Planktonic Ecosystem Models: Perplexing Parameterizations and a Failure to Fail
Chapman Lecture Series

Dr. Peter Franks
Scripps Institution of Oceanography


Almost every planktonic ecosystem model being used today is based upon the same fundamental processes: Michaelis-Menten uptake of nutrients by the phytoplankton, and a saturating grazing response by the zooplankton. In tracing the history of the use of Michaelis-Menten kinetics in ecosystem models, the question arises whether this is the most appropriate way to represent nutrient uptake of a diverse phytoplanktonic community. While this nonlinear form may be a good representation of an enzyme, it is not clear that a changing community would necessarily show such a relationship of uptake rate with nutrient concentration. Furthermore, the way we have been using ecosystem models may be limiting our ability to understand the dynamics of marine ecosystems. Given that models are hypotheses, we should spend more time trying to reject them than trying to make them fit our data. Testing a suite of distinct models - hypotheses - may lead to stronger inferences about ecosystem structure and function. This testing requires sufficient data, particularly measurements of rates (e.g., nutrient uptake, grazing). Future research would benefit from a more intimate interaction and iteration between modeler and field scientist, models and data.

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