The ecological consequences of foraging boldness in juvenile bluegill sunfish (Lepomis macrochirus)

Biodiversity is manifest at all levels of ecological organization, from individuals to populations to communities, and elucidating the factors that generate and maintain this biodiversity is a central goal of ecology. Recently, there has been a surge of interest amongst behavioral ecologists to understand the degree to which individuals within a population differ in their behavioral types (often referred to as "animal personalities") and how this inter-individual behavioral variation is maintained. To date, most of the work on animal personalities has been conducted in the controlled environment of the laboratory. For my dissertation research, I studied the consequences of foraging boldness in juvenile bluegill sunfish (Lepomis macrochirus) using a combination of laboratory behavioral assays and experiments conducted in semi-natural ponds. Juvenile bluegill are a model system because they respond to tradeoffs in energy gain and predation risk, creating an ideal system to investigate consequences of individual differences in risk taking behaviors. A conflict between taking risks to acquire more energy and using refuge to avoid predators creates an ideal system to explore the consequences of inter-individual variation in foraging boldness. Chapter 1 reviews the evidence for behavioral variation in fish and focuses on the factors that can select for and maintain inter-individual variation in behavioral types within a population. In Chapter 2, I examined the behavioral structure, repeatability, and effect of social context on foraging boldness of juvenile bluegill under predation threat. I found that conspecific behavior and group composition affected the repeatability and foraging success of focal fish. Such group dynamics may increase the variability in observed behaviors, but it is important to recognize that individual behavioral types are likely a complex combination of responses to physiological and social cues along with genetic predisposition and lifetime learning. In Chapter 3, I determined the effects of boldness on growth, survival, and physiological investment into injury repair in a set of experiments in which juvenile bluegill were behaviorally assayed in the laboratory, individually marked, and then transferred to an experimental pond that mimics the environment of a natural lake. Bluegill that exhibited increased foraging under predation threat in the laboratory generally had higher growth rates in the field, but the magnitude of this effect was modified by ecological factors such as conspecific density and predator abundance. Surprisingly, there were no differences in survival based on boldness. However, shyer fish exhibited higher levels of fin regeneration, an indication that they invested more energy into injury repair. In Chapter 4, I examined the diets and associated habitat use of individual bluegill sampled from one of the pond experiments. I found that bolder individuals made greater use of the risky open-water habitat in the field and benefited by increasing their foraging gain. Additionally, bolder individuals showed higher use of pelagic habitats among fish that were at early stages of an ontogenetic niche shift. In Chapter 5, I highlighted the use of Passive Integrated Transponder (PIT) antenna systems as a tool for quantifying individual differences in habitat use, activity, and movement behaviors of aquatic organisms in field settings.