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Latitudinal Variation in the Thermal Biology of Ornate Box Turtles
Lisa R. Ellner and William H. Karasov
Vol. 1993, No. 2 (May 3, 1993), pp. 447-455
Stable URL: http://www.jstor.org/stable/1447144
Page Count: 9
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We compare the thermoregulatory behavior of ornate box turtles (Terrapene ornata) from a northern population in Wisconsin with published information about a southern population in Kansas. In a laboratory thermal gradient, body temperature ( T b) of Wisconsin turtles (23.5 ± 1.3 C SE) averaged 6.3 C lower than reported for the same species from Kansas. T b of free-living turtles in Wisconsin (measured with temperature-sensitive transmitters) averaged 4.0 C lower than T b of Kansas turtles when the turtles were basking, moving, or seeking thermal protection in burrows from high temperatures. Using field measures of operative environmental temperature ( T e; measured with hollow copper models), we deduce (1) that the lower field T b of Wisconsin turtles reflects active selection of lower T b and is not simply a passive result of a lower environmental heat load; and (2) that behavioral selection by Wisconsin turtles of a lower and broader range of T b increases potential daily activity time.