Why do lizards die

Knowledge : Reptiles die from heat. Every fifth species of lizard will be exterminated by 2080

If climate change continues to increase temperatures, one in five species of lizard could be extinct by 2080, fear Barry Sinervo of the University of California at Santa Cruz and his colleagues around the world (Science, volume 328, page 894). Because the nimble reptiles withdraw into the shade from certain heat levels and wait motionless for cooling. If the temperature rises, the compulsory breaks become more frequent and longer, during which the lizards do not hunt either. Climate change is worsening the food situation, especially for the lizards, which already live in warmer regions near their physiological heat limit.

Sinervo discovered this connection when he was investigating the fate of 48 species of lizards in Mexico. Since 1975, twelve percent of these species had disappeared. The ecologist was particularly puzzled that in no case had the habitat of the extinct lizards disappeared. Most of the species lived in national parks or other protected areas.

In an experiment, the researchers unmasked climate change as the culprit: They built devices that heat up similarly to a lizard when sunbathing. For four months at a time, the devices stood in areas in which the lizards had either already disappeared or were still darting cheerfully across the earth - and recorded the temperature. The result of the experiment was clear: In all regions where the lizards had disappeared, there was a dramatic decrease in the times with temperatures in which the respective species of lizard hunted.

With their data, the researchers developed a model that uses the highest air temperature, the body temperature at which the respective lizard species is still active, and the hours in which the heat gives the animals a forced break to calculate the risk of extinction for the species examined. For precisely those areas from which the lizards had already disappeared, the model predicted an extinction based on the temperature data.

Next, Barry Sinervo and his colleagues collated all of the available data for the 300 or so species of lizard around the world and entered them into their model along with the likely future maximum temperatures. Worldwide, six percent of all lizard species are likely to become extinct by 2050. By the year 2080, this number will soar to 20 percent.

The wave of extinction by 2050 can hardly be stopped if all known measures to slow down climate change are implemented immediately, because the climate reacts very slowly. Some species that are only expected to become extinct in the following years by 2080 could, however, save their lives quickly. Roland Knauer

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