Abstract

While plankton are often characterized by metabolism as either phototrophic primary producers or heterotrophic consumers, many actually combine photosynthesis and phagotrophy within a single cell. These “mixotrophic” plankton, which play an important biogeochemical role in marine food webs, exhibit diverse metabolic strategies with varied contributions from photosynthesis and phagotrophy. Mixotrophs co-exist with specialist phototrophs and heterotrophs, competing for shared resources; yet we do not know how this competition alters a mixotroph’s metabolic strategy or impacts biogeochemistry. We constructed a mathematical model to simulate the dynamics of a planktonic community which consists of mixotrophs and their specialist phototrophic competitor, phytoplankton. Our simulation demonstrates how the presence of competing phytoplankton causes metabolic character displacement, shifting mixotrophs to a more heterotrophic niche. We find that the displacement is affected by various environmental and physiological factors. For example, this displacement effect is temperature dependent, suggesting a link between community-level competitive mechanisms and global climate change. The proposed model therefore may be used to develop a more comprehensive analysis of the competition between constitutive mixotrophs and specialist phototrophs or heterotrophs. Our model also provides a mathematical framework for predicting constitutive mixotroph survival in the context of global warming.