Character Displacement and Habitat Shift in a Native Cisco in Southeastern Lake Michigan: Evidence for Competition?

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Abstract
The decline of several planktivorous fish in Lake Michigan following the invasion of alewife (Alosa pseudoharangus) has often been attributed to competition for zooplankton. Shifts in resource use or trophic morphology by native fish have not been well documented. In the 19 yr following the increase of alewife, gill rakers of a native cisco, bloater (Coregonus hoyi), from southeastern Lake Michigan were significantly reduced both in number (by 2.1) and length (by 15%). Bloaters now shift to bottom habitats and benthic prey as much as 2 yr earlier in their life history than before alewife became abundant. Though the causal factors for these shifts are difficult to document, the idea that they are due to selection for benthic foraging efficiency in response to alewife competition is favored by the existing data.

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