Presentation:

Plenary Address

Extinctions, Geographic Ranges, and Patterns of Loss

Stuart L. Pimm, University of Tennessee





Real Audio Recording   

Ladies and gentlemen, thank you for coming this evening to listen to what I have to say. For those of you who live in New York, in a little over two and a half years' time, you will have a unique opportunity, a few blocks from here, to welcome in the new year, the new century and the new millennium. Now, I realize that in an audience populated with academics like this one, there will be some purists who will insist that the new century begins in 2001.

What sort of future will we have in this new century, in this new millennium? I think we are all aware that the human population will reach 10 billion people early on in that century. It could easily reach 20 billion by the middle of it, and even, conceivably, 40 billion by the end of it.

Now, worrying about human future is not new. Thomas Malthus, two centuries ago, was very concerned about the growing populations in industrial England. He was writing at the time of Jane Austen -- Jane Austen has become very popular of late. Much as we may celebrate the life that she wrote about, in the movies that have become so popular, I don't think any of us would want to have lived in the time before electricity, in the time before antibiotics.

So we have this tension between the Malthusians, who worry about the future and the reality of the last two centuries, where there has been enormous progress. So how do we anticipate what the future will be? Should we be optimistic? Should we be pessimistic?

Even if you are optimistic about the future, one has to recognize that there are a large number of problems that we must solve. It's going to be our job to make the next century a good one. If we mess it up, it will be bad for those who follow us. And the particular challenges that we must face are really quite extraordinary.

Primary productivity -- the amount of biological interest the planet produces each year. If you look at the terrestrial primary productivity -- the amount of new green stuff -- we already appropriate 40% of that. The 5 billion people who are on the planet when that calculation was done appropriate 40% of that primary productivity. A third of all marine production goes to support our fisheries. If you turn to freshwater, we already consume 50% of the readily available freshwater on the planet. A doubling population means that all of those figures will become very, very much greater.

It isn't just a matter of averages, either. The productivity -- both in the oceans and on land -- varies greatly from place to place, as does our proportional consumption of it. The consumption of water is even more obvious, and even more obviously a problem, when you begin to think of what happens in the Middle East. Israel, for example, already consumes twice the available freshwater that it has, taking the rest -- the other half that it doesn't have -- from underneath the West Bank and from watersheds in the Golan Heights and in southern Lebanon. Israel's population is going to increase dramatically in the next 20 years, through immigration. The West Bank's population, the Palestinian homeland, Jordan are going to double their population in 20 years; and Syria is going to double its population in 18 years. Because those countries play such a large role in our security, we cannot imagine a safe future unless we address these issues of environmental security, and the flashpoints that our overexploitation of natural resources already represent.

Yet, I find within those challenges nothing that is beyond our technical capacity. There's nothing that we have done there that we cannot, at least in theory, undo. The same is not true for biological diversity. If we have replaced the whale-oil lamp -- the reason why this magnificent beast is so rare is that we needed its oil to light our houses. If we've replaced whale-oil lamps with electricity, we cannot easily replace whales when we drive them to extinction. The process of extinction is not reversible.

So if biological diversity matters to us, and if we are driving species to extinction at unprecedented rates, then we are clearly affecting our future in a completely unsustainable and irreversible way. It's why many of us believe that these issues of extinction and biological diversity are so profoundly important ones.

I cannot go into why I think biological diversity matters to us, but there are three very simple arguments, and they're all compelling. One of them is that there is a simple economic value to biological diversity -- the source of our drugs, of the genetic material for our crops, and so on. There is clearly a value of biodiversity that's there simply because we enjoy it. We Tennesseans, for example, have the Great Smoky Mountains National Park, which is visited by 10 million people a year, who like to enjoy trees rather more numerous than you enjoy here in New York in Central Park.

And, finally, there are important ethical, and even religious, concerns about protecting diversity. Even those who think God's creation is only a few thousand years old join with us in the ecological conservation community in decrying the fact that that special creation is under such threat -- an allegiance, incidentally, which may be politically enormously important to us as we consider reauthorizing the Endangered Species Act in the next year or two.

