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UBC Theses and Dissertations

Effective sampling and detecting biogeographic trends of the painted turtle, Chrysemys picta. Tesche, Melissa Rose


Nearly half of the world’s turtle species are endangered or threatened with extinction. Conservation efforts need effective sampling programs that provide high quality life history and population parameters on which to base management decisions. These parameters vary from one population to the next, as well as across a species’ geographic range, and local variation can be high. In this thesis, I investigate conventional trapping methodologies and examine potential biogeographical trends in body size and degree of sexual dimorphism in the painted turtle, Chrysemys picta. Painted turtles in the Okanagan valley of British Columbia, Canada, are nationally listed as Special Concern. Using hoop nets, basking traps, and dip nets, I sampled 13 ponds representing the range of occupied habitats in the valley. My results demonstrate that combining all three trap methods resulted in the highest recapture rates and more precise population estimates than single trap methods alone. Overall, hatchlings and juveniles were best caught by dip netting, and hoop traps performed the worst for adults of both sexes. Capture success of each trap method was not consistent across ponds, and each trap method performed poorly in at least one pond, pointing to the need to combine trap methods to get the most representative sample possible. My thesis research strongly suggests that combining conventional turtle trapping methods in a sampling program can provide stronger inference than a single method alone. I assessed the average body size and the degree of sexual size dimorphism for the turtles at each pond. Painted turtles in the Okanagan are bigger than their southern conspecifics, supporting Bergmann’s rule which asserts an inverse relationship between temperature and body size. There was no trend between latitude and degree of dimorphism. My work shows that local variation in biogeographic analyses suggests previously published biogeographic trends for C. picta may not be accurate. More research on the causes of local variation in size and growth rate will be valuable in the efforts to protect this and other turtle species in British Columbia.

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