9Understanding the complexity of ecological communities is a long-standing challenge. Resolutions to 10 this problem have largely focussed on trophic interactions, despite the acknowledged importance of 11 non-trophic effects. Trophic interaction modifications, where a consumer-resource interaction is 12 influenced by an additional species, are a major cause of non-trophic effects that have been 13 demonstrated to exert strong influences on the dynamics of natural systems. They offer the 14 potential to use information about trophic interactions to understand the structure and topology of 15 non-trophic effects. Here we examine the impact of interaction modifications, introduced under a 16 range of assumptions, on artificial and empirical trophic networks. We show that local stability and 17 reactivity is critically dependent on the inter-relationship between the trophic and non-trophic 18 interactions. Depending on their distribution, interaction modifications could significantly alter the 19 overall structure of community interactions. Analyses of the stability of ecological systems based 20 solely on trophic interactions are therefore unreliable, making empirical distributions of interaction 21 modifications essential. 22Introduction 23