Study Ties Warming to Decline in Frog Populations A new study links climate change to frog extinction in the Central and South American tropics. What might the connection mean for global biodiversity?
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Study Ties Warming to Decline in Frog Populations

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Study Ties Warming to Decline in Frog Populations

Study Ties Warming to Decline in Frog Populations

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  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
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A little bit later we'll be joined by environmentalist Lester Brown. But first, a new study out this week links global climate change to the extinction of frogs in the South and Central American tropics. The area used to be home to at least 110 species of brightly colored Harlequin frogs. Now, of those 110 species, oh, about 70 percent--that's 7-0, 70 percent--have disappeared. Scientists say their decline closely matches the rise in temperature caused by climate change. But it's not the hot weather that is killing the frogs; at least, not directly. A skin fungus is likely the culprit.

This study explains how climate change is good for the fungus, bad for the frogs. Dr. Andrew Blaustein is professor of zoology and director of the Environmental Science Graduate Program at Oregon State University. He joins us by phone from his office in Corvallis.

Welcome back to SCIENCE FRIDAY, Dr. Blaustein.

Dr. ANDREW BLAUSTEIN (Oregon State University): Hi. My pleasure to be here.

FLATOW: You're welcome. Can you link--walk through us how the study links climate change to the fungus and the frog extinction?

Dr. BLAUSTEIN: OK. Essentially, what we have is we have lots of species of frogs in the tropics, and over the last several decades there's been a global decline in amphibians and there has been this indication that there were some pathogens, diseases, involved, and one of the diseases is this fungus you're talking about. It's called the batrachochytrium, or chytrid for short. And it only has certain types of temperature regimes where it can grow. It looks like global climate change has done something to make it optimum for that fungus to grow on the frogs by actually cooling down the temperatures during the day and keeping the temperatures warm at night, with increased cloud cover.

FLATOW: Hmm. Perfect for fungus growth.


FLATOW: Yep. The lead author of the study, J. Alan Pounds, says, quote, "Disease is the bullet killing the frog, but climate change is pulling the trigger."

Dr. BLAUSTEIN: And that's exactly what we thought, too. And there are a couple of other studies out there where climate change or environmental changes, such as global warming or increased or decreased precipitation and even increasing ultraviolet rays actually acts to trigger other diseases in other parts of the world.

FLATOW: Yeah. You mention in your News and Views column in the journal Nature about those other--some of those other links. Let's talk about some of those other links. For example, there is one about frogs dying from ultraviolet light that you mentioned.

Dr. BLAUSTEIN: Yeah. We think that--and we've been studying this for a number of years. Ultraviolet radiation has increased due to ozone depletion. It's affecting lots of organisms, not just frogs. It affects coral reefs, it affects insects, fishes, microorganisms. And with increasing ultraviolet rays, at least in the Western United States, and with El Nino events where there's less water, we see that sunlight hitting frog eggs in less water compromises their immune system and allows them to get a different species of fungus. So this fung--there are several fungi-type organisms around here killing amphibians.

FLATOW: And there are other connections, too, you were writing about.

Dr. BLAUSTEIN: Yeah. The other connec--well, there's all kinds of connections. You mean the other systems?


Dr. BLAUSTEIN: There are things that are going on in the Rocky Mountains with insect pests.

FLATOW: Right.

Dr. BLAUSTEIN: There's pine blister rust. There are all these parasites. The parasites (technical difficulties) something with their life cycles due to global climate change, which is shortening the life cycle. And therefore, they can do their damage even faster.

FLATOW: Hm. Is this something that was unexpected?

Dr. BLAUSTEIN: Well, people have been talking about climate change for a while, and people have been looking at diseases for a while, and actually, at least 20 years ago and maybe even before that, lots of physicians and disease ecologists would hypothesize that global climate change was going to change some disease patterns. As a matter of fact, since the 1970s, at least 30 newly emerging diseases that affect people have come about, and other diseases that we thought were controlled are starting to get...


Dr. BLAUSTEIN: ...much worse.

FLATOW: You say in your little report here, `As global change is occurring at an unprecedented pace, we should expect many other host vectors from ants to zebras to be confronted with challenges...'

Dr. BLAUSTEIN: Well...

FLATOW: ...similar to those faced by the frogs.

Dr. BLAUSTEIN: Well, we're already starting to see some of these, such as the beetles that transmit pine blister rust or pine beetles in other areas; other pathogens, other parasites. And we expect it to hit other systems. People have to start looking at it.

FLATOW: Mm-hmm. `We should also,' you write, `expect the unexpected. Terms such as "enigmatic decline" and "pathogen climate paradox" will probably dominate explanations of extinctions.' Can you explain those for us?

Dr. BLAUSTEIN: Yeah. Well, what was going on with this system in the tropics, first of all, is that we did not understand how this chytrid fungus can actually play a role, because it looked like the temperature regime was not exactly proper for it to grow. Now, with Alan Pounds' hypothesis and with the data that he generated, we now have a working model where we can see the cloud cover, the temperature regimes and all that...

FLATOW: Right.

Dr. BLAUSTEIN: ...making it optimum for the growth of the parasite. And we think other systems are going to show similar situations.

FLATOW: There were studies--I remember studies just a few years ago in mountaintops where they're finding, for example, mosquitoes that never used to grow at altitudes are now growing at certain altitudes because they're--you know, it's warming up for them high enough to grow there.

Dr. BLAUSTEIN: Well, one of those mosquitoes is the mosquito that carries malaria, and it's actually increased in altitude where its range used to be a lot lower. So we've got problems there.

FLATOW: 1 (800) 989-8255 is our number. Let's see if we can take a phone call. Hi, Steve in Chapel Hill, North Carolina. Hi, Steve.