Given, then, that biological diversity matters, for economic, for aesthetic, for ethical reasons, we ought to be aware of just what is happening to the biodiversity of the planet. And it's that -- a discussion of extinction rates, of past extinction rates, of what we can learn from the material that we've heard from today, that's going to form a central part of my talk tonight. I'm going to move towards what's happening in the future and begin to try and address the question of what we know about the extinction process can tell us about the future, and how we can manage diversity, and prevent those extinctions -- which, I firmly believe, will lead to a poorer human future if we allow them to continue.

This beautiful little frog has a name. I photographed it in the Amazon rainforest about 18 months ago, and even in the middle of that remote forest, we find that there is this vertebrate, and we have given it a name. Climb into the canopy of the rainforest, and the organisms that you find there are, by and large, completely unknown. We know that the vast majority of insects to be found in the rainforest canopy don't have names.

My favorite example of this genre of calculating how many species there might be on the planet comes from thinking about the number of species of fungi. A British scientist noted that there are about six times as many fungi in Britain as there are plants. There are about a quarter of a million species of flowering plants that we have descriptions of, and, therefore, there ought to be about 1.5 million species of fungi in the world. That's an outrageous calculation, and the sort of thing that in any other discipline would not be allowed to grace the pages of even the most mediocre journal -- but you get the idea. There's a million and a half species of fungi, perhaps. We only have names for 70,000 of them, so almost certainly, the vast majority of fungi are undescribed. If you look at rainforest canopies, and you do calculations of how many insects there may be, you easily come up with numbers of 10, 50, maybe even 100 million.

We have names for barely a million species, so we know that there are, conservatively, at least 10, and perhaps 100 times as many species out there than we have names for them. So any calculation of extinction rates are going to be subject to a 1 or 2 order of magnitude -- a 10- or a 100-fold error -- that stems from our complete lack of knowledge about how many species there are on the planet. When you hear numbers like there are 3, or 30, or 300 species going extinct per day, those numbers are actually the same number. It's just a matter of whether you multiply by 10 or multiply by a 100. So, clearly, if we are going to estimate extinction rates, we must use some other measure. We must use some relative measure of extinction that is not so sensitive to our appalling ignorance of the number of species there are out there.

There is another way in which we should make estimates of extinction relative, and that is to recognize that extinctions are part of our geological past. If you have had the pleasure of testifying to such environmentally friendly Congressmen as Young and Pombo and Slade Gorton of Washington, you will know that one of the questions that they are wont to ask is: Well, haven't species always gone extinct? Come into the American Museum and see the dinosaurs. Why should we worry about extinctions when they're so much a part of our history?

Well, let's take a nice slice of our geological past, like the Grand Canyon, and ask an obvious question: What's the background rate -- what's the natural geological rate of extinction? I'm not going to give you a lot of numbers tonight -- I find that they do not aid digestion -- but I want you to remember this one. It's 1 in a million. If you look at a million years of history -- incidentally, that's about 10 feet of the Grand Canyon, I mean, 10 vertical feet, three meters for our metric colleagues -- that's the average duration of a species. If extinctions happen more or less at random, that means that if we took a sample of a million species -- that's about the number of species for which we have names -- we ought to see one of them go extinct per year. And it's that base unit -- one extinction per million species years. Take a million years and look at one species, or take a million species and look at one year. It's that benchmark that I'd like you to remember, because it provides a means of comparing what the recent past, future extinction rates are going to be. And it allows us to compare against the geological past, and allows us to compare for groups that we know, groups that we have good data for these species, and allows us to come up with some relative estimate of what we are doing to the planet's biological diversity.

Naturally, I want to start out in Hawaii. I have to tell you that my research program has public-relations problems. Like many biologists -- like many ecologists -- I go off to Hawaii in January or February, waving good-bye to my colleagues in their white lab coats. It's probably true that I go down the corridors and let them know in very loud voice that I'm going off to Hawaii, and I hope they enjoy their windowless rooms for the next two months.

So I'm showing you this picture to remind you that the Hawaiian volcanoes are very tall -- they're 14,000 feet high. That stuff on the top is snow, and the forests beneath them are wet -- they are some of the wettest places on earth, as much as 30 feet of rain a year -- and all that explains why the students I have working for me, my postdocs I have working in Hawaii, are all British. I can't recruit Californians. Brits, on the other hand, don't know any better, and they're quite happy to go out in the pouring rain and look for rare birds.

