| 1. |
- Bowes, Rachel E., et al.
(författare)
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Less means more : nutrient stress leads to higher delta N-15 ratios in fish
- 2014
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Ingår i: Freshwater Biology. - : Wiley-Blackwell. - 0046-5070 .- 1365-2427. ; 59:9, s. 1926-1931
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Bowes, Rachel E., et al.
(författare)
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Multidimensional metrics of niche space for use with diverse analytical techniques
- 2017
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Ingår i: Scientific Reports. - : Springer. - 2045-2322. ; 7, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Bowes, Rachel E., et al.
(författare)
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Reweaving river food webs through time
- 2020
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Ingår i: Freshwater Biology. - : Wiley-Blackwell. - 0046-5070 .- 1365-2427. ; 65:3, s. 390-402
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Tidskriftsartikel (refereegranskat)abstract
- Our project sought to determine ecological effects of adding low-head dams and levees to large rivers by examining potential changes to aquatic food webs over a 70-year period in the Lower Ohio River (LOR) and Upper Mississippi River (UMR). We employed museum collections of fish and compound specific stable isotope analysis of amino acids to evaluate long-term changes in primary food sources for multiple species of fish in each river. Fishes in both rivers depended more on autochthonous than allochthonous carbon sources throughout the 70-year period (based on measurements of isotopic signatures of algae, C-3 plants, C-4 plants, cyanobacteria, and fungi), but the relative use of different carbon sources differed between the UMR and LOR. Significant but opposite shifts in trophic positions (TP) between rivers over time (higher TP in the UMR; lower in the LOR) were correlated with major anthropogenic changes to habitat structure (e.g. slight decrease in abundance of side channels in the UMR; increase in pool water depth in the LOR) resulting from low-head dam construction. They may also have been influenced by likely increased primary productivity in the UMR from agricultural nitrogen inputs and by possible shifts in the importance of phytoplankton versus benthic algae in the LOR from changes in water depth. Shifts in trophic position and reliance on various food sources were not correlated with variation in discharge, gage height, or temperature. Although these two rivers have contrasting hydrogeomorphic complexity (UMR is an anastomosing river, while the LOR is a constricted channel river) and different discharge patterns (seasonal versus yearly operation in some cases), both differ substantially from rivers having hydrogeomorphic changes resulting from construction of high dams (>15 m). It is not surprising, therefore, that factors controlling trophic position and reliance on different carbon sources vary among different types of dams and river structures.
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| 4. |
- Brett, Michael T., et al.
(författare)
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How important are terrestrial organic carbon inputs for secondary production in freshwater ecosystems?
- 2017
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Ingår i: Freshwater Biology. - : WILEY. - 0046-5070 .- 1365-2427. ; 62:5, s. 833-853
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Forskningsöversikt (refereegranskat)abstract
- 1. Many freshwater systems receive substantial inputs of terrestrial organic matter. Terrestrially derived dissolved organic carbon (t-DOC) inputs can modify light availability, the spatial distribution of primary production, heat, and oxygen in aquatic systems, as well as inorganic nutrient bioavailability. It is also well-established that some terrestrial inputs (such as invertebrates and fruits) provide high-quality food resources for consumers in some systems. 2. In small to moderate-sized streams, leaf litter inputs average approximately three times greater than the autochthonous production. Conversely, in oligo/mesotrophic lakes algal production is typically five times greater than the available flux of allochthonous basal resources. 3. Terrestrial particulate organic carbon (t-POC) inputs to lakes and rivers are comprised of 80%-90% biochemically recalcitrant lignocellulose, which is highly resistant to enzymatic breakdown by animal consumers. Further, t-POC and heterotrophic bacteria lack essential biochemical compounds that are critical for rapid growth and reproduction in aquatic invertebrates and fishes. Several studies have directly shown that these resources have very low food quality for herbivorous zooplankton and benthic invertebrates 4. Much of the nitrogen assimilated by stream consumers is probably of algal origin, even in systems where there appears to be a significant terrestrial carbon contribution. Amino acid stable isotope analyses for large river food webs indicate that most upper trophic level essential amino acids are derived from algae. Similarly, profiles of essential fatty acids in consumers show a strong dependence on the algal food resources. 5. Primary production to respiration ratios are not a meaningful index to assess consumer allochthony because respiration represents an oxidised carbon flux that cannot be utilised by animal consumers. Rather, the relative importance of allochthonous subsidies for upper trophic level production should be addressed by considering the rates at which terrestrial and autochthonous resources are consumed and the growth efficiency supported by this food. 6. Ultimately, the biochemical composition of a particular basal resource, and not just its quantity or origin, determines how readily this material is incorporated into upper trophic level consumers. Because of its highly favourable biochemical composition and greater availability, we conclude that microalgal production supports most animal production in freshwater ecosystems.
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| 5. |
- Maasri, Alain, et al.
(författare)
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A global agenda for advancing freshwater biodiversity research
- 2022
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 25:2, s. 255-263
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Tidskriftsartikel (refereegranskat)abstract
- Global freshwater biodiversity is declining dramatically, and meeting the challenges of this crisis requires bold goals and the mobilisation of substantial resources. While the reasons are varied, investments in both research and conservation of freshwater biodiversity lag far behind those in the terrestrial and marine realms. Inspired by a global consultation, we identify 15 pressing priority needs, grouped into five research areas, in an effort to support informed stewardship of freshwater biodiversity. The proposed agenda aims to advance freshwater biodiversity research globally as a critical step in improving coordinated actions towards its sustainable management and conservation.
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| 6. |
- Thorp, James H., et al.
(författare)
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Carbon Sources in Riverine Food Webs : New Evidence from Amino Acid Isotope Techniques
- 2017
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Ingår i: Ecosystems (New York. Print). - : Springer. - 1432-9840 .- 1435-0629. ; 20:5, s. 1029-1041
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Tidskriftsartikel (refereegranskat)abstract
- 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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