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Toward Canonical Trophic Aggregations
Robert E. Ulanowicz and W. Michael Kemp
The American Naturalist
Vol. 114, No. 6 (Dec., 1979), pp. 871-883
Stable URL: http://www.jstor.org/stable/2460557
Page Count: 13
You can always find the topics here!Topics: Ecosystems, Aggregation, Trophic levels, Respiration, Matrices, Ecology, Marine ecosystems, Species, Thermodynamics, Marine ecology
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Steady-state input-output analysis of energy flows in an ecosystem conveniently delineates the discrete steps of energy processing in a given ecosystem. The fraction of a specific flow between species which results from a given input via any integral number of transfers can be calculated. The portions of all flows which are the same number of steps from any external input may, therefore, be aggregated. Furthermore, the mapping which creates these groupings preserves the first and second laws of thermodynamics. The aggregated compartments are "trophic" in the sense that they are ordered according to the number of transfers from an external input. They do not, however, represent a sequential chain of energy flow in the strict sense. Transfers between compartments which are not nearest neighbors in the chain are still present. A secondary transformation which decouples the exchanges between non-neighboring compartments can be effected. In the resultant chain of flows more energy appears to be dissipated in the lower trophic levels. There is no a priori reason why the second law of thermodynamics should be preserved under the second transformation.
The American Naturalist © 1979 The University of Chicago Press