Scientists studying spiny lizards in the New Mexico desert have found that current models used to predict animal extinction due to global warming may be way off. And not in a “phew, it’s better than we thought” sense.
Some current models predict that 40 percent of all lizards will become extinct by 2080 because Earth is heating faster than they can adapt. A new study published in the Proceedings of the National Academy of Sciences suggests that these models need to include more data to be considered accurate – specifically how shade is distributed in an animal’s habitat.
Lizards are affected by global warming more than many other species as they are cold-blooded, meaning they regulate their body temperature using their external environment, and even a small change in temperature can dramatically affect their wellbeing. According to Mike Sears, an associate professor of biology at Clemson University and the lead author of the study, lizards are well-suited for climate change studies as "they're like little thermostats running around."
Lizards regulate their body heat by alternating between sunny patches and shade to warm up and cool down. This is the first time scientists have looked at not just the proportion of warm to cold areas in a habitat but how they are distributed in the space, finding that spiny lizards prefer lots of little patches of shade that are easier to reach than one large area.
"Most models assume that an animal can be anywhere in its environment at any time, which doesn't account for how much energy an animal spends to regulate its temperature," said Mike Angilletta, a professor at Arizona State University and co-author of the study, in a statement. “Animals have to move and search for shade, which makes cooling down more difficult when patches of shade are far apart."
Sears first questioned the previous models when he realized they assumed a lizard can find shade whenever it pleases, anywhere in its environment. Having studied lizards for 20 years, he knew it was more complicated than that, with lizards expending time and energy searching for shade, factors that were not included in these models.
"Depending on the complexity of the environment, previous estimates of extinction may be too high or they might not be high enough," Sears explained.
The team used both computer simulations and studied the animals up close in New Mexico to determine how the shade available to these populations impacted their ability to maintain their body temperature in the safe range. They discovered that the lizards found it easier to regulate their temperature and cool down when there was a larger number of small patches of shade rather than one large one.
These results show that the lizards are a lot more dependent on the vegetation and rocks of their environment than previously thought. Unfortunately, global warming could mean fewer plants and a changing landscape that offers less shade, which could significantly reduce their chances of survival.
This study highlights that missing data in other current models of predicted species extinction might be off target as well, having repercussions for many animals, not just the spiny lizard.
"If we really want to understand how populations of organisms will respond to climate change, we can't use a simple, back-of-the-envelope method," Sears said. "We need to think on a finer scale than we have been."
Researchers arranged shade in different sized clusters to test lizards' thermoregulation. Michael Angilletta, Arizona State University, and Michael Sears, Clemson University