I want to start out, of course, with the Polynesians. Hawaii is important, because it is the last place on earth. That's a theme we've heard a lot about today -- the fact that, if we want an experimental test of humanity's impact, we should look at where the bodies are freshest. We should look at where we can see humanity's impact the most recently. Polynesians got to these islands 1,000 years ago, 1,500 years ago, and we have a very good idea of their impact, because of all the fossil bones that we find in lava tubes and other places.

I'm certainly not going to repeat Helen James's talk. I have been a great fan of the work that she and Storrs Olson have done over the years, and Dave Steadman elsewhere in the Pacific. But one of the things that's always puzzled me is: How good a job have they done? Now, I have to say this to the paleontologists in the audience, and with great respect, and as a friend -- you've done a lousy job. You've missed at least half the species on the islands -- and I suspect paleontologists elsewhere have done an even poorer job.

Now, at the risk of not being able to get out of this building alive tonight, let me explain why I know that. We'd like to know how many species we're missing from the fossil record. We'd really like to know how many species the Polynesians exterminated. Helen and Storrs have listed at least 43 species -- not all of them have names -- but there are 43 species that we know are no longer present. We know they must have missed some. How good a sample is that?

Well, all of the species that are present today must have been present 2,000 years ago. We know that there've been no new species created in that short period of time. So the sample we have today, even though it has been depleted by a lot of extinctions, gives us a sample that we can use to evaluate how complete the fossil record is. If every species that we know today was also present in the fossil record, we would know that the fossil record was complete. On the other hand, if only half the species that we know today are present in the fossil record, it suggests that the fossil record is half complete -- that we have missed half the species. And, in actual fact, from island to island, across the Pacific, it turns out that paleontologists have missed about half the species.

As an aside, for those of you who follow behavioral ecology, you'll recognize, of course, that paleontologists behave as optimal foragers -- that they go from patch to patch, collecting specimens. And when the rate of discovery falls to a critical level -- called the "marginal value" in the trade -- they quit and go somewhere else. After all, you gain prestige by describing new species. And if you sit there and collect every last species, your department head will wonder why you're spending his or her money.

So we know, across the Pacific, that the fossil record of fairly well-discovered islands, explored islands, is about 50% incomplete. So for those 43 species, there are approximately 40 other species waiting to be described. I'll be happy to supply suggestions for the names of those species, if you like -- you know, named after some of my favorite people.

That brings the body count to 43 plus, I estimate, about 40 other species gone -- 83 species knocked off by the Polynesians in a relatively short period of time after contact. Europeans arrived soon after James Cook, and we know that they eliminated another 20 species. We know because we have the specimens in the museums. This is the akialoa, one of those wonderful birds with long beaks.

Coming to the present, this is how we are treating our tropical forests in this country. We are knocking our forests down in a completely unsustainable way -- in this case to extract koa wood, which is used for people who carve grotesque images of Hawaiian goddesses and sell the products to tourists in Waikiki for $5.99. One of the species that depends almost exclusively on the koa tree is the akiapola'au -- a species that is so rare that only about 1,000 remain. It's another one of these birds with a peculiar and strange beak.

We also know that there are a dozen species like the akiapola'au so rare that we consider them to be endangered, but not so rare that we cannot find them. There are a further 12 species that are so rare, we are not sure whether they exist or not. My two English postdocs, who have been wandering around in the pouring rain for three years, finally found the po'o uli. They believe there are five left. So there are some species that are so desperately rare it takes years to find them. And when we do find them, we know that we do not have a prayer of saving those species from extinction. Only about a dozen species remain; 11 species remain that are not threatened with immediate extinction.

Put those numbers together and you find, from a total of about 135 species unique to Hawaii, that only 11 are secure. Forty are missing, still to be found by Helen and Storrs's generations of graduate students and their graduate students, and so on; 43 we know from bones; 18 are extinct; 12 we're not certain whether they are there or not; 12 are endangered; and 11 are okay.

