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.