Piscivory is a strong structuring force in freshwater ecosystems and changes in environmental drivers acting on piscivore consumption rate should thus have strong impacts on food chain interactions, biodiversity and ecosystem functioning. In a future climate change scenario we expect to see increasing eutrophication and brownification of lake ecosystems. The associated increase in turbidity and/or change in watercolour will affect the optical environment for visually hunting predators and in this project we study the effects of such changes on piscivore-prey fish interactions.
In the laboratory, we quantify the effects of turbidity and water colour on reaction distance, prey choice and foraging rates of different piscivore species (northern pike, sander and perch) and their prey, the zooplanktivorous roach. We also study the effect of the optical environment on piscivore growth rates in lakes along a gradient of turbidity/water colour and in lakes before and after biomanipulation. Further, as turbidity and watercolour have a strong impact on piscivore consumption rate there should be a strong selection pressure for adaptive evolution of their visual system. Given the restricted gene flow among lakes we expect local adaptation of the visual systems in response to turbidity and watercolour. To test this we are studying morphology and physiology of the visual system of fish in lakes with different turbidity and watercolour.