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  • 1.
    Bowes, Rachel E.
    et al.
    Kansas Biological Survey and Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, USA.
    Lafferty, M. Holliday
    Kansas Biological Survey and Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, USA.
    Thorp, James H.
    Kansas Biological Survey and Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, USA.
    Less means more: nutrient stress leads to higher delta N-15 ratios in fish2014Ingår i: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 59, nr 9, s. 1926-1931Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    1. Isotopic ratios of nitrogen are often used in food-web studies to determine trophic position (including food chain length) and food sources, with greater ratios of 15N/14N (d15N) usually considered indicative of higher trophic position. However, fasting and starving animals may also show a progressive increase in d15N over time as they catabolise their own tissues.

    2. To determine the importance of starvation, we conducted a 4-month laboratory experiment testing effects of starvation on body condition and isotope ratios in the muscle tissue of freshwater guppies (Poecilia reticulata). We also compared laboratory results and conclusions with analyses of body condition and isotope ratios in various small species of fish collected in four seasons from the Kansas River in north-eastern Kansas, U.S.A.

    3. Fish starved in our laboratory experiment had significantly higher 15N values and poorer body condition than those fed more regularly. The diverse group of fish species collected in summer (July) from the Kansas River had higher weight-to-length ratios and lower 15N values than those retrieved in other seasons. Overall body condition resulting from reduced food consumption explained 44 and 53% of the variability in 15N for field and laboratory fish, respectively.

    4. These results are applicable to a wide variety of food-web research but are especially pertinent to studies of organisms that undergo large changes in life history, dormancy, extended fasts or periods of significant nutritional allocation to young.

  • 2.
    Bowes, Rachel E.
    et al.
    Kansas Biological Survey, Lawrence, USA; Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, USA.
    Thorp, J. H.
    Kansas Biological Survey, Lawrence, USA; Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, USA.
    Consequences of employing amino acid vs. bulk-tissue, stable isotope analysis: a laboratory trophic position experiment2015Ingår i: Ecosphere, ISSN 2150-8925, E-ISSN 2150-8925, Ecosphere, Vol. 6, nr 1, s. 1-12Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An important metric of environmental health is food web structure because it reflects species richness, natural history diversity, and resource availability. While bulk-tissue stable isotope analysis has proven valuable for food web studies, field conditions may severely restrict its use and data can be quite variable. Amino acid stable isotope analysis potentially reduces this variability, in part by eliminating the need for signatures near the trophic base because a single top consumer contains both the primary producer signature (constant phenylalanine signature) and information reflecting number of trophic transfers (a progressively increasing d15N signature of glutamic acid). To evaluate the ecological sensitivity and cost/benefits of the techniques, we conducted a laboratory food chain experiment with four trophic levels. Water fleas (Daphnia magna) were cultured on a diet of powdered algae and then fed daily to guppies (Poecilia reticulata) for three months. These invertivorous fishes were then consumed by piscivororus bluegill sunfishes (Lepomis macrochirus) for a subsequent three months. All members of the food web were analyzed for 15N values and degree of fractionation using both bulk-tissue and amino acid stable isotope techniques. Our experiment demonstrated that the amino acid technique more accurately identified the true trophic position (TP) and food chain length (FCL ¼ maximum TP) with significantly less variability around mean values for each consumer trophic level. Moreover, use of amino acids requires significantly fewer replicates to identify TP. We discuss here the relative advantages and disadvantages of both approaches for determining TP and FCL and recommend that investigators switch as soon as possible to the amino acid isotope technique for determining FCL.

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  • 3.
    Bowes, Rachel E.
    et al.
    Kansas Biological Survey and Department of Ecology and Evolutionary Biology, University of Kansas, USA.
    Thorp, James H.
    Kansas Biological Survey and Department of Ecology and Evolutionary Biology, University of Kansas, USA.
    Reuman, Daniel C.
    Kansas Biological Survey and Department of Ecology and Evolutionary Biology, University of Kansas, USA; Laboratory of Populations, Rockefeller University, USA.
    Multidimensional metrics of niche space for use with diverse analytical techniques2017Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, s. 1-11, artikel-id 41599Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Multidimensional data are integral to many community-ecological studies and come in various forms, such as stable isotopes, compound specific analyses (e.g., amino acids and fatty acids), and both biodiversity and life history traits. Scientists employing such data often lack standardized metrics to evaluate communities in niche space where more than 2 dimensions are involved. To alleviate this problem, we developed a graphing and analytical approach for use with more than two variables, based on previously established stable isotope bi-plot metrics. We introduce here our community metrics as R scripts. By extending the original metrics to multiple dimensions, we created n-dimensional plots and metrics to characterize any set of quantitative measurements of a community. We demonstrate the utility of these metrics using stable isotope data; however, the approaches are applicable to many types of data. The resulting metrics provide more and better information compared to traditional analytic frameworks. The approach can be applied in many branches of community ecology, and it offers accessible metrics to quantitatively analyze the structure of communities across ecosystems and through time.

    Ladda ner fulltext (pdf)
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  • 4.
    Thorp, James H.
    et al.
    Kansas Biological Survey and Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, USA.
    Bowes, Rachel E.
    Kansas Biological Survey and Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, USA.
    Carbon Sources in Riverine Food Webs: New Evidence from Amino Acid Isotope Techniques2017Ingår i: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Ecosystems, Vol. 20, nr 5, s. 1029-1041Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A nearly 40-year debate on the origins of carbon supporting animal production in lotic systems has spawned numerous conceptual theories emphasizing the importance of autochthonous carbon, terrestrial carbon, or both (depending on river stage height). Testing theories has been hampered by lack of adequate analytical methods to distinguish in consumer tissue between ultimate autochthonous and allochthonous carbon. Investigators initially relied on assimilation efficiencies of gut contents and later on bulk tissue stable isotope analysis or fatty acid methods. The newest technique in amino acid, compound specific, stable isotope analysis (AA-CSIA), however, enables investigators to link consumers to food sources by tracing essential amino acids from producers to consumers. We used AA-CSIA to evaluate nutrient sources for 5 invertivorous and 6 piscivorous species in 2 hydrogeomorphically contrasting large rivers: the anastomosing Upper Mississippi River (UMR) and the mostly constricted lower Ohio River (LOR). Museum specimens we analyzed isotopically had been collected by other investigators over many decades (UMR: 1900–1969; LOR: 1931–1970). Our results demonstrate that on average algae contributed 58.5% (LOR) to 75.6% (UMR) of fish diets. The next highest estimated contributions of food sources were from C3 terrestrial plants (21.1 and 11.5% for the LOR and UMR, respectively). Moreover, results from 11 individually examined species consistently demonstrated the importance of algae for most fish species in these trophic guilds. Differences among rivers in relative food source availability resulting from contrasting hydrogeomorphic complexity may account for relative proportions of amino acids derived from algae.

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