The behavioural response of juvenile bluegill sunfish (Lepomis macrochirus ) to predation risk when selecting between patches of artificial vegetation differing in food and stem density was investigated. Bluegill foraging activity was significantly affected by all three factors. Regardless of patch stem density or risk of predation bluegills preferred patches with the highest prey number. During each trial bluegill foraging activity was clearly divided into a between‐ and within‐patch component. In the presence of a predator bluegills reduced their between‐patch foraging activity by an equivalent amount regardless of patch stem density or food level, apparently showing a risk‐adjusting behavioural response to predation risk. Within patches, however, foraging activity was affected by both food level and patch stem density. When foraging in a patch offering a refuge from predation, the presence of a predator had no effect on bluegill foraging activity within this patch. However, if foraging in a patch with only limited refuge potential, bluegill foraging activity was reduced significantly in the presence of a predator. Further, this reduction was significantly greater if the patch contained a low versus a high food level, indicating a risk‐balancing response to predation with respect to within‐patch foraging activity. Both these responses differ from the risk‐avoidance response to predation demonstrated by juvenile bluegills when selecting among habitats. Therefore, our results demonstrate the flexibility of juvenile bluegill foraging behaviour.
Bluegills (3.2–4.7 cm, SL) and largemouth bass (Micropterus salmoides) (25–40 cm, SL) were collected from Lake Opinicon, Ontario, Canada (40° 30' N 76° 30' W). Fish were housed in the laboratory at Queen's University, Kingston, Ontario, at 20–25°C, and a light regime of 12 h L: 12 h D. Bluegills were maintained on a diet of frozen brine shrimp, while bass were fed pieces of frozen fish supplemented with live bluegills. Largemouth bass are a natural predator of bluegills within the size range used in this study.