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

本课题研究了特征变异性对捕食者-食饵系统动力学的影响。在DyaTrait的第一个资助期，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，其中捕食者协会的特征变异是通过表型可塑性(由同时具有浮游生物和生物膜表型的恶臭假单胞菌)实现的。通过添加不能捕食生物膜的选择性浮游生物摄食器(即纤毛虫草履虫)或不能摄食浮游生物的选择性生物膜摄食器(即阿米巴棘阿米巴)，可以操纵捕食者协会的特征变异性。一种新的恒化器系统已经成功开发，它允许分别选择性地操纵浮游生物和生物膜阶段，从而为研究浮游生物或生物膜摄食者防御放牧的成本提供了独特的机会。除了系统开发和参数确定外，我们在第一个资助期内重点研究了变化对浮游生物-生物膜耦合系统内生物量分配和动态的影响。在第二个资助期，我们的目标是检验四个高级假说，这四个假说得到了我们的数学模型的支持：1)捕食者协会的特征变化强烈地增加了整个系统的碳流，因为它避免了被防御的猎物表型的生物量的长期积累。2)猎物的表型可塑性可以驱动捕食者之间的间接促进和共存。第二个假设得到了我们的模型结果的支持，该模型预测了随着猎物被推向不可食用的浮游生物，单一捕食者群落中专门的生物膜捕食者将灭绝。3)第三，我们将重点关注系统动力学，以检验假设，即相等两种细菌表型的防御成本将导致系统的循环动力学。为了测试这一点，我们将同时控制浮游生物增长率(通过添加抗生素选择性减少)和生物膜增长率(选择性增强)，以平衡浮游生物和生物膜的生长。4)最后，我们将通过增加第二个具有增加生物膜增长率和减少浮游生物生长的猎物物种来增加系统的复杂性，从而允许由于表型可塑性和基因变异而产生的猎物协会的特征变异。我们将检验这一假说，即捕食者的特征变异增加了两个相互竞争的表型塑料猎物物种的共存范围。假说将通过恒化器实验和数学模型的紧密迭代来检验。它将与DyaTrait社区内的其他双营养系统以及共同核心小组密切联系。

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.