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Sökning: WFRF:(Carpenter Stephen R.) > (2003-2004)

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  • Pace, Michael L., et al. (författare)
  • Whole-lake carbon-13 additions reveal terrestrial support of aquatic food webs
  • 2004
  • Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 427:6971, s. 240-243
  • Tidskriftsartikel (refereegranskat)abstract
    • Ecosystems are supported by organic carbon from two distinct sources. Endogenous carbon is produced by photosynthesis within an ecosystem by autotrophic organisms. Exogenous carbon is produced elsewhere and transported into ecosystems. Consumers may use exogenous carbon with consequent influences on population dynamics, predator-prey relationships and ecosystem processes(1). For example, exogenous inputs provide resources that may enhance consumer abundance beyond levels supported by within-system primary production(2). Exogenous fluxes of organic carbon to ecosystems are often large, but this material is recalcitrant and difficult to assimilate, in contrast to endogenously produced organic matter, which is used more easily(3,4). Here we show, by the experimental manipulation of dissolved inorganic C-13 in two lakes, that internal primary production is insufficient to support the food webs of these ecosystems. Additions of NaH (CO3)-C-13 enriched the C-13 content of dissolved inorganic carbon, particulate organic carbon, zooplankton and fish. Dynamics of C-13 indicate that 40-55% of particulate organic carbon and 22-50% of zooplankton carbon are derived from terrestrial sources, showing that there is significant subsidy of these ecosystems by organic carbon produced outside their boundaries.
  • Cohen, Joel, et al. (författare)
  • Ecological community description using the food web, species abundance, and body size
  • 2003
  • Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 100:4, s. 1781-1786
  • Tidskriftsartikel (refereegranskat)abstract
    • Measuring the numerical abundance and average body size of individuals of each species in an ecological community's food web reveals new patterns and illuminates old ones. This approach is illustrated using data from the pelagic community of a small lake: Tuesday Lake, Michigan, United States. Body mass varies almost 12 orders of magnitude. Numerical abundance varies almost 10 orders of magnitude. Biomass abundance (average body mass times numerical abundance) varies only 5 orders of magnitude. A new food web graph, which plots species and trophic links in the plane spanned by body mass and numerical abundance, illustrates the nearly inverse relationship between body mass and numerical abundance, as well as the pattern of energy flow in the community. Species with small average body mass occur low in the food web of Tuesday Lake and are numerically abundant. Larger-bodied species occur higher in the food web and are numerically rarer. Average body size explains more of the variation in numerical abundance than does trophic height. The trivariate description of an ecological community by using the food web, average body sizes, and numerical abundance includes many well studied bivariate and univariate relationships based on subsets of these three variables. We are not aware of any single community for which all of these relationships have been analyzed simultaneously. Our approach demonstrates the connectedness of ecological patterns traditionally treated as independent. Moreover, knowing the food web gives new insight into the disputed form of the allometric relationship between body mass and abundance.
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