Thursday, August 5, 2010
Exhibit Hall A, David L Lawrence Convention Center
Background/Question/Methods A tradeoff between increased foraging activity and predation risk may maintain behavioral variation within a population. However, little is known about whether individual behaviors are consistent or if individuals show plasticity in various contexts. We used bluegill sunfish (Lepomis machrochirus) to test whether exposure to predators solicited plastic responses in foraging behavior. We stocked 100 yearling bluegill into nine 1,000 L cattle tanks and applied one of three predation treatments using largemouth bass (Micropterus salmoides) as predators: control, predation threat, and unrestricted predator. Treatments had no predators, caged predators, and free-roaming predators, respectively. After exposure to predation treatments, surviving bluegill were acclimated to a laboratory setting and assayed for various foraging behaviors in the presence of a caged bass. Behaviors were summarized using Principle Components Analysis. Bluegill from the behavioral assays were given individual marks and then stocked into a pond partitioned by netting into quadrants with or without predators (bass). After two months, we drained the pond to identify all remaining bluegill and to relate their growth and survival to boldness scores from the laboratory assays.
Results/Conclusions Bluegill exposed to caged predators in the cattle tanks (predation threat treatment) were bolder when assayed in the laboratory foraging trials than bluegill from either the control or unrestricted predation treatments. These results suggest that there is plasticity in behavior. Bluegill may have learned that the caged predator was not a threat and displayed bolder behavior in the foraging assay. Bluegill from the control (no predator) cattle tanks may have been less bold during the laboratory assays because the caged bass was a novel threat. Results from the pond experiment were confounded due to movement of fish between quadrants following muskrat damage to the partitions. However, bluegill collected from the quadrant without bass had equal survivorship among bold and shy behaviors, but bold fish grew faster. In the quadrant with a predator, bold fish did not survive as well as shy, but shy fish grew more than bold fish. The decreased survival of bold fish is consistent with the foraging activity-predation risk tradeoff. Differences in growth and survival show that population dynamics are influenced by variation in individual foraging behavior. Although intraspecific behavioral variation may be maintained through this tradeoff, the importance of plasticity has yet to be resolved.
Results/Conclusions Bluegill exposed to caged predators in the cattle tanks (predation threat treatment) were bolder when assayed in the laboratory foraging trials than bluegill from either the control or unrestricted predation treatments. These results suggest that there is plasticity in behavior. Bluegill may have learned that the caged predator was not a threat and displayed bolder behavior in the foraging assay. Bluegill from the control (no predator) cattle tanks may have been less bold during the laboratory assays because the caged bass was a novel threat. Results from the pond experiment were confounded due to movement of fish between quadrants following muskrat damage to the partitions. However, bluegill collected from the quadrant without bass had equal survivorship among bold and shy behaviors, but bold fish grew faster. In the quadrant with a predator, bold fish did not survive as well as shy, but shy fish grew more than bold fish. The decreased survival of bold fish is consistent with the foraging activity-predation risk tradeoff. Differences in growth and survival show that population dynamics are influenced by variation in individual foraging behavior. Although intraspecific behavioral variation may be maintained through this tradeoff, the importance of plasticity has yet to be resolved.
