Abstract
Predators affect prey and non-prey communities through consumptive effects (CE) and non-consumptive effects (NCE), with consequences for ecosystem functions. Aquatic sediments are entanglements of particles that house diverse communities of microbes and invertebrates involved in ecosystem functions. In this study, we used experimental sediment cores as microcosms to explore the effects of two predatory flatworm species: Polycelis tenuis and Planaria torva. Flatworms secrete mucus for locomotion. Their motility results in particle displacement, which in turn increases the local availability of labile compounds. In this study we asked: (1) How do predators affect biomass allocation in a comprehensive community? (2) What is the impact of these effects on ecosystem functions? Our results showed that flatworms increased the sediment reworking rate and affected the packaging of biomass in prey (e.g., oligochaetes) and non-prey (e.g., protozoa) organisms through both CE and NCE. Causal links between community structure and ecosystem functions suggested different pathways of predator control: Polycelis indirectly influenced P availability, which increased the biomass of bacteria and protozoa, whereas Planaria elicited a trophic cascade and had a wider ranging diet than Polycelis. Our results support the use of flatworms as models to link the functions of organisms with those of ecosystems.
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