Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Department

Biology

First Advisor's Name

Dr. Michael Heithaus

First Advisor's Committee Title

Executive Director of School of Environment, Arts and Society; Associate Dean of College of Arts & Sciences; Professor

Date of Defense

3-19-2014

Abstract

Top predators serve important roles within their respective ecosystem through top-down and bottom-up effects, yet understanding how these roles vary among individuals within predator populations is still in its early stages. Such individuality can have important implications for the functional roles predators play within their respective ecosystems. Therefore, elucidating the factors that drive persistent individual differences within populations is crucial for understanding how individuals, and in turn populations, will respond to environmental changes and anthropogenic stressors, and the implications of these responses for particular ecological functions. In this dissertation I investigated the movements, residency patterns, and trophic interactions of a juvenile bull shark (Carcharhinus leucas) population in a coastal estuary that serves as a nursery. I found that bull sharks undergo ontogenetic niche shifts in their diets and habitat use, with a gradual shift from using freshwater and estuarine resources to marine resources as sharks grew. This behavioral shift appeared to be driven by age-based differences in tradeoffs between safety from predators and availability of prey. Nested within population-level trends in behavior, there was considerable, and consistent, individual variation in both movements and trophic interactions suggesting individual specialization and divergent behavioral tactics within the population. Different behavioral types likely play different roles in food web connectivity and ecosystem dynamics, thus understanding the drivers and importance of phenotypic variability among species will be crucial for improving management strategies and predicting the responses of species and ecosystems to impending changes in environmental conditions and human impacts.

Identifier

FI14040852

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