| Agassiz's desert tortoise populations are exposed to a variety of anthropogenic threats that vary in nature, severity, and frequency. Tortoise management in conservation areas can be compromised when the relative importance of these threats is not well understood. We used HexSim to develop simulation models for desert tortoise populations occupying two study areas in the western-central (Superior Cronese) and the eastern (Gold Butte-Pakoon) Mojave Desert, each with a distinct set of site-specific threats. We parameterized threats models from published sources of information, and conducted independent simulations of threats at varying levels of severity. We subjected modeled tortoise populations to simulations of threats associated with human presence and subsidized predators. Additional simulated threats in the Superior Cronese region included disease and habitat degradation on land in-holdings, whereas Gold Butte-Pakoon modeled tortoise populations were exposed to simulations of wildfire, livestock grazing, and feral burros. We used our study area-specific simulation models to rank the threats' relative importance to population viability. We found that threats more widely distributed in time and space significantly limited tortoise population growth more than threats that were patchily distributed or temporally dynamic, allowing us to provide site-specific management recommendations that accounted for the relative effects of the threats. |