Micro and macroclimatic constraints on the activity of a vulnerable tortoise: a mechanistic approach under a thermal niche view

1. Thermal constraints imposed by the environment limit the activity time of ectotherms and have been a central issue in ecophysiology. Assessing these restrictions is key to determining the vulnerability of species to changing thermal niches and developing conservation strategies. 2. We generate an explicit tortoise model of thermal constraints at both micro and macroclimate scales based on thermophysiology parameters and environmental operative temperatures during a biologically significant period. As a study model, we use a vulnerable species of gopher tortoise (Gopherus evgoodei), whose primary habitat is the tropical dry forests in northwestern Mexico. 4. Our mechanistic model is based on a monitoring of 5-years of environmental operative temperatures (Te). Here, we use the hours of activity (ha) and hours of thermal restriction (hr), calculated from the voluntary temperature range of G. evgoodei with respect to Te, to project and compare the thermal constraints across space and time. In addition, this model was projected using a pessimistic climate change scenario for 2070 (RCP 8.5). 5. The results show that the period of activity of G. evgoodei, predicted by ha and hr, is limited by the frequency and availability of Te and differs significantly throughout the year and among years. In addition, under the RCP 8.5 scenario, we predict that hr will increase considerably and exceed the critical value (3.11 hr) placing this species as highly vulnerable. 6. We discuss and compare the period of potential activity, thermoregulation strategies, and costs and benefits with other Gopherus species. Finally, we identify critical areas to develop management strategies for protecting this Mexican endemic tortoise.