Variation in resource abundance affects diet and feeding morphology in the pumpkinseed sunfish (Lepomis gibbosus)

The pumpkinseed sunfish (Lepomis gibbosus Linnaeus; Centrarchidae) feeds extensively on molluscs, crushing them between its pharyngeal jaws. To address whether differences in mollusc availability might affect pumpkinseed diet and jaw morphology, we collected pumpkinseed from six Wisconsin lakes that varied in mollusc abundance and diversity. The percentage of molluscs in the diet increased directly with mollusc abundance. Moreover, there was a positive correlation between the mass of the pumpkinseed's main crushing muscle, the levator posterior, and the percentage of molluscs in the diet. These data support our previous work in two Michigan lakes showing that pumpkinseed pharyngeal jaws were more robust, and mollusc crushing performance improved, in a lake with higher mollusc densities. The combined Wisconsin and Michigan data exhibit a single relationship between levator posterior mass and percentage of molluscs eaten. Taken together, these studies demonstrate strong, functional relationships between prey availability, diet, morphology, and feeding performance, and suggest how morphology and feeding efficiency may evolve in response to variation in resource density.