If you take those numbers and you do similar calculations across the Pacific -- from Easter Island up to the Hawaiian Islands, to the Marianas, down to New Zealand -- you easily find that there's on an order of 1,000 species of birds that have become extinct in the last thousand of years or so. It may be a larger number than that -- it may be nearer 2,000. Now, there's a number of things that emerge from that simple number. Cultures with only Stone Age technology are capable of inflicting double-digit extinction rates on species. We have lost at least 10%, and perhaps 20%, of our birds in the last 2,000 years to cultures armed with nothing more than stone and wooden clubs. We have much more powerful technology now, so we should not be surprised if our extinction rates will be greater. There is an enormously important lesson here. For those who think that extinction is unlikely, it isn't unlikely -- it's already happened.

Remember I told you that number 1 in a million as a background extinction rate. There are about 10,000 species of birds. If birds have gone extinct at the rate of one a year -- which is the average over the last couple of thousand years -- that suggests that there are about 100 extinctions per million species years. Take the million. You should look at 100 years, for 10,000 birds. That comes to a million species years. You'd expect one extinction in that time -- one extinction in a lifetime, or two lifetimes. In fact, birds are going extinct a hundred times faster than that -- a hundred extinctions per million species years. And that's the past, and that's averaged over a couple of millennia.

All right, so I've made my case for birds. You sit in front of a hostile critic who says: Let's face it, Pimm -- Pacific-island birds are just wimpy. They had it coming to them. You know, why care about anything else? Why do you worry about these birds that clearly weren't going to make it anyway?

This is what my Australian friends would call "miles and miles of bloody Australia." Did I do that reasonably well, Tim? This is the center of Australia. It's a part of Australia that almost no Australians have seen, because why would they want to go there? If you look at the mammalian extinctions over the last couple of centuries, a third of all mammal extinctions have happened here, in the remote, almost uninhabited, parts of Australia.

So, okay -- so it's Pacific-island birds and Australian mammals that are wimpy. Let's look at our rivers. If we look at freshwater fish, we find extinction rates on the order of a few hundred extinctions per million species years in the Mississippi drainage, in the Southwest -- particularly in the east African rift lakes, as the Nile perch invades and wipes out extraordinarily rich assemblages. There are similarly high extinction rates in Southeast Asia. It's not always difficult to figure out what's going on. This is, in fact, Madagascar, with rivers flowing down into the Indian Ocean. This is an ecosystem which is hemorrhaging that sediment that's being washed down the rivers, from areas where the rainforest has been cleared. We have polluted, dammed, channeled our rivers. It's hardly surprising that the extinction rates of fish are globally on the order of a few hundred extinctions per million species years. For groups like freshwater mollusks, the rates are already to the tune of 1,000 extinctions per million species years -- a thousand times background rates.

If you look at plants -- the plants of the fynbos of South Africa -- an extremely rich area with 8.5 thousand species -- and the extinction rates here are alone enough to make the extinction rates of plants -- even if these were the only plant extinctions on the planet -- the extinction rates here are sufficient, again, to bring up the extinction rates of plants to the hundred times background rate. So it's not just birds on islands -- it's birds, and it's mammals, and it's invertebrates, and it's vertebrates, and it's plants. And it's deserts, and it's forests. There is simply no features in those extinction case histories that unite them on the basis of taxonomic affiliation or ecosystem grouping.

What does unite all of those areas is their endemism -- and I'll come to that in just a second. But let me show you one other wonderful survey -- frightening survey, depressing survey -- and that's one done by the Nature Conservancy in their annual report card, the one that they published last year. It surveys the numbers, or the proportions, of species in North America that are on the verge of extinction. It's remarkable because we not only have birds -- we have butterflies and crayfish, and fish, and damsel flies, reptiles -- a whole spectrum of species, 18 different groups. Rather than being wimpy, notice that birds are, in fact, the most robust of groups. Birds are less likely, proportionally, to be threatened with endangerment, to have already gone extinct, than every other group, apart from butterflies.

So when we talk about birds -- and I am going to be talking about birds, principally, this evening -- recognize that we're dealing with a group that is relatively resistant to extinction and endangerment -- not one that is more likely to go extinct than something else. Clearly, these patterns of vulnerability are not unique to particular groups.

This is a plant from the fynbos of South Africa. I normally give this lecture in a much smaller auditorium, about a quarter of this size, and the reason I like this particular species is that I can say that the entire world range of this species would fit into that smaller auditorium. In this particular setting tonight, it would sort of go into this auditorium and leave a lot of room for everybody else.

