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No climate safety for lizards

March 14, 2014
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By Diane Luckow

Scientists have long believed that lizards and other cold-blooded animals are “climate proof,” because their heat tolerance seemed sufficient to cope with the midday heat in the world’s hottest places.

But a new study from SFU researchers shows that lizards and amphibians have little capacity to cope with climate change.

After studying scientific data from more than 300 cold-blooded species, graduate student Jennifer Sunday and biology professor Nick Dulvy discovered these species can only tolerate temperatures up to 50 degrees Celsius, regardless of where they live on Earth.

“Up to now we thought that gave lizards 15 to 20 degrees of thermal safety—more than enough to cope with climate change,” says Dulvy.

But he and Sunday also found that previous studies examining these animals’ heat tolerance relied on air-temperature data from weather stations that are typically housed in shaded boxes four feet off the ground.

“That’s not how a lizard experiences the world,” says Dulvy. “It’s one or two inches off the ground and sitting out in full sunshine.”

So they tried modeling the air temperatures these animals would actually experience sitting in full sunshine, full shade or in a burrow in habitats ranging from tropical lowlands and highlands to colder climes much further north and south.

Not surprisingly, the radiated heat and cold from the ground results in much higher, and lower, habitat temperatures than previously recorded.

“When we compared heat tolerances, we discovered they’re right at the limit,” says Dulvy. “Eight out of the 10 lizards we looked at don’t have enough heat tolerance to cope with what they’re experiencing right now. The only way they get by at the moment is by using shade.”

The researchers also looked at frogs, discovering that their wet skin, which cools them through evaporation, is continuing to keep them safe from the hottest temperatures.

“Frogs can survive climate change, but only if they’re wet,” says Dulvy.

He says the study’s findings reinforce the need to preserve rainforests and wetlands to help cold-blooded species cope with climate change over the coming years.

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