Trait variability and defense costs in coupled bi-trophic plankton - biofilm systems: effects on predator-prey dynamics and coexistence

本项目研究了特征变异性对捕食-被捕食系统动力学的影响。在DynaTrait的第一个资助期内，我们建立了一个实验浮游生物-生物膜系统和相应的数学模型框架，其中猎物公会的性状变异是通过表型可塑性实现的（通过具有浮游生物和生物膜表型的细菌恶臭假单胞菌）。可以通过添加不能以生物膜为食的选择性浮游生物食饵（即，纤毛虫草履虫（Parameciumtetraurelia））或不能以浮游生物为食的选择性生物膜摄食者（即，卡氏变形虫（amoeacrylamoeacrylcastellanii）。一种新的恒化器系统已经开发成功，它允许选择性地操纵浮游生物和生物膜相分开，从而提供了独特的机会，调查防御放牧的成本由浮游生物或生物膜饲养。除了系统开发和参数确定，我们集中在第一个资金周期内的变化对生物量的分配和动态的影响耦合的生物膜系统。在第二个资助期内，我们的目标是测试四个先进的假设，这些假设得到了我们的数学模型的支持： 捕食者公会中的性状变异强烈地增加了整个系统的碳流，因为它避免了生物量在被防御的猎物表型中的长期积累。 猎物的表型可塑性可以间接促进捕食者之间的共存。第二个假设得到了我们模型结果的支持，它预测了在单一捕食者群落中，随着猎物被推向不可食用的捕食者，专门的生物膜饲养者将灭绝。 第三，我们将集中在系统动力学测试的假设，均衡的防御成本为两种细菌表型将导致系统的循环动力学。为了测试这一点，我们将操纵浮游生物生长速率（通过抗生素添加选择性减少）和生物膜生长速率（选择性增强），以平衡浮游生物和生物膜的生长。 最后，我们将增加系统的复杂性，增加生物膜的生长速率和减少浮游生物的生长，从而允许性状变异的猎物公会产生的表型可塑性和基因型变异的第二个猎物物种。我们将测试的假设，在捕食者的性状变化增加的范围内共存的两个竞争的表型塑料猎物物种。假设将在密切迭代与恒化器实验和数学建模进行测试。它将与DynaTrait社区内的其他双营养系统和共同核心组密切相关。

The present project investigates the effect of trait variability on the dynamics of predator-prey systems. During the first funding period of DynaTrait, we established an experimental plankton – biofilm system and a corresponding mathematical model framework, in which trait variability in the prey guild is realized by phenotypic plasticity (by the bacterium Pseudomonas putida with both plankton and biofilm phenotypes). Trait variability in the predator guild can be manipulated by adding either a selective plankton feeder being not able to feed on biofilms (i.e., the ciliate Paramecium tetraurelia) or a selective biofilm feeder being not able to feed on plankton (i.e., the amoebae Acanthamoebae castellanii). A novel chemostat system has been developed successfully, which allows selective manipulation of both the plankton and the biofilm phase separately and which thus offers the unique opportunity to investigate the costs of defense against grazing by either plankton or biofilm feeders. Besides system development and parameter determination, we focused within the first funding period on the effects of variation on biomass allocation and dynamics within the coupled plankton-biofilm systems. In the second funding period, we aim to test four advanced hypotheses, which were supported by our mathematical modelling:1) Trait variation in the predator guild strongly increases the carbon flow of the total system because it avoids long-term accumulation of biomass in a defended prey phenotype.2) Phenotypic plasticity in prey can drive indirect facilitation and coexistence between predators. The second hypothesis is supported by our model results, which predicts extinction of the specialized biofilm feeders in single-predator communities as the prey is pushed towards non-edible plankton.3) Third, we will focus on the system dynamics in testing the hypothesis that equalizing the costs of defense for each of the two bacteria phenotypes will lead to cycling dynamics of the system. To test this, we will manipulate both the plankton growth rates (selective reduction by antibiotic addition) and biofilm growth rate (selective enhancement) in order to equalized plankton and biofilm growth.4) Finally, we will add complexity to the system by adding a second prey species with increasing biofilm growth rates and decreasing plankton growth and thus allow trait variation in the prey guild generated by both phenotypic plasticity and genotypic variation. We will test the hypothesized that trait variation in predators increases the range of coexistence of two competing phenotypically plastic prey species.The hypotheses will be tested in close iteration with chemostat experiment and mathematical modelling. It will be closely linked to other bi-trophic systems within the DynaTrait community and to the common core group.