Responses of common chuckwallas and their food plants to increasing aridity

Desert regions are becoming both warmer and more arid, potentially challenging the ability of even arid-adapted species to exist within their current ranges. Here we analyzed the sensitivity of the common chuckwalla, Sauromalus ater, a vegetarian lizard restricted to western North America's warm deserts, to predicted increases in temperature and aridity. We also assessed the response by their primary food plants to these changing conditions. Our study area included both east-west and elevational aridity gradients. At the eastern, most arid end of this gradient the highest population densities of chuckwallas were restricted to the top elevation category, 600-699 m. In the middle of the east-west gradient, higher chuckwalla densities occurred at elevation categories of 400-599 m and above. At the western, least arid end of the gradient, high chuckwalla densities occurred from elevation categories beginning at 200 m. Their food plants mirrored that distribution trend. We also constructed independent habitat models to predict current and future suitable ranges for both the lizards and their food plants. Potential climate refugia exist where modeled current and predicted future ranges overlap. Our empirical elevation data for where chuckwallas and their food plants exist at higher densities mirrored the climate refugia predicted by our models; current higher density populations largely already reside in putative climate refugia. Chuckwallas residing below these refugia will find conditions increasingly challenging, and all populations will need to shift to higher elevations if future levels of aridity exceed the values used in our models.