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PRI's Environmental News Magazine

Ecological Intruders

Air Date: Week of June 17, 2005

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Zebra mussels, poisonous giant toads and melaleuca trees are all invasive species which cause millions of dollars of damage and the elimination of native creatures all over the globe. Some say invaders are the biggest threat to our environment this century. Host Steve Curwood talks to Alan Burdick, senior editor at Discover Magazine, who has written a book on the subject. Burdick’s central theme “what is nature?” asks us to question our assumptions of whether natural landscapes even exist anywhere but in our own desires.


CURWOOD: Evolution, the way Charles Darwin saw it, is something that takes place over millennia. But once humans started farming and moving around the planet, we started shuffling species at a far faster rate than natural selection. In North America you might think the songbirds in your yard nesting in the Norway Maple are part of a natural scene. But both the tree and many of our songbirds were brought here by Europeans who wanted to “beautify” the new world. Most of the crops we grow here are non-native as well. And some of the species that humans have scattered are so downright unwelcome, such as the fire ant, killer bee and kudzu plant, that we call them invasives. Alan Burdick is the senior editor at Discover Magazine and author of "Out of Eden, An Odyssey of Ecological Invasion." He begins his book with a story of a snake that invaded the island of Guam at the end of World War II.

BURDICK: Fifty years ago, Guam, which is an island way out in the Pacific, had no snakes whatsoever. And then, after World War II, when a lot of wartime surplus was being shipped back to Guam, this snake, originally from Australia, called the brown tree snake, snuck in. And quietly over the course of fifty years it spread and multiplied to the extent that Guam now has more snakes per square mile than anywhere else in the world. And the snake has eaten all the birds on the island, more or less, and fairly radically changed the ecosystem there.

CURWOOD: Tell me a bit about the snake, poisonous?

BURDICK: Slightly venomous, with a bite about the equivalent of a bee sting. In the native range of Australia it is a pretty bit player. It grows to about three feet long and there are a lot bigger, meaner snakes and in fact, its main predator in Australia, things like the king cobra. But on Guam, where it has no predators, it grows up to 12 feet long and it does things that no snake has ever been seen to do before like eat garbage. It’ll eat raw hamburger; it’ll eat the foam plate that raw hamburger comes on. We think of snakes typically as predators, but in this case it’s become a scavenger. I mean, it’s like a rat.

CURWOOD: So how is it the snake shows up on the island of Guam and manages to eat all the birds? How does that work?

BURDICK: This is a snake that’s a predatory snake and it’s placed on an island where, pardon me, the birds have by and large existed without predators for all of their evolutionary lives. So they don’t have the usual kind of evolutionary adaptations to things like snakes, you know, so they kind of sleep unprotected at night and were fairly easy prey. And there really are maybe two species left of the 13 species that Guam once had.

CURWOOD: Now usually though if one creature moves into fresh territory and starts eating something novel, it eats up its food supply and it perishes itself.

BURDICK: Well, the snake eats all the birds. As a consequence the insect population explodes, more insects more spiders. Actually if you walk through the forest these days you don’t hear any birdsong, which is weird enough, but the forest is filled with spider webs. It’s very creepy. So meanwhile the population of lizards also explodes because now they’re eating all the insects. And now these reptiles have become the primary food base for the snake.

CURWOOD: One of the scientists you visited there at the U.S. Brown Tree Snake Research program at one point sets up a camera to monitor snakes. He’s Gad Perry, and, well, why don’t you just read from that section. Could you Allen?

BURDICK: Sure. Maybe I should preface it by saying that Perry and his colleague have set up an elaborate experiment of all these little cubicles, each with a video camera at the top, and in the cubicle each one has a snake and kind of a test set-up with a barrier that they’re trying to perfect against the movement of the snake.

