Bottlenose dolphins (Tursiops truncatus) are large apex carnivores that often live in close proximity to metropolitan areas. As a result, they experience disturbances such as habitat alteration, competition with humans for food resources, and anthropogenic injury and mortality. Understanding variation in foraging habits of bottlenose dolphins over time and within populations reflects how these predators use and respond to changes in habitat and prey availability. Stable isotope analysis provides powerful insight into the foraging habitat and tropic level (foraging habits) of top predators. Carbon isotope values (δ13C) differentiate between seagrass (c.a. 12 ‰) and nonseagrass (phytoplankton and mangrove, < -15 ‰) based food webs in coastal estuaries and nitrogen isotope values (δ15N) increase with trophic level. I evaluated temporal, demographic and individual variation in the foraging habits of bottlenose dolphins resident to Sarasota Bay, Florida, using stable isotope analysis.Chapter one examines bottlenose dolphin response to a series of disturbances. From 1991 to 2010, bottlenose dolphin showed a significant decrease in δ13C values and a significant increase in δ15N values, trends likely related to changes in habitat use after a 1995 commercial net fishing ban. Across a larger time period, bottlenose dolphin δ15N values significantly increased from 1944 to 1990, then data became variable. This is likely related to an initial increase and subsequent decline in anthropogenic nitrogen loading to Sarasota Bay which contributes 15N enriched nitrogen to the system. These data suggest that environmental legislation is effective in remediating anthropogenic nutrient excess in food webs. The second chapter examines the foraging habits of three demographic groups: male, female and juvenile bottlenose dolphins. Isotope values of common bottlenose dolphin prey fish were used to inform a Bayesian mass-balance model to estimate the abundance of certain groups to the diet of males, females, and juveniles. Low trophic level, seagrass associated prey are important for all demographic groups. Bayesian standard ellipses identified the degree of variability in foraging habits. The ellipse center identifies the mean isotope value for a demographic group and the ellipse size and shape determined from a covariance matrix indicates the degree of variation in the demographic group's foraging habits. While males show relatively low variability, the female standard ellipse indicates large variability in foraging habitat and trophic level.Female bottlenose dolphin foraging habits are examined further in chapter three, which investigates individual specialization. Individual specialization results from each individual using a subset of the resources used by the population. Multiple chronological isotope samples from the same individual allow the partitioning of isotopic variation (total niche width, TNW) into a within individual component (WIC, high in generalists) and a between individual component (BIC, high in individual specialists). Isotope analysis of sequential growth layers from teeth indicate that BIC constitutes 60% of TNW for δ15N and 88% of TNW for δ13C, indicative of a large degree of individual specialization. The incidence of individual specialization likely results from processes associated with learning, social structure, and intraspecific competition.
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