A Complex Foraging Polymorphism in a Multi-niched Habitat as Demonstrated by Differences in Foraging Efficiencies in Lepomis Macrochirus (The Bluegill Sunfish)
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The Bluegill Sunfish, Leoomts macrochlrus, is capable of exploiting. two distinct niches within one lake, the openwater, or limnetic, and the vegetation, or llttoral. The demands of these two environments in terms of foraging are very different. It follows that natural selection is working on this species in two distinct, perhaps conflicting, directions. The possibility that this type of selective pressure results in a complex foraging polymorphism in the population is studied in this experiment. Bluegills were captured from each part of the lake. Fourteen of these were kept in the laboratory and given feeding trials to determine their efficiencies as foragers in artificial vegetation. The mean times per capture and number of hovers between captures at five levels of prey depletion were determined for all fish. Both of these values were higher for fish captured in the openwater. A two-way analysis of variance showed that both variables, habitat and depletion level, influenced foraging success. There was significant interaction between these variables. Each fish was measured for specific morphological characteristics. A Canonical Discriminant Function was constructed using morphological measurements from a large sample of fish captured on the same day as the experimental fish and used to classify the test fish as either a vegetation forager or openwater forager. A significant negative correlation was found between individual Canonical scores and mean capture times and hover efficiencies at high levels of prey depletion. Vegetation foragers required significantly less time to find prey than did openwater foragers. This evidence supports the hypothesis that a complex foraging polymorphism exists in the population studied.
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