Thursday, May 29, 2008 - 3:00 PM
569

Building an ecological time machine: Use of museum specimens to examine historical changes in riverine food webs

Michael D. Delong1, James H. Thorp2, and Jeffrey Anderson1. (1) Large River Studies Center, Winona State University, Biology Department, Winona, MN 55987, (2) Ecology and Evolutionary Biology, University of Kansas, 2101 Constant Avenue, Lawrence, KS 66047-3759

Ecologists often wish it were possible to travel back in time to understand the nature of ecosystems subjected to human modifications.  Recent studies have demonstrated that preservation creates small but predictable changes in the carbon and isotope ratios of animals.  We obtained samples of fish, mussels, and gastropods for determination of stable isotope ratios to examine how food chain length of rivers has changed over time, particularly in response to anthropogenic disturbances.  Organic samples (n=7,000) were obtained from a number of museums for eight rivers, with samples covering a period from the mid-19th century to the present.  Carbon and nitrogen isotope ratios of fish and mussels have changed in both the Upper Mississippi (1880 – 2000) and Ohio (1935 – 2000) rivers by 2 - 5 ppt. Estimates of the contribution of food sources to fish from the Ohio River indicates a shift from benthic to pelagic sources, which is supported by the observed changes in δ13C.  In contrast, isotopic ratios of fish from the St. Croix River, a minimally disturbed river, has remained unchanged. Calculation of trophic measures using historic isotopic data will help to elucidate the nature of changes and identify possible mechanisms for shifts in riverine food webs.


Web Page: food web, disturbance, stable isotope

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