[EXCERPT FROM BOOK] “Perry’s favorite tape is dated April 21, 1995. He slipped it into the video player and fast-forwarded to 9:08pm. A bird’s eye view appeared of cubicle number one, an early test model featuring a one-meter tall barrier with a single electrified wire running along the top. On the floor, in total darkness, Honker, a very large brown tree snake, was considering the possible avenues of escape. The snake crawled up to the barrier and rose onto its tail like a charmed cobra. Its actions might have appeared sinister had the tape not been playing at double speed. Instead the events had a Chaplinesque quality. At last, with its head alone, the snake found purchase on the ledge above the wire and in no time it pulled up the rest of its body, oblivious to the principles of electricity. Earlier when Perry had exhibited cubicle number one with the lights on, he pointed out a piece of masking tape to me that had recently been laid to cover the hairline crevice that runs from floor to ceiling along the edge of the door. The need for this tape was now clear. Stretching over from its ledge, the snake pressed its body against this narrow crack and using an impossibly slim door hinge for leverage, climbed the wall vertically out of camera range. It was at this point the video image began to shake violently. The snake had begun climbing the electrical cable, leading to the camera. Suddenly an enormous reptilian head loomed on screen, out of focus, tongue flicking. The head disappeared, the long body trailed past the camera, the tip of the tail came and went, time 9:17pm. “Well,” Perry said, “we learned from that.””

CURWOOD: (laughter) I guess so. Now you once wrote a piece in Discover, I think it’s probably the seminal idea for your book. It says, “The Truth about Invasive Species: How to stop worrying and learn to love ecological intruders.” I’m sure you’ve gotten a fair amount of flak about that, why do you suppose that is?

BURDICK: There are two important facts about alien species. One of which many of us know and another which is less talked about. And the first one being, you know, we know that organisms like the brown tree snake and the zebra muscle, just a handful of these species, can have very widespread important, expensive impacts and that they deserve our attention. At the same time there are a great many species that don’t have impacts and that’s actually interesting and it’s not really discussed and it’s interesting because it reveals, you know, certain truths about how ecosystems work and don’t work and about our very complicated relationship to nature. I mean, I’m not saying alien species are a dumb issue, we should kind of shrug our shoulders and stop funding policy that prevents their spread. I am frankly just trying to have a little bit of fun, if that’s possible to do with the subject, and say, you know, let’s kind of stop demonizing them and try to understand why these invaders move around, and use these organisms as a kind of a prism to understand the very contradictory demands that we place on nature.

CURWOOD: Towards the end of your book you talk about traveling into space, and one of the most fascinating questions here is about exporting our life forms to other bodies out there in the universe. How difficult is it for us to send a spacecraft to other planets and places without sending our life forms, the little ones I’m thinking of, the microbes?

BURDICK: It is surprisingly difficult. I spent some quality time with a microbiologist at the Jet Propulsion Lab out in Pasadena, and this guy works in the spacecraft assembly facility where they build, well they built the Mars Rovers that are now out there on Mars. And this guy, his job is to kind of inspect what’s left over and to see well, gosh, did any microbes survive the incredibly kind of harsh decontamination process that we’ve devised to get rid of them? And to his great surprise they have, and he’s found at least one microbe that not only thrives in the spacecraft assembly facility, but seems to have actually evolved in it. It’s a tough little spore, it eats aluminum. He found it growing on the surface of one of the Mars Rovers. It forms these spores and then the spores kind of group together to form a little, what he calls an igloo. It looks kind of like a macaroon under a microscope and when he cuts it open and exposes it to the light detection techniques that NASA’s developed to look for life, he finds no sign of life and then when he puts this little igloo back together, the microbe comes back to life amazingly. And I asked him, “So you know you found this thing on the Mars Rover when it was being built. Do you think it’s up there on Mars right now?” And he said, “oh yes, I’m quite certain, I’m almost certain that it is.” So you know, I mean, it’s just indicative of how life wants to spread. Either they’re moving around inadvertently with us or they’re moving around intentionally with us, but they are kind of reflections of our ambition, our desire to reshape the nature around us in a way that makes us more comfortable.

You know, we can kind of demonize these things, but in a way they’re really kind of impressive little critters. They’re sort of doing what nature permitted them to do. And in a Darwinian sense, I mean, they’re winners. I mean you’ve got to be, even if you don’t like aliens, and there is quite a number of reasons not to, I think it’s worthwhile sort of stopping and at least being impressed by their ability to thrive in a world that we think that we dominate. So far as we know, Earth is the only planet with life on it and the wind is blowing outward. We may well be the dandelion in the solar system.

CURWOOD: I was speaking with Allen Burdick of Discover magazine. His book is called "Out of Eden: An Odyssey of Ecological Invasion." Allen, thanks so much for taking this time with me today.

BURDICK: My pleasure, thank you.



“Out of Eden” by Alan Burdick


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