What unites Hawaiian birds with fynbos plants, with freshwater fish, Australian mammals and the rest of it is that they are species all of which have small geographical ranges. They are endemic; they are found only within relatively small areas -- and in each case the species are rich, or the areas are rich in endemic species. All of 135 birds were endemic. In the fynbos of 8.5 thousand species of plant, a remarkable 6.5 thousand species of plant are found only within the fynbos -- a very, very small area of the Cape Province of South Africa. It's a fact that you have small geographical ranges that predispose a species to be vulnerable to extinction.

I'd like to talk about what I call the "cookie-cutter model of extinction." Imagine a malevolent cookie cutter, stamping out different areas of the planet. If that cookie cutter falls on you, and you are found only within its malevolent boundary, you go extinct. Species that are widespread will not be affected by that; species that are restricted in their ranges will be -- and if you have some areas with a lot of species with very small ranges in one place, then you're going to have a lot of species at risk. It says that this geographical patterning of extinction is what counts.

Let's, with that in mind, begin to talk about the future. This remarkable compilation by Nigel Collar and his colleagues at Bird Life, at Cambridge, list 1,100 species of birds that are thought likely to go extinct in the medium term -- in the order of decades. Another 12% of our birds are likely to go extinct soon. Let's do the extinction-rate calculation on those numbers. Supposing that these 1,100 were the only species that would go extinct in the next hundred years. Many of these species are already extinct -- in fact, the lower bird is the akialoa, which is already gone, and the upper bird is the akiapola'au, which numbers only a thousand. But let's -- supposing that we allow these 1,100 species a century to go -- and no other species go. That works out at 10 species a year, or an extinction rate that is a thousand times the background geological rate.

Those statistics alone tell you that the extinction rate is clearly accelerating -- that the extinction crisis is getting dramatically worse. But I'd like to take another approach to looking at where extinction should take place, because I'd like to know how we should set our international priorities for conserving biological diversity.

And I want to take you back to Hawaii again. When your ecological colleagues disappear, as they do in the wintertime, you will notice that they often go to islands -- particularly tropical ones, of course. And armed with their binoculars and their butterfly nets, and their plant pressers and their mammal traps, and all of the other paraphernalia of our professions -- and they collect species and make lists of them. And, not surprisingly, a small island, like this one, will have fewer species than the larger one, and even fewer than the large one like that -- that's the big island of Hawaii -- all photographed from space.

However, it's not a simple relationship between area and species. If you double the area, you do not double the number of species. Rather, we find there is a particular mathematical relationship between the number of species and area -- and at the risk of giving the mathematically challenged an excuse to leave, let me show you the equation. It says the number of species increases as a constant, c, multiplied by the area raised to a power, z, or zed, depending on your preference for English. The value of z is about a quarter.

What that means for the mathematically challenged is this: Imagine that you are going to reduce an area. You're going to take an area, and you're going to shrink it -- which, of course, is exactly what we do when we destroy habitat. If you reduce an area to 50 -- that's five-zero -- percent of its original area, you will not lose 50% of your species -- you will lose 15 -- one-five -- percent of your species. It's a nonlinear relationship. You can get away with losing a fair bit of area before you'll lose most of your species. Obviously, if you lose all your area, you'll lose all of your species. So the first half of the area you lose, you lose 15%; when you lose the other half, you lose the other 85%. You can use that idea -- this relationship between area and species -- to do just that -- to begin to predict how many species you should lose as you begin to lose habitat.

Let's talk about eastern North America. It's an area whose history we know well. We know that colonists arrived, European colonists arrived, in the early 1600s; spread out from New England into the Ohio Valley; moved into the Lake states; southward, and eventually as far as California. What they did, of course, was to chop the forests down. This is Ohio, looking at a Great Lake in the background. It's wintertime. These are woodlots, and the rest is snow-covered fields. We have created islands of forest in a sea of unsuitable agricultural habitat.

How many species should we lose? Eastern North America has played a crucial role in the debate about extinction. A writer at U.S. News and World Report has suggested that we ecologists do not know what we're doing, because, he said, in an article entitled "The Doomsday Myths," we had chopped down most of the forests in eastern North America, and we did not lose most of our species. It was that criticism that compelled Robert Askins, from Connecticut College and myself to look at the ecological history of eastern North America.

