Effect of trait variability on the dynamics of coupled, bi-trophic plankton - biofilm systems

许多生态过程都是由捕食者与猎物的相互作用引起的。因此，为了更深入地了解生态系统的动态和功能，研究这些相互作用是非常有意义的。几个例子表明，被捕食物种可以发展出防御表型，以减少捕食，从而降低死亡率。然而，这种防御机制可能要付出相当大的代价，而且只有在捕食者密度很高的情况下才会有回报，而这种情况可能只是暂时发生的。此外，如果猎物受到不同捕食者的捕食，特别是当防御特征是特定的和不相容的捕食者时，防御成本可能会急剧增加。那么每一种猎物表型都有被至少一种捕食者攻击的危险。在这里，我们测试了具有高可塑性的猎物对两种捕食者中的任何一种的这种可变防御成本的后果。作为模式生物，我们将使用细菌猎物菌株恶臭假单胞菌，它可以形成不同的表型，即浮游细胞和生物膜。作为捕食者，我们将使用一个专门的浮游生物捕食者物种（四片草履虫，单一谱系）和一个专门的生物膜捕食者物种（棘阿米巴，单一谱系）。结合实验方法和数学模型，我们将利用两种捕食者物种的专业化来操纵捕食者群体内的性状变化。这影响到一个单一的猎物物种，为了保护自己免受一种或另一种类型的捕食者的攻击，它可以做出快速的表型可塑性反应，但不能同时对抗两种类型的捕食者。我们假设，捕食者群体的性状变异与猎物的表型可塑性的相互作用将导致捕食者和猎物各自的生物量和性状值的持续循环变化。这个微生物食物网的所有成员的非常短的世代时间将使我们能够观察许多代的时间序列，为两个相互关联的食物链内部和之间的长期相互作用和性状调整提供见解。此外，我们将建立一个先进的封闭系统和一个流动的恒化系统，在这个系统中，我们可以同时操纵防御成本和捕食者公会的特征变化。这些恒化系统将包括浮游生物栖息地和生物膜可以生长的可变数量的表面。它们可以通过不同的方式稀释浮游生物栖息地（猎物和捕食者）和生物膜栖息地（猎物和捕食者）来操纵损失率。为了将微生物种群动态与生态系统结构和功能联系起来，我们将研究捕食者群体（浮游生物和生物膜捕食者）的性状变化如何改变微生物食物网内的生物量分配和碳通量效率。据我们所知，迄今为止还没有进行过具有相应数学模型的此类实验。

Many ecological processes result from predator-prey interactions. Therefore, it is of considerable interest to investigate these interactions in order to gain a deeper understanding of ecosystem dynamics and functions. Several examples show that prey species can develop defended phenotypes to reduce predation and thus mortality. However, such defense mechanisms may come at considerable costs which pay off only in the presence of high predator densities, which may occur only temporally. Furthermore, costs of defense may dramatically increase if the prey is subject to predation by different predators and especially when defense traits are predator specific and incompatible. Then each prey phenotype is in danger to be attacked by at least one of the predators.Here we test the consequences of such variable costs of defense in a prey with high plasticity against either one of the two predators. As model organisms we will use the bacterial prey strain Pseudomonas putida, which can form contrasting phenotypes, i.e. planktonic cells and biofilms. As predators, we will use a specialized plankton predator species (Paramecium tetraurelia, a single lineage) and a specialized biofilm predator species (Acanthamoeba castellani, a single lineage). Combining experimental approaches with mathematical modeling we will employ the specialization of the two predator species to manipulate the trait variation within the predator guild. This affects a single prey species that can react with a fast phenotypic plasticity in order to defend itself against either one or the other type of predator but not both simultaneously. We postulate that this interaction of the trait variation of the predator guild together with the phenotypic plasticity of the prey will lead to ongoing cyclic changes in the respective predator and prey biomasses and trait values. The very short generation times of all members of this microbial food web will enable us to observe time series with many generations providing insights into long-term interactions and trait adjustments within and among two interrelated food chains. Further we will establish an advanced closed system and a flow-through chemostat system in which we can manipulate both, the costs of defense and the trait variation of the predator guild. These chemostat systems will comprise a planktonic habitat and a variable amount of surface on which biofilm can develop. They allow to manipulate the loss rates by diluting the plankton habitat (prey and predator) and the biofilm habitat (prey and predator) in separate ways. In order to link the microbial population dynamics to ecosystem structure and functions, we will investigate how the trait variation in the predator guild (plankton and biofilm predators) will change the biomass allocation and the carbon flux efficiency within the microbial food web. To our knowledge such experiments with a corresponding mathematical modelling have not been conducted so far.