In riparian areas, terrestrial and aquatic habitats overlap, creating a zone where they interact, the aquatic-terrestrial interface. Coupling of the two systems allows for movement of energy between them and generates intertwining food webs. As a result, riparian consumers, such as fish or birds, have alternative prey items external to their respective habitats. Energy flows between aquatic and terrestrial habitats, creating what some have called an ecological subsidy. Subsidies can occur in many situations; in this study we are examining reciprocal subsidies to terrestrial and aquatic predators in a riparian area.
Emerging aquatic insects are available to riparian avian consumers, and terrestrial invertebrates may be consumed by fish. But to what extent are the consumers utilizing these alternative prey sources? We are examining riparian food webs in three Oregon Coast Range watersheds by sampling aquatic and terrestrial insects, riparian birds, and fish. Through the use of mist netting, fecal and feather samples from birds have been collected. Fecal analysis will potentially provide direct evidence of how aquatic secondary production is subsidizing riparian insectivorous birds. Analysis of feather samples will be used to determine avian diet and to compare the isotopic signatures found in the tissue to food items found in the fecal samples. Fish diet will be analyzed directly through stomach content samples. Both will be compared to the composition and availability of aquatic and terrestrial invertebrates collected from four sampling methods.
By using these techniques in different seasons, we will estimate interdependence among these groups. We hope to address the following questions: Are fish able to utilize terrestrial insects in times when benthic invertebrates are naturally low? Is the emergence of aquatic insects essential to birds in times when energy demands are high?
For additional information about this research study see
the 2005 CFER
Annual Report. (2.2 MB)
