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Publications (4 of 4) Show all publications
Thorp, J. H. & Bowes, R. E. (2017). Carbon Sources in Riverine Food Webs: New Evidence from Amino Acid Isotope Techniques. Ecosystems (New York. Print), 20(5), 1029-1041
Open this publication in new window or tab >>Carbon Sources in Riverine Food Webs: New Evidence from Amino Acid Isotope Techniques
2017 (English)In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Ecosystems, Vol. 20, no 5, p. 1029-1041Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer, 2017
Keywords
Flood pulse concept, Ohio river, river continuum concept, riverine ecosystem synthesis, river wave concept, upper Mississippi river
National Category
Ecology
Research subject
Biology
Identifiers
urn:nbn:se:kau:diva-69555 (URN)10.1007/s10021-016-0091-y (DOI)000407846100013 ()
Available from: 2018-10-10 Created: 2018-10-10 Last updated: 2018-10-22Bibliographically approved
Bowes, R. E., Thorp, J. H. & Reuman, D. C. (2017). Multidimensional metrics of niche space for use with diverse analytical techniques. Scientific Reports, 7, 1-11, Article ID 41599.
Open this publication in new window or tab >>Multidimensional metrics of niche space for use with diverse analytical techniques
2017 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, p. 1-11, article id 41599Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer, 2017
Keywords
Nitrogen isotopic composition, community-wide measures, food-web structure, amino-acids, stable-isotopes, trophic structure, ratios provide, fatty-acids, ecology, hydrogen
National Category
Ecology
Research subject
Biology
Identifiers
urn:nbn:se:kau:diva-69556 (URN)10.1038/srep41599 (DOI)000393140100001 ()
Available from: 2018-10-10 Created: 2018-10-10 Last updated: 2018-10-22Bibliographically approved
Bowes, R. E. & Thorp, J. H. (2015). Consequences of employing amino acid vs. bulk-tissue, stable isotope analysis: a laboratory trophic position experiment. Ecosphere, 6(1), 1-12
Open this publication in new window or tab >>Consequences of employing amino acid vs. bulk-tissue, stable isotope analysis: a laboratory trophic position experiment
2015 (English)In: Ecosphere, ISSN 2150-8925, E-ISSN 2150-8925, Ecosphere, Vol. 6, no 1, p. 1-12Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
John Wiley & Sons, 2015
Keywords
Compound specific stable isotope analysis, food chain length, fractionation, nitrogen
National Category
Ecology
Research subject
Biology
Identifiers
urn:nbn:se:kau:diva-69557 (URN)10.1890/ES14-00423.1 (DOI)000350440400014 ()
Available from: 2018-10-10 Created: 2018-10-10 Last updated: 2018-10-22Bibliographically approved
Bowes, R. E., Lafferty, M. H. & Thorp, J. H. (2014). Less means more: nutrient stress leads to higher delta N-15 ratios in fish. Freshwater Biology, 59(9), 1926-1931
Open this publication in new window or tab >>Less means more: nutrient stress leads to higher delta N-15 ratios in fish
2014 (English)In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 59, no 9, p. 1926-1931Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2014
Keywords
Food chain length, nitrogen, starvation, trophic position
National Category
Ecology
Research subject
Biology
Identifiers
urn:nbn:se:kau:diva-69558 (URN)10.1111/fwb.12396 (DOI)000339480500012 ()
Available from: 2018-10-10 Created: 2018-10-10 Last updated: 2018-10-22Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-5614-069x

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