Collaborative Research: Reverberating Responses to Trophic Cascades across Ecosystems: from Land to Streams and Back Again

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The many interconnected relationships between predators and prey in a food web can link seemingly distant organisms and processes. This study explores how the influence of top predators in a terrestrial environment is linked across ecosystem boundaries to impact primary production and food webs in aquatic environments. This study also explores how aquatic ecosystem responses to predators can reverberate back out of the stream to impact terrestrial predators that rely on the export of emerging adult insects from the stream. Cross-ecosystem food web connections will be studied at three different National Parks (Zion, Rocky Mountain, and Yellowstone National Parks), thereby providing replication at large spatial scales and leveraging the opportunities that National Parks provide to educate the public about food web ecology and the role of top predators in structuring our ecosystems. This research will be the first of its kind to investigate reverberating effects of trophic cascades whereby indirect effects may cross ecosystem boundaries (terrestrial to aquatic) and then subsequently reverberate back to animals and plants in the original ecosystem (aquatic back to terrestrial). This work will provide a more complete picture of how the loss of top predatory species worldwide may be indirectly influencing many distantly connected species.Previous investigations have demonstrated the indirect role of top predators (e.g., wolves in Yellowstone Park and mountain lions in Zion National Park) in control of riparian vegetation along streams. In addition, streams and riparian zones are connected by well-understood processes of material and organism exchange, making them ideal systems to identify and quantify trophic reverberations. The study will be conducted in streams and adjacent riparian zones and will encompass (1) streamside ungulate browsing and riparian plant communities, (2) community composition and abundance of in-stream biota, quantification of terrestrial fluxes (organic matter and invertebrate) fluxes to streams, and diets of stream biota, and (3) emergent adult aquatic insects in the riparian zone and the response of spiders and bats. These riparian insectivores serve as a bellwether for changes in stream insect emergence and stream-riparian linkages. In each park, replicate study sites will be established along streams with and without controls on ungulate browsing of riparian woody vegetation. By comparing within and across three national parks, this study will yield a greater understanding of how community and landscape context may mediate the strength, or even sign, of reverberating responses to terrestrial top-down control of ungulate browsing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.