Identifying important interaction modifications in ecological systems

Trophic interaction modifications, where a consumer-resource link is affected by additional species, are widespread and significant causes of indirect effects in ecological networks. The sheer number of potential interaction modifications in ecological systems poses a significant challenge, making prioritisation for empirical study essential. We use the trophic interaction modification framework to identify modifications that are most likely to exert significant effects on the dynamics of whole systems, introducing tools to quantify the topological relationship of interaction modifications relative to the underlying network. Using a set of simulated food webs and randomly distributed interaction modifications we test whether a subset of interaction modifications important for determining the local stability and directional determinability of complex networks can be identified. We show that trophic interaction modifications from rare species, those affecting high-flux interactions, those that connect species otherwise distantly linked, and those that act from high trophic level modifiers to interactions lower in the web have particular importance for dynamics. This work demonstrates that analysis of interaction modifications can be tractable at the network scale and highlights the importance of the inter-relationship between the structure of trophic networks and interaction modifications.