Apparent Size as the Determinant of Prey Selection by Bluegill Sunfish (Lepomis Macrochirus)

Abstract

Abstract.Although it is known that visual predation by planktivorous fish tends to be size selective, the mechanism by which fish select their prey has not previously been described.Experiments in which bluegill sunfish (Lepomis macrochirus) were given a binary choice be tween prey of different sizes presented at different distances showed the fish selected the prey that appeared largest, either because of its actual size or its proximity to the fish. This paper incorporates this mechanism of prey selection by apparent size into a model of bluegill predation. According to the model, bluegill, in choosing the apparently largest prey under all conditions, alter their diet composition depending upon the abundance of prey. When prey are abundant, bluegill predominantly select prey of the largest size class available because these have the greatest probability of appearing largest; as large prey become scarce and smaller prey have a greater chance of appearing large, the fish tend to eat more prey from smaller size classes. When the model is tested against data from published fish-feeding ex periments, the predicted size ratios of prey eaten correlate accurately with the observed ratios and numbers of prey eaten.

Shared Preferences by Predators and Females for Male Ornaments in Swordtails

“…Theory makes diametrically opposed predictions about how predators should respond to novel, conspicuous prey. By definition, more conspicuous prey are more likely to be detected, which could increase predation rate (Curio 1976;O'Brien et al 1976). Alternatively, novel phenotypes may be at lower risk of predation.…”

“…Predators are often size selective, preferring larger prey (Wilbur 1988), although there are few studies addressing the basis of this preference. In one case, bluegill sunfish preferred daphnia of larger apparent size (independent of actual size; O'Brien et al 1976). These factors suggest that visual predators of swordtails may share with their prey an ancient preference for large size, manifesting itself as a bias for both large males and males with swords.…”

Differences in feeding selectivity and efficiency between young-of-the-year European perch (Perca fluviatilis) and roach (Rutilus rutilus) — field observations and laboratory experiments on the importance of prey movement apparency vs. evasiveness

“…Therefore not surprisingly, prey visibility (Zaret & Kerfoot 1975) or apparent size (O'Brien et al 1976) determines fish selection more significantly than actual prey size (Brooks & Dodson 1965). Moreover, recent experiments with virtual plankton images (Brewer & Coughlin 1996) show that fish select accordingly to the moving pattern of the prey and so prey motion can increase prey conspicuousness to fish predators as has been suggested by Zaret (1980).…”

Pipefish foraging: effects of fish size, prey size and altered habitat complexity

“…Mechanistic foraging models that account for visual reactive field volumes (Werner & Hall 1974), prey visibility (Zaret & Kerfoot 1975), prey motion (Zaret 1980a) and the apparent size of prey (O'Brien et al 1976) have been developed for zooplanktivorous fish. Similar models which account for the visual and physical inhibitory effects of vegetation or other structures have yet to be developed.…”