Resource competition and interactive segregation between sympatric whitefish morphs

Two whitefish morphs have been identified in lakes in northern Norway from a bimodal distribution of gill raker numbers: a sparsely- and a densely-rakered. Habitat choice and feeding ecology of whitefish were studied in five lakes with the two morphs living in sympatry, and in five lakes harbouring only the sparsely-rakered morph. In sympatry, the two whitefish morphs exhibited a strict niche segregation, the sparsely-rakered morph mainly residing in the littoral zone feeding on zoobenthos, whereas the densely-rakered morph predominantly fed on zooplankton and dominated in the pelagic zone. In allopatry, however, the densely-rakered morph exhibited a larger niche width, utilising both the benthic and pelagic habitats and having a diet that included both zoobenthos and zooplankton. Thus, in sympatry with densely-rakered whitefish, the sparsely-rakered morph appears to be relegated from the pelagic zone, resulting in an interactive segregation due to resource competition between the two morphs.