Prey-abundance affects zooplankton assimilation efficiency and the outcome of biogeochemical models

Aquatic biogeochemical models that include zooplankton feeding on phytoplankton assess a range of ecologically important issues. Such models generally assume assimilation efficiency (e) to be invariant with prey abundance. We first review the literature and make a strong case for recognising and quantifying the general dependence of e on prey abundance. Then, using two standard, fundamental multi-trophic models (the Rosenzweig–MacArthur, RM, predator–prey couplet and the nutrient-phytoplankton-zooplankton, NPZ, models) we explore how varying e with prey abundance alters the outcome of models. Incorporating variable e into both models altered their dynamics, potentially in important and counterintuitive directions. We suggest there is now a need for further empirical consideration of the extent to which zooplankton e changes with phytoplankton abundance, specifically focusing on the shape of this response, and then for continued assessment of the impact of variable e on model dynamics.