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Human behavior is an important factor in understanding the impact of exurban sprawl (i.e. low-density rural home development) on native species. We studied the long-term effect of pet collection on populations of the threatened spur-thighed tortoise by residents of exurban areas in southeastern Spain. We built a system dynamic model using authors’ own data and bibliographic data about tortoise population dynamics, the housing development dynamics, and the behavior of local residents toward this species. The model includes two submodels (spur-thighed population dynamics and households dynamics) interconnected through a tortoise collection submodel. Simulations showed that exurban intensity (i.e. size of a housing development) is essential in determining the intensity and speed of tortoise population decrease. Populations may become extinct due to collection in areas around medium to large housing developments (above 650 houses). Low housing development causes a considerable reduction of original population levels (more than 14%). Environmental education program by itself, with the aim of reducing the willingness of new residents to keep tortoises in captivity, does not seem very effective. The quality and the speed with which the educational program is initialized are key factors in determining the effectiveness of the educational program. The scenarios simulation results suggest that the integration of policies of strong development constraints and educational programs are the most effective way in reducing the impact of exurban development on tortoise populations. (c) 2012 Elsevier B.V. All rights reserved.