STEVE (Caller): Hi. How are you, Ira? I wanted to ask if we could talk a moment about the human population growth and the way in which per-human consumption is growing and human population numbers seem to be increasing rapidly, and the productivity of our economic system appears to be endless, and all of this is occurring on what looks to me like a small, finite planet. And it's hard...

FLATOW: Steve? Steve, I'm going to ask you to hang on, because Lester Brown is coming on later, and he's going to talk all about this, OK?

STEVE: OK. Should I call back in?

FLATOW: Yes, why don't you do that?

STEVE: All right.

FLATOW: Thank you.

STEVE: Thank you.

FLATOW: 1 (800) 989-8255 is our number. Andrew Blaustein, what about humans? We talked about these mosquitoes. Are scientists worried about parasites, other parasites, that threaten humans becoming more deadly or widespread because of climate change?

Dr. BLAUSTEIN: Very much so. As a matter of fact, I could give you a list. There are things like diphtheria and dengue fever, which is this very strange thing called breakbone fever. It's increasing in range. It used to be mainly in the tropics; it's now cropping up into Texas. We have outbreaks of malaria in, actually, the United States, including--there were outbreaks in New York and California.


Dr. BLAUSTEIN: So yes, there are some...

FLATOW: Yeah, and there are also case of where things are getting wetter and we're seeing animals that, you know, thrive in the wetness; they might be carrying--these furry creatures that might be carrying diseases with them, too. I'm thinking of Hantavirus, things like that.

Dr. BLAUSTEIN: Absolutely. Rodents...

FLATOW: Right.

Dr. BLAUSTEIN: ...carrying these viruses--that's one of the ones that's on the list for increasing, and the rodents' range is getting a little bit bigger. Lyme disease, same thing; with habitat alteration, we have increased Lyme disease, mostly prevalent in the East, but we've got it all over North America now.

FLATOW: Hm. Tell me a bit about the frogs. What kind of detective work did it take--because we've known about these frogs dying for years. How did you narrow it down? How did the scientists narrow it down that it was this fungus?

Dr. BLAUSTEIN: Well, there's a lot of scientists working on this particular fungus and people looking at how the fungus works and how it's spreading. And there are several recent papers and some papers that are coming out that are going to show you how it spreads, but Alan Pounds, I guess, put together a really nice team of ecologists, herpetologists and atmospheric scientists, and they just got together and looked at all the correlative information, and this pattern seems to fit.

But what I want to stress is it's an interdisciplinary group that has looked at this. It's not just an ecologist or just a herpetologist. You have atmospheric scientists and really good people who are experts in those fields.

FLATOW: But it does seem like there are some skeptics, some scientist skeptics around, and I'm going to quote from an article in The New York Times, where some amphibian and climate experts who read the study said it contained definitive statements that were not supported by the data. Let me give you--an example the reporter gave was, "Our study sheds light on the amphibian decline mystery by showing that large-scale warming is a key factor." Do you think that the paper overshoots the mark a bit?

Dr. BLAUSTEIN: Well, I think that statement is pretty accurate for that system. Now a different system may show something else. It may not be the same in North America or Australia. And there's always skeptics, and some of the skeptics have some points, but generally this thing was looked at by a number of really well-qualified people, and we think it's pretty good.

FLATOW: Why do you think the frogs were so hard hit?

Dr. BLAUSTEIN: Frogs are indicators of environmental stress, and usually they're the first vertebrate type of animals that go first. They have permeable skin. They live in both water and on land, so they get a double whammy with any kind of contaminant or disease. They're really sensitive in a lot of ways to these types of perturbations.

FLATOW: And so there might be many more frogs we don't even know about that could have died out.

Dr. BLAUSTEIN: Oh, I would say so. And this is a worldwide phenomenon. I want to stress that. We're losing amphibians throughout the world, and this is just one part of an overall biodiversity crisis. This biodiversity crisis is unprecedented. It's the major extinction event of our time.

FLATOW: Hm. And so you're saying it's not just in the tropical rain forests in...

Dr. BLAUSTEIN: Oh, absolutely not. We see it right here in North America, too.

FLATOW: Mm-hmm. Where do you go from here with this work? Where are the scientists going and you yourself on this area?

Dr. BLAUSTEIN: Well, what we're looking at is we're looking at different diseases. We're looking at global climate change in various ways, and we want to do some experimental studies. This was a correlational study, a study of patterns. We want to do some experiments to see whether or not we can induce the effects that they see experimentally, and we want to see if these patterns persist in certain areas such as Australia or North America.

FLATOW: Do you think it might be possible to reverse this trend, or is it already over the tipping point, as we say?

Dr. BLAUSTEIN: The way to reverse this trend is to get control on some of the environmental laws and sign the Kyoto protocol agreement, etc. We've done pretty well with ozone depletion by signing the Montreal Protocol. We've just got to get these laws out there.

FLATOW: All right. Thank you very much, Dr. Blaustein, for taking time to talk with us.

Dr. BLAUSTEIN: My pleasure.

FLATOW: Good luck to you.

Andrew Blaustein is the director of the Graduate Program in Environmental Sciences and professor of zoology at Oregon State University in Corvallis.

We're going to take a short break and come back and talk to one of the foremost thinkers on environmental issues. We'll talk about global energy use. Are we using up the Earth? China is--the giant sucking sound that we used to talk about coming from South America, now it's coming from, you know--threatens to take over all the natural resources around the world. We'll talk about it with Lester Brown. Stay with us. We'll be right back.

I'm Ira Flatow. This is TALK OF THE NATION/SCIENCE FRIDAY from NPR News.

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