Emergent aquatic insects are elemental in linking streams with surrounding terrestrial food webs, by providing valuable nutrients to riparian predators. However, the presence of chemical pollution in streams may alter this connection and indirectly affect the terrestrial ecosystem. Previous studies have found changes in riparian food webs near streams polluted with pesticides and waste water, but the mechanisms behind this have not been fully investigated.

The ongoing food web ecology project is studying how anthropogenic stressors in streams indirectly affect the diet and behaviour of terrestrial predators. To achieve this, we performed a field study on two riparian insectivores, bats and spiders, at 16 stream sites in 2020. The sites were similar in natural structure of the streams, but differed in exposure to chemical pollution, as they were either upstream or downstream of agricultural and urban landscapes. At each site, bat calls were recorded to measure the abundance of different species and their feeding attempts. Spiders were also collected to characterize the contribution of aquatic subsidies to their diets, using DNA metabarcoding. We also measured pesticides and waste water markers at each study site, and sampled emerging insects from the streams. The spider diet analyses and further field sample analyses will be conducted in 2021-22.

Due to the direct effects of chemical pollution on emergent aquatic insects, we expect a negative response in the diets and behaviour of predators at sites with more pollution. For example, polluted streams may have lower bat abundance with fewer hunting calls, and the contribution of aquatic subsidies to spider diets could also decrease. These effects may also differ for generalist versus specialist predators. By combining the information from this study with other Systemlink projects, we can better understand how the effects of anthropogenic stressors in streams propagate to and change the riparian ecosystem.

Maike Huszarik

Martin Entling

2019-2023

Deutsche Forschungsgemeinschaft/German Research Foundation (DFG)

Peter Hambäck, University of Stockholm

SystemLink

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Trophic interactions (or food webs), anthropogenic stressors; chemical pollutants, forested streams; bats, spiders; Germany, Rhineland-Palatinate