The influence of urbanization on the basking behavior of a Central Texas freshwater turtle community.
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Hill, Shannon K.
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Urbanization induced landscape modifications can dramatically alter riparian corridor dynamics and the composition of wildlife communities. Urbanized riparian corridors may alter or eliminate suitable freshwater turtle basking habitat by fragmenting shoreline vegetation, reducing basking substrates, and increasing the frequency of human disturbance. For this research, basking behaviors of the freshwater turtle community in the Brazos River (McLennan County, Texas) were observed from October 2004 to November 2007. The basking freshwater turtle community included the Texas river cooter, Pseudemys texana (Baur); red ear slider, Trachemys scripta elegans (Schoepff); Mississippi map turtle, Graptemys pseudogeographica kohni (Baur); Mississippi mud turtle, Kinosternon subrubrum hippocrepis (Gray); smooth softshell, Trionyx muticus muticus (Le Sueur); and spiny softshell, Trionyx spiniferus pallidus (Webb). Turtle community composition, basking site attributes, and the intensity of shoreline urbanization were measured for each observation of a basking turtle. Results showed that the community of basking freshwater turtles was moderately diverse with an endemic, P. texana, as the most abundant species. Abundances of basking P. texana were greater where potential basking sites were abundant. The number of potential basking sites and a basking site’s distance from shoreline facilitated greater basking abundances of T. scripta. All species preferentially basked alone. In cases of multiple occupancy on a single site, P. texana and T. scripta basked indescriminantly relative to the species present on the basking site. Basking site size and orientation contributed to cases of multiple occupancy. Responses to basking site attributes and social dynamics varied widely across taxa. Four indices of shoreline urbanization at three spatial scales were used to assess the relationship between urbanization and basking turtle behavior. Indices included local-scale Shoreline Modification and Disturbance Frequency, broad-scale Building Density, and reach-scale Human Density. At the local scale, abundances of basking turtles were greatest in areas of high Shoreline Modification characterized by a substantial reduction in woody shoreline vegetation. Also at the local scale, Disturbance Frequency of human intrusion limited basking turtle abundance in areas of daily disturbance. Most basking turtle species tolerated, and may have actively selected basking sites in areas of relatively high levels of localized urbanization.