A study of a lizard species in Arizona revealed that nearly 70 years’ worth of climate-related extinction occurred in just seven years.
Researchers surveyed populations of the Yarrow’s spiny lizard in 18 mountain ranges in southeastern Arizona and analyzed the rate of climate-related extinction over time. “The magnitude of extinction we found over the past seven years was similar to that seen in other studies that spanned almost 70 years,” says John J. Wiens, a professor in the ecology and evolutionary biology department at the University of Arizona and senior author of the study in Ecology Letters.
The Yarrow’s spiny lizard native to the southwestern US and western Mexico can be spotted in oak and pine forests in 18 of Arizona’s Sky Islands mountain ranges. Wiens and his group did initial surveys of the Yarrow’s spiny lizard in these mountain ranges in 2014 and 2015.
In 2021 and 2022, Wiens, along with Kim Holzmann, his former master’s student and the new study’s lead author, and Ramona Walls, a part-time researcher at the University of Arizona’s BIO5 institute, resurveyed to investigate if there had been any changes in the lizard populations since then.
They found that about half of the lizard populations at lower elevations had disappeared. This is because temperatures are warmer at lower elevations, Wiens says, and the lizards at lower elevations were presumably not able to tolerate the increasing heat. This loss of low-elevation populations is a signature pattern of climate change, he says. “The rate of extinction in such a short time period was shocking,” Wiens says.
After comparing the findings to historical records from the same mountain ranges, Wiens’ group found that the average extinction rate of the lizard populations at low elevations had tripled over the past seven years, relative to the preceding 42 years. Although previous studies have predicted that climate-related extinctions will increase with the rising pace of global warming, Wiens says he hasn’t seen any showing that this acceleration of extinction has already happened.
Also, a distinct 3-million-year-old lineage of the Yarrow’s spiny lizard from the Mule Mountains, near Bisbee, may be completely extinct by 2025, Wiens says. “The low-elevation populations in the Mules were fine in 2014. Now the only ones that we have found left were within about 300 feet of the top of the mountain in 2022, and they appear to have been losing about 170 feet per year,” he says.
However, not all low-elevation populations went extinct between the surveys, Wiens says. For example, two populations that occurred at very low elevations survived. Before they disappeared, the research group had collected genomic data from most of those populations in 2014 and 2015. They found that those populations that were less genetically variable and were exposed to greater climate change effects were the ones that tended to go extinct. This suggests that the populations with less genetic variation had less ability to adapt to climate change.
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