Is ecological segregation in a pair of sympatric coregonines supported by divergent feeding efficiencies?

Some of the sympatric species pairs commonly described in temperate freshwater fishes provide evidence for ecological specialization driven by competition for food resources as a potential prerequisite of subsequent sympatric speciation. In the postglacial Lake Stechlin (Germany), two sympatric coregonines coexist, common vendace ( Coregonus albula ) and endemic dwarf-sized Fontane cisco ( Coregonus fontanae ). The species segregate vertically along the light intensity and prey density gradients of their pelagic environment. Accordingly, we hypothesized that the species might show differences in their foraging efficiency associated with these environmental gradients. We investigated the feeding behaviour by measuring the functional response of both species to Daphnia magna at various prey densities (0.25–8 individuals·L–1) and light intensities (0.005–5 lx) at a deep blue light spectrum to simulate their natural habitat. Decreasing light intensity and prey density significantly depressed consumption rates in both species. Overall, we observed only weak differences in feeding behaviour, which indicates that the species are functionally similar, coexisting planktivores.