PREY-SIZE RELATIONSHIPS AND FEEDING TACTICS OF PRIMITIVE STREAM-DWELLING DARTERS
Prey-size use and feeding tactics varied among three cooccurring darter species in the primitive subgenus Hadropterus (genus Percina). These darters span a wide range of body sizes, yet they all utilize the same lotic prey-size spectrum. An optimal-diet index (ODI) showed that small darters had more optimal diets than large darters. However, decelerating ODI curves showed that ontogenetic shifts occurred from number-maximizing to prey-size selective feeding tactics. Interspecific differences in feeding tactics, as characterized by differences in prey size, diet breadth, and numbers of prey, also were reflected by differences in slopes of ODI power curves. Percina nigrofasciata showed a relatively prey-size selective tactic; P. sciera showed a relatively number-maximizing tactic. In darters, prey-size selection corresponded with a broad diet and number maximizing corresponded with a narrow diet. When P. nigrofasciata were compared among four Black Creek sites, relatively optimal diets were found at two sites where large macroinvertebrates also were relatively abundant, as predicted from optimal foraging theory. However, only small differences in ODI values existed between two sites showing the greatest disparity in macroinvertebrate abundance. Prey size was an important diet characteristic related to the feeding tactics of particulate-feeding darters.