Variation in the Strength of Cascading Trophic Interactions Across a Riverscape

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Natural flow regimes of rivers are undergoing considerable modification due to global change and human use of water. This research will contribute to understanding how natural variation in flow influences the function of river ecosystems. The grazing of algae by insect larvae is a fundamentally important interaction in rivers that is affected by the flow regime. In some streams large amounts of algae result from 'trophic cascades' whereby predators like trout suppress grazing leading to increases in algae. In other streams insect grazers are able to keep algae in check. Extreme events like floods and droughts can influence grazer-algal interactions by affecting the abundance and type of grazers, numbers of trout, algal growth rates, and availability of nutrients. The effects of variation in flow regimes on grazer-algal interactions will be measured across a river-landscape to unravel the controls on the strength of trophic cascades. This work focuses on species interactions fundamental to many ecosystems; thus it will contribute to producing broadly applicable ecological generalities. Furthermore, the project builds on 30 years of research on streams in the East River valley near the Rocky Mountain Biological Laboratory in Western Colorado. The fate of water resources is hotly debated in Western Colorado, like many other areas around the world. By advancing understanding of the effects of natural variation in flow regimes on river inhabitants, the research will provide knowledge valuable for the management of rivers with human-induced changes to river flow.