IRA FLATOW, host:

This is Talk of the Nation: Science Friday, I'm Ira Flatow. Later in the hour we'll be talking about science policy and bioethics, but first when the climate changes due to global warming, plants and animals either find a new place to live, or adapt over time, or just die out.

So, what does that mean for tropical areas which are very sensitive to temperature change, and already the plants and animals on there are living in a very warm spot. Writing this week in the journal Science are a group of researchers looking for answers in the tropics of Costa Rica, and they studied how ants, and moths, and shrubs, and other tropical plants might deal with increasing temperature.

And in their study they say that the legendary biodiversity of the tropics may be threatened by even small increases in temperature. Joining me now to talk about it is one of those researchers, Robert Colwell. He's a professor in the department of ecology and evolutionary biology at the University of Connecticut in Storrs. He joins us by phone from California. Welcome to the program, Dr. Colwell.

Dr. ROBERT COLWELL (Researcher, Department of Ecology and Evolutionary Biology, University of Connecticut): Thank you, Ira, it's a pleasure to be here.

FLATOW: Thank you. Why did you - first tell us where in Costa Rica did you study?

Dr. COLWELL: We worked at - out of the La Selva Biological Station, which is in the Atlantic lowlands, basically at sea level - a little bit above sea level, which is a large, protected area of old-growth forest, but it's connected to a continuous corridor of forest that's Braulio Carrillo National Park that rises from sea level to the top of a volcano, Volcan Barva, at 3,000 meters, about 10,000 feet above sea level.

So, we worked first at La Selva for actually for 10 years on some of these groups, and then for five years worked up the mountain on a rough, rugged trail with shelters built along the way to collect data on the distribution of the organisms you just mentioned, along this elevational transect.

FLATOW: And it's important to have that elevational transect as you study what happens over time?

Dr. COLWELL: Absolutely. In fact they're very rare things, this transect is the last remaining continuously forest transect between somewhere in Mexico and somewhere in South America, and it's only there because the organization had a public campaign in the 1980s to protect it, and now it's part a national park system.

FLATOW: Now, we've seen in other places around the world that as it gets warmer at sea level, we know it gets cooler as you go up the mountains, would we not expect the plants and animals to follow that coolness up the mountain down there?

Dr. COLWELL: We do expect them to do that if they can. The other side of the same volcano, if you saw a photograph of that, shows what is more typical at tropical mountains. There's a severe habitat fragmentation, usually for very successful farming activities in Costa Rica, for dairy farms and so on.

So, think of an orchid living in an old-growth tree that somehow has to find its way to a 600 meters higher place in the next century. Without losing track of things, and if there's a gap in the habitat it's very difficult.

FLATOW: It can't cross the farmland to get...

Dr. COLWELL: Right across the farmland.

FLATOW: Yeah. But - so, did you find this to be case that these species are threatened? These plants and animals are threatened?

Dr. COLWELL: Well, we don't have any base line data for this transect. In fact there are only two public studies of actual documented elevational movements in the tropics both from another place in Costa Rica Monte Verde, where by good fortune there were some data from the 1980s that could be compared.

So, our data will be very valuable in 10, 20 years, but as of now, we simply have to conjecture based on the distributions of the species.

FLATOW: And what's your conjecture

Dr. COLWELL: Well, we found that over half of these species, at least for the transect we looked at, the range over which these - each of the species occurs is so narrow that if the climate zones move up 600 meters, the new range of those species, the projected range will no longer overlap any part of the current range. So, there's a gap between where they're growing now, and where they will have to later on if this happens.

FLATOW: And what kinds of plants are we talking about? What kinds of animals are we talking about?

Dr. COLWELL: Well, Catherine Cardelus of Colgate University is one of our co-authors, and she collected data on 550 species of epiphytes that would be ferns, orchids, bromeliads, perching plants, things that live in the limbs of trees.

And then Alex Gilman of the UCLA collected data on ground living shrubs and herbs in the coffee family, and these are all native plants, but in that family 80 some of those, 84 of those species up and down the gradient, So, those are the plants that we looked at.

FLATOW: And are there plants that might not be able to move up?

Dr. COLWELL: Well, I'm thinking particularly of these epiphytes that need trees to live in, and if there are no trees to live in, that makes it a little hard.

FLATOW: Yeah. Just...

Dr. COLWELL: But the moth groups that (unintelligible) our co-author from Germany looked at, these moss are all - their larvae, their caterpillars feed on particular species of plants. So, they depend upon plants moving up, if they are going to be able to move up to the mountains. So, that's another complication.

FLATOW: So, outside it's a whole web - a whole chain that has to move up together?

Dr. COLWELL: That's right, and it's not likely to in fact - each species is likely to move in an idiosyncratic way, some a little more, some a little less. And some of them are wide ranging, some are more narrow ranging.

So, there will probably be a shuffling of communities, that actually has been normal in the kinds of up and down movements over the glaciation cycles on the earth. We know that the current communities are different than they were during other periods like this.

FLATOW: So, what happens to the plants that already are at the top?

Dr. COLWELL: Well, once they are the top have nowhere to go, unless there's some other population of those same species on another higher mountain. They will be forced to a lower and lower fitness and may go extinct.

FLATOW: Wow.