At two scales, we did not cut the forest simultaneously. At the continental scale, there was this spread, this wave of settlers who moved from the northeast ever westwards, so that by the time settlers were cutting the forests of the Ohio Valley, the forests of New England were beginning to recover. People abandoned their farms and let them come back. At the local level, the same thing was true, too. I'm glad that Joel pointed out that I, too, am an American, so I can get away with saying this without generating any more enemies than I have already -- but the early American settles were really dreadful farmers. Their yields were only about a quarter of those of their contemporaries in the Old World. The reason was simple -- labor costs were high here, and farm animals were few, and it was just easier to chop forests down, burn the trees, let the ash enrich the soil, grow crops for a few years, and then abandon the fields to the forest again. The early American farmers were slash-and-burn agriculturists. Mt. Vernon, George Washington's farm in Virginia, was cut, clear-cut, three or four times in its early history. It was cut, they grew crops on it, and they abandoned the fields; they let the forest come back, they cleared it again.

This means that, at the low point of forests in eastern North America, even though we cut almost every last square inch of the continent, at the low point, about half of North America was forested. In 1870, a time when Tennessee only had about 5% of its forests, forest cover was still about 50% for the entirety of eastern North America.

Okay, let's supply that mathematical formula that I showed you: 50% of the area suggests we should lose 15% of the species. How many species of birds are there in eastern North America? There's about 160. Take 15% of 160 and you come up with a prediction of 24 extinctions. Now, from the work of Audubon and others, we know a good deal about what the original bird....

...the ivory-billed woodpecker and Bachman's warbler. It's that discrepancy between four extinctions, and 24 predicted extinctions, that has caused so much contention, so much controversy. It shouldn't. Imagine an experiment -- an ecological disaster. Supposing we reduced all of eastern North America to Ohio. Supposing we cut every last tree, from Florida to Maine to Kansas. How many species of birds would we lose? Well, locally, we might extirpate 160 -- but, in fact, many species would survive in Canada; some would survive in the Great Plains. So how many species are endemic to eastern North America? How many species are found only here? The answer is quite surprising to many ornithologists -- the answer is 28. Eastern North America isn't particularly rich in endemic species of birds.

Now, if you apply that recipe, then, as it should be, to the endemics -- to the species that have geographically restricted ranges, 15% of 28 is a tad less than four, and four is the right answer. I declare victory, until Steven Budiansky and his followers have some very choice rude words. Ah, but you say -- four is a small number. Yes, but it suggests that the recipe should work, so let's begin to apply it on a larger scale. The lesson, incidentally -- the obvious lesson from eastern North America -- is that we ecologists do know how to predict the consequences of clear-cutting forests. But the other important lesson is, it's going to depend on those patterns of endemism -- that only if we learn those lessons can we interpret the ecological history of our country, in the appropriate and correct way.

Let me take you to the Amazon now. This is one of these slides that I feel that I have brought you at great personal risk. It's flying in a small airplane across the western reaches of the Amazon, in a rainstorm -- and I hope you appreciate that. You can see, I think, an area of pale green that has been cut into the mass of the dark green, which is a continuous forest. It's not a great slide, I know -- if you want to go and take a better picture for me, I will be very grateful. I think you can also see in the distance some green scratch marks. That's where roads have been cut.

I want to show you the results of a remarkable study done by David Skole and Compton Tucker, published in Science a few years ago. To orient you, this is the Amazon of just of Brazil. There is the Amazon of Colombia and Peru; Manaos, on the Amazon River, is in here somewhere; the mouth of Amazon is here; way down here is Rio de Janeiro. So this is sort of the bulge of South America. The brownish-looking stuff is a dryer forest and this is the rainforest of the Amazon, the humid forest. The color codes are: white is uncut forest; and progressively darker colors -- progressively redder colors -- are the extent of clear-cutting. There's a little bit of area here -- this is how much forest was cut within the previous five years, and you can see there's a small area here where 100% of the forest was cut. Remember those green scratch marks that I showed you? This is a 16-kilometer, 10-mile-by-10-mile square, that's going to be used as an example, and you can see how the forest has been cut in parallel lines -- roads cut through the forest.

