Thermal ecology of the federally endangered blunt-nosed leopard lizard (Gambelia sila)

Abstract

Recognizing how climate change will impact populations can aid in making decisions about approaches for conservation of endangered species. The blunt-nosed leopard lizard (Gambelia sila) is a federally endangered species that, despite protection, remains in extremely arid, hot areas and may be at risk of extirpation due to climate change. We collected data on the field-active body temperatures, preferred body temperatures and upper thermal tolerance of G. sila. We then described available thermal habitat using biophysical models, which allowed us to (i) describe patterns in lizard body temperatures, microhabitat temperatures and lizard microhabitat use; (ii) quantify the lizards’ thermoregulatory accuracy; (iii) calculate the number of hours they are currently thermally restricted in microhabitat use; (iv) project how the number of restricted hours will change in the future as ambient temperatures rise; and (v) assess the importance of giant kangaroo rat burrows and shade-providing shrubs in the current and projected future thermal ecology of G. sila. Lizards maintained fairly consistent daytime body temperatures over the course of the active season, and use of burrows and shrubs increased as the season progressed and ambient temperatures rose. During the hottest part of the year, lizards shuttled among kangaroo rat burrows, shrubs, and open habitat to maintain body temperatures below their upper thermal tolerance, but, occasionally, higher than their preferred body temperature range. Lizards are restricted from staying in the open habitat for 75% of daylight hours and are forced to seek refuge under shrubs or burrows to avoid surpassing their upper thermal threshold. After applying climatic projections of 1 and 2°C increases to 2018 ambient temperatures, G. sila will lose additional hours of activity time that could compound stressors faced by this population, potentially leading to extirpation.

Thermoregulation and thermal performance of crested geckos (Correlophus ciliatus) suggest an extended optimality hypothesis for the evolution of thermoregulatory set‐points

“…However, our results suggest that crested geckos have a fairly typical thermal biology for a lizard. When provided a thermal gradient, they actively thermoregulate to within a 3–4°C set‐point range and their running performance is affected by temperature similar to other species (Huey, 1982; Ivey et al, 2020; Muñoz et al, 2016; Tomlinson, 2019). Although the preferred and optimal temperatures of crested geckos are below those of many diurnal, heliothermic species, they are very similar to estimates for other nocturnal and shade‐dwelling species (Brown, 1996; Muñoz et al, 2016; Telemeco et al, 2017).…”

“…In small‐ to medium‐sized lizards, groin temperature is a reliable proxy for cloacal temperature and has reduced risk of discomfort or injury (Camacho et al, 2018). For each individual, we used data from their final 2.5 hr in the gradients to estimate the preferred body temperature (PBT) as the mean temperature experienced, the thermal set‐point range ( T SET ) as the 25–75% interquartile range (Hertz, Huey, & Stevenson, 1993; Ivey et al, 2020), and the voluntary thermal minimum and maximum as the lowest and highest body temperatures experienced, respectively (Camacho et al, 2018).…”

The thermal ecology and physiology of reptiles and amphibians: A user's guide

“…The length of time varies widely, but researchers should attempt to allow animals to thermoregulate for as long as possible to ensure they are behaving somewhat normally and that the data encompass potential circadian rhythms in thermoregulation. Typically, using the interquartile range of selected T b for one 24‐hr period is ideal for establishing T set , although sometimes significantly shorter or more specific time periods are appropriate, for example when attempting to reduce diel variation and characterize T set only during active hours (Camacho & Rusch, 2017) or when studying endangered animals that scientists are only permitted to handle for limited periods of time (e.g., Ivey et al, 2020).…”

Micro-Climatic Amelioration in a California Desert: Artificial Shelter Versus Shrub Canopy

“…California is home to a diversity of dryland landscapes, dominated by many species of shrubs (Stuart and Sawyer 2001). Ephedra Californica (Mormon Tea) is a common foundation shrub species that benefits other plants (Lortie et al 2018) and animals (Ivey et al 2020).…”

“…Shrubs and structural heterogeneity are important components of ecosystems relevant to the conservation and restoration of other plants and animals. A shelter, vegetation, or artificial of any sort in deserts provides amelioration or even just differences in the temperature and light at fine-scales that provides plants and particularly animals with thermal options(Ivey et al 2020;Attum and Eason 2006). The hypothesis that…”