JENNIFER LUDDEN, host:
When you hear something's gone the way of the dodo, it means it's vanished from the Earth. Or has it? In recent months, several species thought to be extinct have reappeared: wildflowers in California, snails in Alabama and the South's famous ivory-billed woodpecker found in Arkansas. We began to wonder how scientists decide that a species is truly gone, so we turned to Jim Carlton. He's a professor of marine biology at Williams College, and he joins us from a studio at Yale University.
Welcome, Professor.
Professor JIM CARLTON (Williams College): Thank you.
LUDDEN: Can you tell me what are then the criteria that scientists use to determine extinction?
Prof. CARLTON: It's a difficult array of criteria. We ask about the size of the animal or plant that we're looking for, the habitat in which it lives, the size of the area occupied or thought to have been occupied, and then how difficult it is to search the habitat or the region in general and, finally, how intensive the search has been. And we look at all five of those criteria, a few others as well, and then try to get an assessment as to whether it's probable that we will ever see that species again.
LUDDEN: So it takes more to declare a tiny species extinct because it's harder to find them?
Prof. CARLTON: Absolutely. The smaller the organism, the more likely it is that it could be overlooked in a particular habitat, the more cryptic it is--`cryptic' meaning a species that might be a specialist in a very specific environment, a very specific habitat.
LUDDEN: It must be especially hard to determine if something's extinct in the environment where you work, which is the vast ocean.
Prof. CARLTON: The ocean is often sampled remotely. We use trawls, nets, remote sampling devices. And that often compromises our ability to really establish where species are and how abundant they are.
LUDDEN: With all these formerly extinct species now reappearing, are you still confident in saying that some are definitely never coming back?
Prof. CARLTON: One of the paradigms of extinction science is called HOSPET, `Hope springs eternal.' And so there always is the question of: `Under the next rock, on the next eelgrass blade, in the next cove, will we find that species that has been gone for 50 years or a hundred years?' In some cases, however, we think we have exhausted the known habitat and the known region, but there is always that hope that something will turn up again.
LUDDEN: Can you tell me about your work? I understand you spend a lot of time looking for extinct species.
Prof. CARLTON: Not enough time, by any means. We're concerned with the extinction of marine invertebrates--mollusks, clams and snails--marine crustaceans. It's a search of the world's museum collections and the 19th- and 18th-century literature and then comparing those to what we think is still around today. Some large marine organisms have gone extinct, sort of the classical and iconic species. The great auk, a magnificent bird of the North Atlantic, a bird that stood almost a meter high, last seen in 1844. The stellar sea cow, a very large marine mammal last seen in 1768. Those species, we feel, are likely--are certainly gone, and we've exhausted where they lived and the spatial area they occupied. And these are species that are easily sought out.
At the other extreme would be a small limpet living on eelgrass blades along the New England coast, which has not been seen since 1930. And we searched for it quite a bit from the Canadian Maritimes all the way down to New York and New Jersey, and still it fails to appear.
LUDDEN: In your work, have you ever found a species that was thought to be extinct?
Prof. CARLTON: No. The ones we have identified as gone, I'm still waiting for the phone to ring.
LUDDEN: Jim Carlton is a professor of marine biology at Williams College in Williamstown, Massachusetts.
Thank you.
Prof. CARLTON: Thank you. Transcript provided by NPR, Copyright NPR.
