Rafael A. Lara-Reséndiz

Erosion of lizard diversity by climate change and altered thermal niches

Demise of the Lizards Despite pessimistic forecasts from recent studies examining the effects of global climate change on species, and observed extinctions in local geographic areas, there is little evidence so far of global-scale extinctions. Sinervo et al. (p. 894; see the Perspective by Huey et al.) find that extinctions resulting from climate change are currently reducing global lizard diversity. Climate records during the past century were synthesized with detailed surveys of Mexican species at 200 sites over the past 30 years. Temperature change has been so rapid in this region that rates of adaptation have not kept pace with climate change. The models were then extended to all families of lizards at >1000 sites across the globe, and suggest that climate change-induced extinctions are currently affecting worldwide lizard assemblages. A historical record of lizard populations in Mexico is used to parameterize models that predict global effects of climate change. It is predicted that climate change will cause species extinctions and distributional shifts in coming decades, but data to validate these predictions are relatively scarce. Here, we compare recent and historical surveys for 48 Mexican lizard species at 200 sites. Since 1975, 12% of local populations have gone extinct. We verified physiological models of extinction risk with observed local extinctions and extended projections worldwide. Since 1975, we estimate that 4% of local populations have gone extinct worldwide, but by 2080 local extinctions are projected to reach 39% worldwide, and species extinctions may reach 20%. Global extinction projections were validated with local extinctions observed from 1975 to 2009 for regional biotas on four other continents, suggesting that lizards have already crossed a threshold for extinctions caused by climate change.

Thermoregulation of two sympatric species of horned lizards in the Chihuahuan Desert and their local extinction risk.

Thermoregulatory studies of ectothermic organisms are an important tool for ecological physiology, evolutionary ecology and behavior, and recently have become central for evaluating and predicting global climate change impacts. Here, we present a novel combination of field, laboratory, and modeling approaches to examine body temperature regulation, habitat thermal quality, and hours of thermal restriction on the activity of two sympatric, aridlands horned lizards (Phrynosoma cornutum and Phrynosoma modestum) at three contrasting Chihuahuan Desert sites in Mexico. Using these physiological data, we estimate local extinction risk under predicted climate change within their current geographical distribution. We followed the Hertz et al. (1993, Am. Nat., 142, 796-818) protocol for evaluating thermoregulation and the Sinervo et al. (2010, Science, 328, 894-899) eco-physiological model of extinction under climatic warming. Thermoregulatory indices suggest that both species thermoregulate effectively despite living in habitats of low thermal quality, although high environmental temperatures restrict the activity period of both species. Based on our measurements, if air temperature rises as predicted by climate models, the extinction model projects that P. cornutum will become locally extinct at 6% of sites by 2050 and 18% by 2080 and P. modestum will become extinct at 32% of sites by 2050 and 60% by 2080. The method we apply, using widely available or readily acquired thermal data, along with the modeling, appeared to identify several unique ecological traits that seemingly exacerbate climate sensitivity of P. modestum.

Thermoregulation during the summer season in the Goode’s horned lizard Phrynosoma goodei (Iguania: Phrynosomatidae) in Sonoran Desert

Reptiles in desert environments depend on habitat thermal quality to regulate their body temperature and perform biological activities. Understanding thermoregulation with respect to habitat thermal quality is critical for accurate predictions of species responses to climate change. We evaluated thermoregulation in Goode’s horned lizard, Phrynosoma goodei, and measured habitat thermal quality at the Reserva de la Biosfera El Pinacate y Gran Desierto de Altar, Sonora, Mexico, during the hottest season of the year. We found that field-active body temperature averaged 38.1 ± 0.38°C, preferred body temperature in laboratory averaged 34.9 ± 0.18°C and preferred body temperature range was 32.5-37.3°C. Operative temperature (i.e. environmental temperature available to the lizards) averaged 43.0 ± 0.07°C, with maximum temperature being near 70°C, and 62.9% of operative temperatures were above preferred body temperature range of P. goodei. Microhabitat thermal quality occupied by the lizards was high in the morning (7:00-10:30) and afternoon (5:50-dusk). We found that despite strong thermal constraints P. goodei was highly accurate and efficient in regulating its body temperature and that it presented a bimodal thermoregulatory pattern, being active in the mornings and in the evenings in order to avoid high mid-day environmental temperatures. Despite its thermoregulatory ability, P. goodei may be vulnerable to climate warming.

Termorregulación diurna y nocturna de la lagartija Phyllodactylus bordai (Gekkota: Phyllodactylidae) en una región semiárida del centro de México

Los reptiles nocturnos dependen de la calidad termica del habitat para regular eficientemente su temperatura corporal y realizar sus actividades biologicas diurnas y nocturnas. Previamente, se ha sugerido que los ectotermos nocturnos mantienen estrategias diferentes para termorregular entre el dia y la noche. Por lo tanto, los objetivos en este estudio fueron: (1) examinar las temperaturas corporales en campo y preferidas en laboratorio de la lagartija nocturna Phyllodactylus bordai durante la fotofase y escotofase y cuantificar la temperatura operativa disponible; y (2) evaluar la precision, eficiencia en la termorregulacion y la calidad termica del habitat en ambas fases. El area de estudio se centro en una region semiarida del centro de Mexico. Los resultados mostraron que P bordai presento un patron bimodal de termorregulacion con temperaturas corporales altas durante la fotofase y bajas en la escotofase; ademas mantuvo una estrategia euriterma caracterizada por un amplio intervalo de temperaturas corporales; y finalmente, fue una especie altamente precisa y eficiente en la termorregulacion durante ambas fases. La region semiarida del centro de Mexico proporciono a P. bordai microclimas termicamente optimos y estables dentro de cada fase para alcanzar y mantener su temperatura en el intervalo optimo con relativamente poco esfuerzo termorregulatorio. En general, los resultados estuvieron de acuerdo con estudios y predicciones anteriores y expanden el trabajo previo en ecologia termica de reptiles nocturnos.