Whither the lizards?

That’s what biologist Barry Sinervo has been asking lately. In a study published on Friday in Science, Sinvero’s team raised the alarm about lizards around the world, saying that at the very least 6 percent of lizard species will go extinct by 2050, and as many as 20 percent could disappear forever by 2080.

Sinervo and his colleagues make this claim based in part on surveys they did in Mexico.

Sinervo and his team surveyed 48 species of spiny lizards at 200 sites on the Yucatan peninsula in Mexico that had been studied in detail from 1975 to 1995 and found that 12 percent of that population had already become extinct by 2009.

The lizards lived in well-protected areas like national parks, so it wasn’t habitat destruction that caused the population decline, Sinervo said. Instead, it was a tale of rising temperatures disrupting lizard lives [San Francisco Chronicle].

A lot of studies point the finger at global warming in one way or another, but Sinervo’s team says that there’s a good reason why lizard populations would fade in a warmer world.

Global warming appears to be lengthening the period of the day when lizards must seek shelter or risk fatal overheating. In the breeding season, that sheltering period is now so long that females of many species are unable to eat enough food to produce eggs and offspring [Washington Post].

To bolster their claim, the team created their own fake lizards equipped with thermometers and set them out in the Mexican sun. In two areas where the lizards seem to have disappeared, Sinervo says, there were more than 9 hours a day on average that would’ve been too hot for the lizards to come out of hiding. In two areas where lizards still remained, the midday heat was far less brutal.

In an accompanying essay in Science, Raymond Huey writes that the case is a strong one, and worrisome. However, he wonders, can you really make extinction predictions based on these findings?

Huey warns that not seeing lizards doesn’t mean that they’re not there. They may just have been overlooked. “Populations go up and down,” he says. Still, he notes, Sceloporus [a Mexican lizard] is very conspicuous. “It would be hard to miss” [Nature].

Only follow-up surveys can truly confirm that the lizards’ slow disappearance is real and not “psuedo-extinction,” Huey says. Sinervo and his team are presently in Spain, preparing to do a survey in the Pyrenees Mountains.

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Image: Fausto Mendez de la Cruz