Does stoichiometric variation in primary producers mediate coexistence in grazers?

在浮游植物中，由于光照和营养物质的可用性波动，藻类的营养化学计量也会发生变化。这种变化进一步受到生长速度的影响，在大多数情况下，这种影响最终体现在快速生长与藻类的某种最佳营养含量有关（生长速度越快变化越小），而缓慢生长的藻类可能具有大量不同的营养成分。这些模式是通过平均许多不同细胞的个体反应在藻类种群之间确定的，但到目前为止，还不清楚这是否也适用于单个藻类细胞之间的种群。因此，藻类生长速率与营养化学计量之间的联系是群体反应还是个体反应是一个悬而未决的问题。浮游动物通常具有更稳定的营养化学计量和更强的体内平衡程度。然而，同一物种的不同生命阶段可能有完全不同的营养需求。例如，在桡足动物中，快速生长的无肢动物比较老的桡足动物对磷的需求更高。因此，以幼龄期为主的桡足动物种群与以高龄期为主的种群相比，需要不同的最佳食物，如果不满足这些需求，生长将是次优的。在这里，我们将研究微藻种群生长速率的变化，将其与种群内营养化学计量学的变化联系起来，并研究这些生长速率引起的细胞营养配额变化对捕食者生长和动态的影响。如果种群内营养化学计量的变化随着藻类生长速度的减慢而增加，我们预测这将潜在地导致不同食物来源（具有不同的化学计量）的梯度。我们知道许多食草动物都是高度选择性的捕食者，所以如果生长速度较慢意味着不同藻类中不同营养化学计量的范围更广，这将为不止一种捕食者开辟潜在的生态位。理想情况下，在桡足类的情况下，nauplii将以种群中的高磷藻类为食，而桡足类应该消耗高氮隔间。因此，对一种资源的竞争将受到限制，因为在缓慢增长的人口中，实际上有不止一种资源。最终，这可能意味着初级生产者生长较慢的系统可能比藻类生长较高的系统维持更高的捕食者多样性。

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.