significantly alter the overall structure of community interactions. Analyses of the stability of ecological systems based solely on trophic interactions are therefore unreliable, making empirical distributions of interaction modifications essential.