Does stoichiometric variation in primary producers mediate coexistence in grazers?

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In phytoplankton, as the availability of light and nutrients fluctuate, there is variation in the nutrient stoichiometry of the alga. This variation is further influenced by growth rates, which culminates in most cases in the fact that fast growth is linked with a certain optimal nutrient content of the algae (less variation at higher growth rate), whereas slow growing algae can have a large array of different nutrient compositions. These patterns were identified between populations of algae by averaging the individual responses of many different cells, but up until now, it is unclear whether this also holds within populations, between single algal cells. Thus, it is an open question whether the link between growth rate and nutrient stoichiometry of algae is a population response or an individual response.Zooplankton typically has a more constant nutrient stoichiometry, and a stronger degree of homeostasis. However, different life-stages of the same species can have completely different nutritional requirements. For example in copepods, fast growing nauplii have a higher demand for phosphorus than older copepodite stages. As a result, a copepod population dominated by nauplii will require different optimal food than a population dominated by older stages, and growth will be suboptimal if these requirements are not met. Here, we will investigate variation in population growth rate in microalgae, link this to intra-population variation in nutrient stoichiometry, and investigate the effect of these growth rate-induced variations in cell nutrient quota on growth and dynamics of predators. If intra-population variation in nutrient stoichiometry increases with slower algal growth rates, we predict that this will potentially lead a gradient of different food sources (with different stoichiometry) being available. We know that many herbivores are highly selective predators, so if slower growth means a wider range of different nutrient stoichiometry in the different algae, this would open up potential niches for more than one predator. Ideally, in the case of the copepods, the nauplii would feed on the high P algae in the population whereas the copepodits should consume the high N compartment. Thus, the competition for one resource would be restricted, because within a slow growing population there are in fact more than one resource. Ultimately, this might mean that systems with slower growing primary producers might sustain a higher diversity of predators than those where algal growth is higher.