We're going to advance 10 years into the future -- from 1975 to 1985. I find these two slides some of the most startling evidence of our human impact upon the planet. That's what we have done in 10 years. Huge areas in Rondonia and Acre, up in the northeast, all the way around Manaos, along major roads. The satellite evidence is compelling -- it is incontrovertible. We have a very, very good idea of just how fast we are destroying our tropical forests. We have very precise estimates of that.

Okay -- how do we go from these high-tech, precise, continually updatable estimates of habitat destruction to predicting how fast our species are disappearing? Well, the first thing we'd better do is to work out where the species are. My research group and I have gone through the tedious task of digitizing the ranges of all the 2.5 thousand species of passerine bird that occur between Alaska and Tierra del Fuego. The overall patterns of species diversity are well-known, and North America is rather boring -- it doesn't have much. It gets rather more interesting in the tropics. That's why we all go off to the tropics, after all. There's a lot of species, as you'll notice here, in the central part of South America.

But wait a minute -- that's not quite what we want. It's not the number of species on which extinction depends, it's the number of species with small ranges. Now, we can do a little bit of statistical witchcraft. We can take each species and give it a weight, a score, that depends on how rare it is. If a species has a very small geographical range, you give it a high score; if it has a very large geographical range, you give it a very low score. Technically, I weight each species by the reciprocal of the area that it occupies. And we're going to plot those data next.

When you do that, you get a rather different pattern. There's a lot of species in the Amazon, but they tend to be species that have very large geographical ranges. What appears is an extraordinary diversity "hot spot" -- a lot of species with very tiny geographical ranges, occurring along the Andes, particularly in Panama and Costa Rica. But look at this area here -- an isolated area with something like 160 endemic species. It's something that didn't show up in the other map. It's a region of biological richness; it's clearly a region that is particularly vulnerable, because it's small, and it has a lot of species that have small geographical ranges. I want to use this carefully predicted example -- the Atlantic coast forests of Brazil -- for my final test of this idea that we ecologists can predict where extinction is going to happen.

It's the area near Rio de Janeiro -- famous view from cerhado. Turn round, more or less, and look inland, and you'll see a series of mountains stretching inland from the coast, covered in mists. This would have been an area that, once upon a time, was covered in lush tropical forest -- an island of tropical forest separated by a thousand kilometers from the Amazon. Of course, it isn't lush tropical forest -- most of it looks like this: completely barren hillsides, with all the forests stripped off. Depending on where you are in this area, somewhere between 90 and 98% of the forest has gone.

My graduate student, Tom Brooks, and Alan Balmford, at the University of Sheffield, have analyzed this area in some considerable detail. I don't want to go into a lot of those details, but merely to point out a few salient features. We have four subregions within the Atlantic coast forests -- the Algoan slope; the Bahian deciduous forest; inland we have the Aracaria forest. This is how much of the land is remaining; this is the area now over the original area. Two percent for the Algoan slope -- as high as 20% for the Aracaria forest. These are now the endemics -- the species that are found only within those regions. We take that mathematical formula, apply it on the number of endemics, and we predict how many species ought to become extinct as a consequence of habitat destruction.

We then go to the Birds to Watch -- the book of Nigel Collar that I showed you earlier -- and we look at how many species are teetering on the brink of extinction, and that's this number here. If you look at those two sets of numbers, independently derived estimates, you'll find that they are extraordinarily similar. In this incredibly faunistically rich region, we can predict, in detail, how many species are on the verge of extinction.

What I've told you tonight I think is very simple. We are about to enter a new century, a new millennium -- one where our human impacts are going to greatly overwhelm anything that we have seen in our history. Many of those changes are reversible, but the loss of species is not. Already we are driving species to extinction at the rate of 100 or 1,000 times the background rate. The future rates are likely to be between 1,000 and 10,000 times geological rates. Do we know enough to predict where those losses are going to be? Do we know enough to set international priorities for conservation biology?

I suggest the answer is an interesting combination of modern high-tech satellite imagery and an almost Victorian approach to natural history. We won't know the future of biological diversity unless we know what the species are and where the species are. There are few better places to realize the importance of knowing what species are, and where they are to be found, and what we must do to document the patterns of species diversity on the planet than in an auditorium like this one. Thank you very much.

 



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