Invasive species are one of the widespread stressors of aquatic ecosystems. Several studies document food web effects of invasive fish, but little information is available on the effects of invasive macrophytes. We studied differences in food chain length as well as trophic position and trophic diversity of fish and odonates in lakes dominated by native plants or invasive Eurasian watermilfoil. Trophic position and food chain length were determined using baseline-adjusted δ15N isotope signatures. Trophic diversity, or isotope niche width, was estimated from convex hull area analysis. Results show that trophic position of secondary consumers was not affected by the invasive macrophyte, whereas trophic diversity was greater in watermilfoil-dominated lakes. The direction of isotopic niche expansion was different in fish and odonates, suggesting potential decoupling in predator-prey interactions. This study shows that dominant non-native macrophytes may cause significant changes in food web structure of invaded ecosystems. Trophic diversity may be a more sensitive indicator of environmental stress than trophic position and has the potential to be used for assessment of invasive species impacts and restoration success.
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Acknowledgments We are grateful to Matthew Spickard, Krisan Webb, Jean Chervenak, and Dan Dugan for their assistance with data collection, Matt Roberts for suggestions on isotope analysis, and Gary Ervin, John Madsen, and Todd Tietjen for insightful comments on the earlier version of this manuscript. Financial support for this study was kindly provided by the Department of Wildlife and Fisheries, Mississippi State University and the Aquatic Ecosystem Restoration Foundation.
- Largemouth bass
- Myriophyllum spicatum
- Stable isotopes