Abstract
Networks of interspecific interactions drive community structure, dynamics and stability. The ability to infer interspecies interactions from observational field data would open possibilities to apply network models to manage real world ecosystems. Here, we show this is possible for a freshwater fish community in the Illinois River, United States, using long-term data collected through time and space. We solve the challenge of sparsely sampled field data using latent variable regression and constraints imposed by known trophic structure in the fish community. Network analysis indicates that the most abundant 9 fish coexisted thanks to equalizing mechanisms that reduced fitness differences between strong and weak competitors. Importantly, the network sheds light on the ongoing invasion by the exotic silver carp (Hypophthalmichthys molitrix), revealing that the invader outproduces native preys, replacing their contributions to the diets of native predators. Our work shows that field data and constrains imposed by known food webs can improve network inference and produce quantitative insights that could aid in conservation of freshwater ecosystems threatened by invasive species.