Graduation Year
2001
Document Type
Thesis
Degree
M.S.
Degree Name
Master of Science (M.S.)
Department
Biology
Degree Granting Department
Biology
Major Professor
Henry R. Mushinsky, Ph.D.
Co-Major Professor
Earl D. McCoy, Ph.D.
Committee Member
Phillip Motta, Ph.D.
Abstract
Food plant preferences of juvenile gopher tortoises, Gopherus polyphemus, were investigated in a west central Florida population. The juvenile gopher tortoises were free-ranging and were located in a sandhill habitat subject to yearly prescribed burns. Diet was determined by foraging observations, in which the number of bites taken per taxon, the number of plants sampled per taxon, and the amount of each taxon available along the foraging path were recorded. Preference was determined with Manly's alpha index of preference and Jacob's D electivity index. Selected plants in the habitat were analyzed for relative nitrogen content to investigate whether preferred plants contain higher amounts of nitrogen as an indicator of protein. Risk-proneness, measured as total distance traveled during foraging and as the farthest straight-line distance from the tortoise burrow, was tested for correlations with several variables: tortoise size, tortoise size category, percent of preferred plants along the foraging path, percent of foraging event spent under cover, speed. Daily activity patterns were investigated. Preferred plants contained significantly more nitrogen than avoided plants. Plant genera which were significantly preferred by juvenile gopher tortoises were: Richardia, Chamaecriste, Evolvulus, Ruellia, Dyschoriste, Polygala, Crotalaria, Liatris, Hedyotis, and "unidentified seedlings." No strong hierarchy, or degree of preference, of preferred plants could be determined. While the group of preferred plants, in general, contained greater amounts of nitrogen than the avoided plants, some of the preferred genera contained relatively little nitrogen. These plants may provide good sources of other nutrients important for growth and shell development, such as Ca. Speed and tortoise size category were the only variables correlated with risk-prone behavior. Larger individuals may be less vulnerable to predation, and individuals traveling farther distances may move faster to reduce exposure time. Juvenile gopher tortoises did not exhibit clear patterns in the time of day they perform specific activities, nor did they exhibit differences in the time of day of activity among seasons. They did, however, seem to follow a specific sequence of behavior regardless of when the behavior was initiated: emerge from the burrow, bask (thermoregulate), maintain the burrow, forage, re-enter burrow.
Scholar Commons Citation
Stilson, Terri Anne, "THE FORAGING ECOLOGY OF THE JUVENILE GOPHER TORTOISE, GOPHERUSPOL YPHEMUS" (2001). USF Tampa Graduate Theses and Dissertations.
https://digitalcommons.usf.edu/etd/8903
