National Park Service Despite many claims about climate change wreaking havoc on biodiversity, there are very few experimentally-validated models that can accurately explain recent extinctions and project future extinctions based on rising temperatures. However, a study in last week's Science conclusively links extinctions of Sceloporus lizard species to climate change and forecasts a gloomy future for many other lizard species around the world.

In general, most lizards should be relatively resilient to rising temperatures, since they can regulate their own body temperature by basking in the sun or retreating to shady refuges to cool down. However, if temperatures rise so much that lizards cannot spend enough time out foraging to meet their energetic needs, extinction at a local level is possible. These time restrictions would be especially detrimental in the reproductive season, when energetic demands are particularly high. The study first tests whether this scenario might be responsible for past extinctions of lizard species in the genus Sceloporus.

The authors constructed lizard replicas to measure and record the operative temperatures that the animals would endure under a particular set of environmental conditions. These models were deployed at 4 sites in Mexico during the breeding season—two sites with current Sceloporus populations and two sites where Sceloporus had gone locally extinct.

The models showed that lizards' operative temperatures at the sites where they'd gone extinct would be so high that that they would be forced to retreat to shady places for more than 3.85 hours per day. At the sites where lizard populations still persist, the lizards were not subject to the same time restrictions, and could spend more time out in the environment foraging.

From this comparison, the authors inferred that lizard populations in areas where the time restrictions exceeded 3.85 hours per day during the reproductive period were likely to go extinct in that location. To validate this prediction, they used air temperature records from 200 sites in Mexico where Sceloporus populations either existed or had previously existed; twelve percent of these populations had gone locally extinct since 1975.

In accordance with the results of the lizard replica test, the air temperatures at the now-extinct sites suggest that these populations would have had time restrictions greater than 3.85 hours per day, while the time restrictions at sites that still have lizard populations were below that cutoff.

With their time restriction assumption validated, the authors then made projections for future extinctions in Mexico and around the world. If temperatures in Mexico continue to rise at the current rate, the authors predict that 58 percent of Sceloporus populations in Mexico will go extinct by 2080. To calculate global extinction risk, the authors obtained daily maximum temperatures in the home ranges of 34 different lizard families, as provided by the WorldClim database. When applied to 1214 lizard populations on four continents, the model suggests that by 2080, 39 percent of lizard populations and 20 percent of lizard species around the world will be extinct.

Lizards are limited in their ability to evolve in response to rapid climate changes, due to genetic constraints on thermal preference and relatively long generation times. Since rapid evolution to keep pace with rising temperatures may not be possible, lizard species will be forced to alter their ranges to escape the heat, but may then suffer intense interspecific competition in these preferred habitats.

While the Sceloporus model predicts a particularly dismal future for lizards, its accuracy in explaining past extinctions and its power in predicting future extinctions gives scientists some hope. With this sort of approach, we may be able to better understand the physiological and genetic factors that drive local and global extinctions in many species around the world.