Biology Ph.D. Dissertations

Conservation of the Spotted Turtle (Clemmys guttata): Identifying Critical Demographic and Environmental Constraints Affecting Viability

Date of Award

2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Biological Sciences

First Advisor

Karen Root

Second Advisor

Juan Bouzat (Committee Member)

Third Advisor

Enrique Gomezdelcampo (Committee Member)

Fourth Advisor

Helen Michaels (Committee Member)

Fifth Advisor

Candace Archer (Committee Member)

Abstract

The Spotted Turtle, Clemmys guttata, is a freshwater turtle species currently protected throughout most of its range. Urgent conservation action is warranted to assess population viability and to focus management for this species. This body of work is premised on four overarching questions which addressed the population viability, current population status, critical environmental variables, and management strategies. We performed sensitivity analyses utilizing demographic data from the literature incorporated into an age-based population model. We conducted a mark-recapture study at two study sites in the Oak Openings Region of northwest Ohio to assess the habitat and population characteristics of Spotted Turtles. We used presence and absence locations to identify critical environmental variables at the local and landscape scales, resulting in a habitat suitability model. Our sensitivity analyses identified the variables most influential to Spotted Turtle viability (i.e., survival rates of older age classes, population size, and age at reproduction). We found that Spotted Turtle density was higher than those reported in recent literature and that age structure was not as adult biased as many other populations. In general, turtles were using areas within sites that had higher water and taller, denser ground vegetation. At the local scale, turtle presence could be explained by low slope, higher levels of June moisture, and intermediate levels of March brightness. At the landscape scale annual solar radiation, June brightness, land cover, June NDVI, and slope were significant in explaining turtle presence. A habitat suitability map was created to locate other potentially suitable areas within the Oak Openings Region. Based on these results, the variables found to influence Spotted Turtle population persistence over time should be the focus of future field work and monitoring throughout the range. Local management should focus on managing current sites since Spotted Turtles show high site fidelity, but also to acquire additional lands since potential habitat makes up less than 1% of the region. We have shown that Spotted Turtles have complex habitat requirements, making it important to have a multiscale view which considers the context of different environmental variables that accommodate the year round requirements for turtle viability.

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