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roundtable:a modern mass extinction Watch Show 3:
"Extinction!" on PBS
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First, a general question. Are we now in a mass extinction, and if so, why does it matter?
Some Web visitors wrote to say they have heard it said, especially of tropical and marine organisms, that we are losing species before we even know of them. And the question is, if we haven't discovered a species yet, how do we know that we've lost it?
Would Darwin support the Federal Endangered Species Act? Millions of dollars are spent by corporations and government for habitat conservation plans, recovery plans, etc., for species that seem doomed for extinction. Is this a wise use of money? Why or why not?
If extinction and mass extinctions are a natural part of Earth's history, should we really be concerned about our effects on endangered species? Are we trying to fight something that's inevitable anyway and that is much larger than us, as a single species ourselves?
I'm concerned with the loss of genetic diversity because it affects food supply, drug discoveries, and the stability of ecosystems on which we depend. And yet, I'm very skeptical of the theory of evolution as it now stands. How does the theory of evolution -- or we could also say that as evolutionary thought -- explain and predict what's going on with the current cycle of extinction, better than if we had to just rely on what we can observe? In other words, what context and what value does evolutionary thought provide to this discussion that we're having?
Several other questions relate to this: Loss of biodiversity, water and air pollution, and the greenhouse effect are all impacting the biosphere, and if these are indeed combining to produce a mass extinction, do you think our species will survive it? Peter's already said that he thinks yes. How about some other perspectives?
Let's move onto some more specific questions. Why do bigger species go extinct faster than smaller ones?
Do you feel that extinctions of large Ice Age mammals had any human causes?
Another Web user wrote: I know there is a gene databank under construction right now. Could this be used as a modern Noah's Ark for the future?
We'll wrap up with a different kind of question. There was one that came from a younger visitor to the Web site who asked, What can kids do to help save the rain forest and animals?


Q: Let's move onto some more specific questions. Why do bigger species go extinct faster than smaller ones?
Panelist Responses: < back to intro page
Daniel Simberloff
Actually, that's not always true. Large birds, for example, on the Pacific Islands have not gone extinct faster than small birds. But I imagine the questioner was thinking of, for example, the dinosaurs or the large mammals that were extinct more recently. And the general reasons that make them extinction prone is, by virtue of their size, they have longer generation rates; often they have lower reproductive rates per generation; and there are fewer of them -- their populations are smaller.

So all of those forces tend to make them more extinction-prone. It's interesting that, in spite of that, in some groups like island birds, there are other forces that counterbalance that. But the general reasons are exactly those: They have smaller population sizes, longer generational times, and lower rates of reproduction.
Ariel Lugo
The other reason is that, if you're being eaten by a predator, you have more biomass per unit catch effect. And if you're bigger, it's harder for you to hide. So all those things lead to extinction. But I agree that small organisms, they are highly affected by some of the habitat modification that we do. You just never know what you're doing, because you don't see them.
Tundi Agardi
It tends to be that the bigger species have more parental care and, as Dan said, they tend to be either slower growing or have a longer life or have a low reproductive rate. So I think species that fit that pattern tend to be more vulnerable to extinction because of those kinds of life history characteristics.
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