Dr. COLWELL: This is the same problem we have in temperate mountains, of course. There's another article in the same issues of Science on a wonderful study on Yosemite National Park, based on data taken a 100 years ago by Joseph Grinnell of the Museum of Vertebrate Zoology at Berkley, and they were able to go back to the very same places, and find that overall there has been a shift upwards, but very - quite varied among different species in how they're reacting.

FLATOW: Are there people living up at these levels too with the - as you move up the side of that volcano?

Dr. COLWELL: Oh, yes. In fact the (unintelligible) Korean National Park is basically a peninsula of forest surround by farmland and forest fragments on each side of it. And the - when it was purchased, some of it was farms, and has regrown, although there was a core of old-growth habitat.

FLATOW: Might you get non-native plants and pests that move up where they were not, and move into places and niches they would not before?

Dr. COLWELL: Well, that's possible. I think that's more likely in the lowlands and that's another concern that we have. The lowlands, of course, is the warmest forest on Earth now, they always are the warmest forest on the Earth, the equatorial lowland rain forest.

So, when it gets warmer there, unless those plants have somehow have an ability to tolerate additional warming, which many believe they do, but we're not so sure, unless they have that, those lowland plants will move up if they can, leaving behind perhaps a decreased biodiversity in the lowlands and possibly key species that are important for ecosystem function may be affected as well.

FLATOW: Is this a typical tropical area? In other words if you're studying in this place, in this volcano in Costa Rica, can you apply it to other places in the tropics?

Dr. COLWELL: Absolutely. I should say to wet forests.

FLATOW: Mm-hm.

Dr. COLWELL: I mean, there are - different things happen in dry forests. So, let's stick to wet tropical forests. Everywhere on earth, it's been looked at. These elevational distributions of these species have very narrow bands of occurrence on these mountains, compared to temperate mountains, where things are much broader.

FLATOW: Mm-hm. And is there anything besides in general, you know, halting global warming around the world? Is there anything locally that can be done to mitigate any of this?

Dr. COLWELL: Well, the most important thing that can be done is to protect and restore elevation gradients of continuous habitat, to provide a corridor for these movements to happen.

FLATOW: In that - you're saying to bring back the natural forest to where the farm land is?

Dr. COLWELL: That's right. And there's - actually there's some of that was done with this very park. When it was first established, there were some edges - some areas on the edge that were farmland, and have now gone into late second growth.

Secondary forests in the tropics grow very fast, and if they're near sources of seeds and the right kinds of animals to disperse those seeds, they can often regrow very quickly into habitat that's usable. Even by old-growth-forest species can go through these forests.

FLATOW: Mm-hm.

Dr. COLWELL: It's the open areas that are a problem for movements for a lot of birds and mammals…

FLATOW: Mm-hm.

Dr. COLWELL: And of course, for insects, they're dependent on the plants.

FLATOW: Mm-hm. So, I guess if you're an environmentalist, and you're trying to plan a nature preserve or some place you'd like to then keep it to a way the forest will stay. So you…

Dr. COLWELL: Exactly. And we - for a long time we've been saying, well, we need corridors between Nicaragua and Costa Rica, for example, in the lowlands, which we do need, that's important. But escape by going to higher latitudes is not going to happen for tropical species, because between the Tropic of Cancer and the Tropic of Capricorn, it's basically constant average temperature.

From the tropics north of the pole, it goes down, as you know…

FLATOW: Mm-hm.

Dr. COLWELL: To lower and lower temperatures in a pretty straight-line way. But between say, Acapulco and Rio, any beach you go to is going to be the same temperature.

FLATOW: Mm-hm. So what would you like to study next? What do you need to know next?

Dr. COLWELL: Well, I would love to see - this is probably not something I'd do myself - but I'd love to see experimental research done, which is - very little has been done bringing plants and other organisms from different points along a single gradient, and growing them at a - in the lowlands, and mid-elevations, and high-elevations, and see how they respond to those temperatures.

This was done a century ago almost, well, 80 years ago in California, some very famous studies. But basically, this has been done - nothing's been published like that for tropical organisms. Then for animals that are not of ethical concerns, for example, like insects, you could do laboratory experiments to see what their tolerances are.

FLATOW: Mm.

Dr. COLWELL: People that have done that, find that a lot of tropical insects are now living near their upper-thermal tolerance right now, which means they're the ones that might be in trouble.

FLATOW: Yeah, right there - it's as hot as it can get for them right now.

Dr. COLWELL: Right. And right now, the temperature in the tropics is believed to be within one degree of the hottest it's been in the last two million years. So, if these lowland organisms are retaining their ancestral tolerances from, say, 10-15 million years ago, they somehow managed to go through all of those glaciations and keep them.

So, I mean, I'm hoping that there are hidden adaptations, and these lowland plants will allow them to withstand these changes.

FLATOW: Good luck to you, Dr. Colwell, in your search.

Dr. COLWELL: Thank you very much, Ira. It's been a pleasure talking to you.

FLATOW: You're welcome. Dr. Robert Colwell is a professor in the department of ecology and evolutionary biology professor at the University of Connecticut in Storrs, Connecticut. The main campus of the University of Connecticut. We're going to take a short break.

When we come back, we're going to switch gears, and talk about science, and a kind of public policy. And before that, we're going to also talk about (unintelligible) bacteria. It's one species. Very interesting. So 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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