Characterizing range-wide impacts of anthropogenic barriers on structural landscape connectivity for the Sonoran desert tortoise (Gopherus morafkai)

Context Linear anthropogenic barriers may reduce structural landscape connectivity for wildlife. Objectives Using graph-based connectivity indices, we modeled the potential impacts of linear barriers on structural connectivity and on individual patch importance at different biologically justified dispersal distance thresholds for the Sonoran desert tortoise, a wide-ranging species for which anthropogenic barriers may be reducing structural landscape connectivity. Methods To characterize the potential impacts of barriers on structural connectivity for the Sonoran desert tortoise, we compared network compartmentalization, individual habitat patch importance, and the spatial distribution of important habitat patches for models of structural connectivity reflecting the landscape prior to the development of linear barriers to models depicting current linear barriers in the landscape at different distance thresholds. Results Linear barriers fragmented the habitat patch network into a minimum of 239 patch components. Compartmentalization increased little as dispersal distance thresholds exceeded 10 km. In barrier simulations, patch importance mostly decreased and the spatial distribution of important patches shifted south. Conclusion Barriers are limiting structural connectivity for Sonoran desert tortoises and may prevent dispersal events, rescue effects in the event of localized extinctions, and successful range shift in response to climate change. Management efforts targeted at enhancing connectivity for ecological processes or movements occurring at 5–10 km may enhance the potential for longer-distance movements or generational dispersal occurring at a greater extent. Our methods provide an efficient framework for assessing changes in structural connectivity on a landscape extent that may be applied to addressing different problems or questions related to landscape connectivity.