Stressor modulated community responses and functional redundancy of microbial predator-prey interactions
We address in particular Main Hypothesis 2 of the CRC, i.e., ecophysiological effects of multiple stressors on predator-prey interactions and related shifts of biodiversity (MH2). We focus on a crucial link in aquatic food webs, i.e. the effects of multiple stressors on grazing selectivity. The focus will be on protists feeding on bacteria but we will also address invertebrates grazing on protists. We hypothesise that the stressor-modulated specificity of predator-prey interactions might counter- balance species losses on the community level up to a certain critical level. We investigate i) whether multiple stressors have dominant, additive or interactive effects on biodiversity losses and ii) how critical levels of stressor-induced biodiversity losses affect food selectivity. We will use full factorial replicated time-series experiments to analyse effects between stressor treatments and control treatments during stressor application and after stressor release. In the AquaFlow systems, we will analyse community shifts of eukaryotes and bacteria based on amplicon data.
Further samples from the different time points will be used for protist food selection experiments using a proteobacterium, an actinobacterium and inert particles. Food selection will be determined using fluorescence in situ hybridization (FISH). Shifts in the food spectrum of macrozoobenthos organisms will be determined based on comparative analyses of gut contents vs. environmental food spectrum using amplicon data. Food selectivity will be calculated using Chessons alpha diversity index both for protists and for benthic invertebrates. Community composition and taxon diversity will be compared in the AquaFlow systems using amplicon sequencing (OTUs as proxy for taxon diversity). Shifts in community composition will be analysed between groups (classes/phyla) and within groups. Community analyses will test for differential effects of stressors on bacterial and eukaryotic microbial communities and further link findings from food selection experiments to community shifts, in particular for the target food organisms, i.e. Actinobacteria and Proteobacteria.