Stoichiometry and growth kinetics in the "smallest zooplankton" - phagotrophic flagellates

, Abstract: A stoichiometric approach is applied to model nutrient element content and population growth kinetics in phagotrophic flagell~tes. Available evidence is limited, but suggests that the nutrient composition of flagellates is not strictly homeostatic, but instead varies with the nutrient element composition of their food resources. A mathe- matical model is constructed that couples the C, N, and P contents of flagellates to their population growth rate and the nutrient fluxes assimilated from food resources. Variants of the model are explored to examine the effects of saturating ingestion, main- tenance respiration, and selective feeding from food mixtures. In agreement with observations, the models predict non-homeostatic variation in the nutrient content of flagellates. Population growth rate is predicted to vary with both food quantity and quality (in terms of nutrient element content). It is proposed that lack of homeostasis and selective feeding on prey with high nutrient content enhance fitness of pha- gotrophic flagellates under some conditions.