Type of Document Dissertation Author Aresco, Matthew Joseph Author's Email Address email@example.com URN etd-03112005-153539 Title Ecological Relationships of Turtles in Northern Florida Lakes: A Study of Omnivory and the Structure of a Lake Food Web Degree Doctor of Philosophy Department Biological Science, Department of Advisory Committee
Advisor Name Title Frances C. James Committee Chair D. Bruce Means Committee Member Joseph Travis Committee Member Robert Deyle Committee Member Thomas Houpt Committee Member Thomas Miller Committee Member Keywords
- Pseudemys Floridana
- Food Web
- Trophic Structure
- Stable Isotopes
- Trachemys Scripta
- Apalone Ferox
Date of Defense 2005-02-28 Availability unrestricted AbstractLakes in the southeastern United States support a high diversity of reptiles and amphibians, including many species of turtles. Reptilian omnivores are abundant and their role in lake food webs must be important. In Leon County, Florida, I studied 17 lakes and the abundances of 3 species of turtles - yellow-bellied slider, Trachemys scripta, Florida cooter, Pseudemys floridana, and Florida softshell, Apalone ferox. I found that lakes in northern Florida range from low-nutrient, sand-bottom lakes to moderately eutrophic, muck-bottom lakes with abundant macrophytes, but one of the best predictors of turtle abundances was periphyton. Abundances of all three focal species were strongly correlated with a mud and muck substrate and both top-down (no alligator predation) and bottom-up (high periphyton productivity) factors. On a finer scale, abundances of the individual species were correlated with additional factors that may be related to trophic position: T. scripta – high phosphorus and high chironomid abundance, P. floridana – low macrophyte cover and high chironomid abundance, and A. ferox – high macroinvertebrate abundance, high snail abundance, and high phosphorus. An experiment revealed that intraspecific competition may be more important than interspecific
competition in partitioning resources between the omnivorous, T. scripta, and specialist algivore, P. floridana. In low resource environments, inefficient digestive physiology and intraspecific competition may limit density of an omnivore compared to that of a low trophic position specialist.
Stable isotope analysis of the entire food web of Lake Jackson, Leon County, Florida, revealed that filamentous macroalgae were the foundation of the web despite the much greater biomass of macrophytes. The turtle assemblage consisted of one herbivore and five omnivores. The diets of the three focal species differed: P. floridana was a specialist algivore (trophic position [TP] = 2.3), T. scripta was a generalist omnivore (TP = 3.3), and A. ferox was an omnivore with some specialization on insects and snails (TP = 3.8). There were few specialists (TP ³ 4.0) and few strict primary consumers. Omnivory was prevalent (90% of consumers), and the food web is one trophic level shorter than those in fish-dominated, north temperate lake webs that have few turtles, less species diversity, and lower productivity.
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