Interaction modification effects on ecological networks are affected by ratio dependence and network topology.

Interaction modification (IM), where one species modifies the strength of the density-mediated direct interaction between two other species, is an important ecological process, but little is known about the collective effect of multiple IM on overall community dynamics. We use stochastic bioenergetic modelling of ecological networks with different network topologies, functional responses and parameter values, to investigate the effects of IM connectance and IM strength on ecosystem properties including the evenness of species abundances and variability of system biomass. We found that the maximum system biomass that could potentially be attained by the model systems increased with IM connectance and strength when the models had nonrandom topology and prey-dependent functional responses as opposed to random topology and ratio-dependent responses. The maximum potential species evenness increased with IM strength but decreased with increasing IM connectance, when all modifications were negative. These findings underscore the importance of accounting for multiple IM across the community for understanding complex community dynamics.