Influence of nutrient supply and foraging behavior and life history of copepods on the dynamics of a widespread pelagic food web module

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The size structure of plankton communities strongly influences functional properties of pelagic ecosystems such as nutrient fluxes, primary and export production, and energy transfer up the food chain. In many marine and freshwater systems copepods play a key role in these processes and may act as a 'switch' between alternative food chains (a short, direct one from larger microphytoplankton to copepods and a longer one from small nanophytoplankton through ciliates to copepods). Together with the stock of inorganic nutrients, nanophytoplankton, microphytoplankton, ciliates and copepods form a pentagon in a food web graph. The role of copepods in pelagic food webs is modulated by nutrient and light supply, planktivore predation, and by behavioral and life history characteristics of the copepods. We propose to theoretically explore the influences of these modulating factors on pelagic ecosystem dynamics using the 'pentagon food web' as a tractable conceptual simplification. Specifically, we will use various extensions of a differential equation model of the pentagon module to ask how its dynamics are affected by (i) food choice behavior of copepods (e.g. switching), (ii) the supply with limiting nutrients (nitrogen and silicon), (iii) variation in the carbon to nutrient stoichiometry of phytoplankton, and (iv) by copepod stage structure, in particular stage-specific feeding and mortality rates. We expect to generate empirically testable hypotheses and to contribute to a deeper conceptual understanding of natural and anthropogenic influences on size structure, trophic structure and energy transfer through pelagic food webs.