Michael J. Dreslik
Abstract. The primary focus of this study was to ascertain the presence of sexual, seasonal, or ontogenetic differences in the diets of Trachemys scripta and Pseudemys concinna captured at Round Pond, Gallatin County, Illinois, between 17 May 1994 and 30 August 1995. I collected feces from T. scripta and P. concinna and separated the contents into eleven dietary categories for T. scripta and two for P. concinna. I quantified fecal volume by water cc displacement, then described each dietary category by frequency of occurrence, percent volume, and relative percent volume. Juvenile T. scripta fecal contents comprised >70% plant matter, while adult males and females had equal proportions of plant and animal matter in their feces. Percent volume and relative percent volume for T. scripta fecal samples did not differ between males and females, or between females and juveniles; however, I detected significant differences between males and juveniles and early (May-June) and late (July-August) samples. Overall the diversity of food items in the diet of T. scripta was large (Shannon index = 2.50) and the diversity of items expanded from early (Shannon index = 1.19) to late season (Shannon index = 2.72). Females consumed more mollusks than males, and males and females consumed more bryozoans than juveniles. I found Mollusks and bryozoans only in late season samples. Pseudemys concinna was herbivorous, specializing on epiphytic filamentous algae of the genera Cladophora and Oedogonium, with no differences in the frequencies of occurrence between males, females, and juveniles.
Illinois Natural History Survey, Center for Biodiversity, 607 East Peabody Drive, Champaign, IL 61820
