Biotic interactions

Our studies underlined how responses to stressors increase and release are modified by biotic interactions. Competition, but also other biotic interactions such as parasitism and predation, shape communities and are supposed to be of particular importance in recovery phases, e.g. through community closure. Various experiments and field studies have been performed on biotic interactions. We found that:

• Salinity affects the food selection of bacterivorous flagellates and therefore changes the relative grazing pressure on different bacterial phyla (see Boden et al., 2023).
• Carbon-based isotope analysis of amino acids revealed parasite (cestode) nutrient assimilation closely linked to the liver metabolism of the fish host (three-spined stickleback). Additionally, increased amino acid fractionation in infected sticklebacks suggested increased (immune-) metabolic activities due to parasitic infection (see Hesse et al., 2023).
• Several macroinvertebrate species respond to chemical cues associated with fish predation by going into the drift. When exposed to anthropogenic stressors, this reaction to fish predators was suppressed.
• Different groups of parasites (e.g., Microsporidia, Monogenea, Trematoda, Cestoda, Acanthocephala, and Nematoda) modulate the response of their hosts to stressors (see Grabner et al., 2023), while at the same time stressor effects lead to a global decline of parasites with complex life cycles (see Sures et al., 2023).