Recently, ecologists have found that a tradeoff between increased foraging activity and predation risk may lead to behavioral variation within a population, with individuals showing consistent, repeatable responses to foraging tradeoffs. Most of the work on this subject has been conducted in the laboratory, where behavioral traits are most easily quantified. It is now necessary to determine how these tradeoffs may affect population dynamics and ecological interactions in the field. To apply the concepts of this foraging gain-predation risk tradeoff in the field, we first assayed young-of-year bluegill (Lepomis machrochirus) in the laboratory and then differentially marked individuals classified as bold or shy foragers. These marked fish (200 bold, 200 shy) were then stocked into a pond at the Kellogg Biological Station’s Experimental Pond Facility, along with their natural predator, the largemouth bass (Micropterus salmoides). After two months, we drained the pond to collect all remaining individuals, measuring survivorship and growth. Our hypothesis was that “bold” foragers would have a higher growth rate but lower survival than “shy” foragers in the presence of a predator. Physiological variables were also quantified to examine how foraging behavior may affect somatic growth efficiency and injury repair.
Results/Conclusions
After draining the ponds, we found that more shy fish survived predation than bold fish (66 bold, 74 shy recovered). There was also a significant difference in the size distributions of bold and shy fish found at the end of the experiment (length p=0.01, weight p=<0.001 Mann-Whitney U-Test), with bold fish averaging 68.6±0.08 mm standard length and shy fish averaging 65.6±0.08 mm standard length). Interestingly, shy fish showed a significantly greater extent of fin regrowth during the course of the experiment, suggesting that they allocate more energy to repair. However, there was no difference in average scale strength between the two behavioral groups. Our data supports the prediction that a predation risk/foraging gain tradeoff accompanies the behavioral differences between shy and bold foragers, and that bold fish may take more risks to achieve faster growth at the expense of higher mortality. Further work is needed to test this tradeoff and its consequences for survival, growth, and population dynamics of natural populations, as well as to determine how the costs and benefits of shy and bold behaviors may affect fitness costs and potentially allow both behavioral types to be successful within a population.
