Lizard populations around the world are in danger of going extinct. Dr. Barry Sinervo of UC-Santa Cruz explains that warming temperatures are to blame, limiting the amount of time the lizards have for gathering food and for reproduction. Changing Planet is produced in partnership with the National Science Foundation.
ANNE THOMPSON, reporting:
Whether they're crawling, climbing, or even leaping, lizards are one of the most common reptiles on Earth. Over four thousand different species can be found living on every continent except Antarctica.
But now after decades of surveying lizard populations around the world, scientists have found that rising temperatures due to climate change are driving many lizards to extinction. If current rates continue, not only could lizard populations around the world be in serious trouble, but entire food chains could be in jeopardy.
Dr. BARRY SINERVO (UC-Santa-Cruz): By the year 2080, we would actually not just be losing populations at that point, we would have actually lost about one-fifth of the world's diversity of lizards.
THOMPSON: Dr. Barry Sinervo is an evolutionary biologist at UC-Santa Cruz whose research is partly funded by the National Science Foundation. He says that lizards, like many reptiles, are especially susceptible to changes in temperature because they're cold-blooded and unable to regulate body temperature. At night when it's cooler, their body temperatures drop significantly. So to warm up the next morning, they must bask in the sun.
SINERVO: See the sun? A lizard would actually crawl out and find a really nice warm snuggly spot.
THOMPSON: And when lizards get too warm, they must retreat to the shade to cool down, and find their perfect body temperature.
SINERVO: There is a period during the day where it's way too high for the lizards to be active.
THOMPSON: Sinervo says the rising temperatures means the lizards have to spend more time in the shade, giving them less time to do such things as forage for food and find a mate for reproduction.
SINERVO: If you're a female and you have to stay in for, like, three or four hours a day that actually pushes you to the brink of extinction. And they don't die but they don't reproduce that year. And that causes the population to decline in numbers. If that happens another year in a row, the population declines again. Two or three years of that and you might actually see the lizards go extinct in that population.
THOMPSON: Lizard populations are dying at such a fast rate, Sinervo says, that one of his biggest fears is that the lizards will not have enough time to adapt to rapid changes in climate. In Mexico, he has seen a devastation of lizard populations in the recent years.
SINERVO: We have literally seen the lizards in Mexico shut down reproduction because it's been hot.
THOMPSON: Sinervo and his team monitor lizard populations in several locations, including Mexico and here, near Los Banos, California, home to one of the most common lizards in western North America, the side-blotched lizard.
SINERVO: Can you see that, conspicuous blotch on their sides? And this one's one that we've known of. Probably he’s-- his mark is-- oh he is this year’s, so he is one-year-old.
THOMPSON: In addition to monitoring lizards, he sets up a system of data recorders, that act as specialized thermometers, which mimics how lizards absorb heat from the sun.
SINERVO: This is the lizard models. These are simulating the size and shape and color of a lizard, so we know what their thermal characteristics are.
You go to where the lizards love to be. So it's like finding-- you go out that distance and then I'd really got to be there because that's where I see the lizards. So we're trying to simulate the brain of a lizard with respect to temperature.
THOMPSON: Sinervo and his students have set up data loggers like these at several locations around the world, in places where lizards are in peril. Here in the mountain pine forests outside of Santa Cruz, he hopes to find the alligator lizard.
SINERVO: Let's check down this slope. They like kind of these, in hotter areas, these north-facing slopes where they're open.
THOMPSON: He's unable to locate any alligator lizards on this day, but he does find clear signs of climate change in the surrounding hills.
SINERVO: One thing that we found that's really quite striking is that wherever we find lizard extinctions, the pine trees are dying at a very high rate. And so we have a bunch of pine deaths just behind us here up on this slope.
THOMPSON: Sinvero's concerns are not just for lizards themselves, but how the loss of lizards could impact entire ecosystems, up and down the food chain.
SINERVO: We know that if the lizards disappear from a site, then the predators that feed on them, the snakes and the birds, will also disappear. They catch and control insect populations. And so we are seeing a break in a vital link in our ecosystems. This is true in California desert, mountain ecosystems. We go to Europe, we see exactly the same problem there. We got to South America; we see exactly the same problem. So it's like a global problem that seems to be cropping up in our data as we survey for the lizards.
THOMPSON: And as temperatures continue to rise, Sinervo believes lizards may be one of the so-called canaries in the coal mine for the impacts of climate change on the ecosystem.
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What were the researchers trying to find out? (Was there a hypothesis?)
Does this news report indicate:
- the independent variable?
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While there's been extensive research attempting to predict the future of Earth's vulnerable plants and animals, there have been comparatively few studies investigating the extinctions that have occurred in the past.
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