Understanding the nexus between hydrological alteration and biological invasions

The alteration of natural flow regimes by hydraulic infrastructure, exploitation for human uses, and changing climates has resulted in significant impacts on native species that inhabit freshwater ecosystems. Hydrologic alteration may promote new opportunities for nonnative species by creating novel habitats, modifying biotic interactions (including predation and competition), and promoting new dispersal pathways. Here, we review the relevant theory and current empirical evidence for additive, synergistic, and antagonistic interactions between hydrologic alteration and species invasions in flowing waters. Building on case studies of both animal and plant communities, we demonstrate the importance of the alteration-invasion nexus to mediate biotic interactions and alter food web structure via top-down and bottom-up effects. Finally, we describe how increasingly altered flow regimes and native-nonnative mixed communities pose a novel conservation challenge, and we explore emerging management strategies in highly-managed river basins.