Extinctions in Madagascar:

A Real-Life Whodunnit

From the Environmental Review Newsletter, Volume Two Number Twelve, December 1995

Introduction:

Madagascar is a California-sized island that separated from the east coast of Africa 165 million years ago. Madagascar has evolved many plants and animals that occur nowhere else in the world; until recent centuries this included some quite large animals: the pygmy hippo, lemurs the size of gorillas, giant tortoises, and half-ton ostrich-like birds. According to the fossil record, humans arrived on the island about 2,000 years ago. Today, Madagascar has no native terrestrial animals bigger than twenty-five pounds. Many of the unique plants and animals of Madagascar are extinct or threatened with extinction, probably due to a combination of human activity and climate change. Paleoecologists such as David Burney study the fossil remains of animals and plants to determine what the climate and ecology of Madagascar were like before and after the arrival of humans.
David Burney received a Master of Science degree in conservation biology from the University of Nairobi, Kenya, where he studied human impacts on the cheetah. He received the Ph.D. in zoology from Duke University pursuing the science of paleoecology - the study of past environments - and is presently an associate professor in the department of biological sciences at Fordham University. Dr. Burney has used microfossils, as well as more conventional archeological and paleontological techniques to study environmental change and extinction in Hawaii, the Caribbean islands, Madagascar, Africa and North America. We spoke with him about what relevance extinctions on Madagascar have to present day environmental concerns.

ER: Dr. Burney, why do you do field work in Madagascar?

DB: Madagascar shows us in the setting of a large island how drastically the environment can change after humans arrive. Over the last decade we have developed information on the ecology of Madagascar going back many thousands of years; and it was a dynamic place: climates were always changing, vegetation zones were shifting about. However in spite of all that animals had to deal with, extinctions seem to have been relatively rare before humans arrived.
     The same pattern has been observed from Hawaii. Helen James and Storrs Olson have demonstrated that relatively few extinctions occurred among the birds of Hawaii over the last hundred thousand years, and then after the Polynesians arrived, more than half the bird species went extinct in a relatively short time. Dave Steadman has documented this kind of pattern in the Galapagos Islands as well.

ER: How do you study the fire ecology of a site 2,000 years old?

DB:      We can get a readout of fire occurrence from microscopic
charcoal particles deposited in the mud. This can show us for instance, that when the climate was dry in a particular place, fire occurrence was fairly high compared to another time when the climate was wetter and the occurrence of fires was lower.
Using techniques of radiometric dating, we can establish to within about a half century the time when a particular event occurred. [Radiometric dating uses radioactive decay of minerals as a chronometer on scales of thousands of years. ed.] Imagine a typical study for us where we collect sediment cores. We drill in the bottom of a lake, or a bog, or the floor of a cave with a hollow pipe and bring up a continuous sequence of the mud or peat that has been lain down over thousands of years. And we can date intervals of the core by the radiocarbon method. In very deep lakes we sometimes see fine alternating light and dark bands in these sediments which represent discreet events, even the changes from dry season to wet season.
     Some of our recent studies are looking at how often fires occur either naturally or under a human regime. You can understand how that would be relevant to forest management questions. For instance, how often a place will burn if there is nobody there to set a fire compared to how often it may burn under different human land uses - pastoralism or agriculture or hunter-gatherer type activities - is the kind of information one needs to determine fire policy today.
     Here in the U.S., for instance, the Nature Conservancy is making management plans for natural areas which in some cases have lakes nearby where they can get this kind of information. This is one of the areas of overlap between what I do - which maybe sounds a bit remote and academic - with land management and the goal of determining what is a natural or appropriate treatment of a landscape.

ER: How do you determine what is appropriate?

DB: We can provide information on background factors before humans or before recorded history. The whole issue of biological invasions is a good example of how paleoecology can make a contribution. The question sometimes arises whether a species belongs in a place or was it introduced by prehistoric people or perhaps introduced in historic times. Fossil pollen analysis is an archive of that kind of information, and we have been able in some cases to address the question: is this plant species native or not, because we can see when its pollen first appears in the record. This can relate to conservation questions or it can be useful to a question an archeologist might have, such as, when did a certain group of people come here, or when did people begin to cultivate a certain plant. So we can sometimes trace the movement of cultures, or humans in general, or a particular land use around the globe on the basis of when a particular plant moved from its native area and began to occur in other places.

ER: Just as we could follow the movement of forests over North America during the last ice age.

DB: This is perhaps one of the most famous examples of this kind of information from paleoecology. Following the last ice age we did not have a coordinated migration of plant communities. The pollen data show that after an ice age, when the climate warms up, each species migrates northward according to its own dispersal capabilities, not waiting for the other species to come along in an integrated system. For instance, in Eastern North America after deglaciation, we see spruces and firs and pines rushing northward, figuratively speaking, in a very short period of time. Because they disperse their seeds on the wind, they spread quickly. Then over six or seven thousand years the oaks show up, the hemlocks and then rather belatedly we see the beeches and the maples. The chestnut appeared to still be spreading northward in historic times, before it was killed off by a blight fungus.

ER: So it took about ten thousand years for the plant community to recover from glaciation?

DB: For everything to get back to its interglacial configuration. Now why is that so important? This information shot down the notion that plants and animals in a community have to be tightly coevolved or linked in some way. It caused the shift to what has been called the individualistic paradigm" in ecology: Instead of nature being reflected in the term "the balance of nature", what is now much more in vogue is the idea that plant communities change all the time; in fact, the idea of a vegetation community having a target climax community is a gross oversimplification of what actually happens.
     This idea can have practical significance because one of conservationists' goals is to restore degraded areas. But if the communities are not tightly integrated, then what specific targets should we have in a particular place? Paleoecology can help answer that question by showing the past range of natural possibilities.

ER: What should conservationists be trying to save then?

DB: If we preserve landscapes, preserve in the sense of making it possible for organisms to move in and out of them and to live there and respond to climate and also to evolutionary pressure, then we are preserving the grand process that will allow evolution and adjustment to climate change to continue. If we get too much in a mind-set of keeping things exactly the way they were before modern man despoiled it - even though that has a great deal of philosophical appeal - if we commit all our resources to trying to do that, we run the risk of losing everything.
     I think the message has come clearly out of the interaction between paleoecologists and conservation managers that we have to preserve the processes themselves and not just the individuals or just a particular community which may be a very ephemeral thing. If we preserve the physical processes, if we make landscapes available for native species to colonize or migrate across in
response to climate change, then we have done our best for nature, in minimizing our impact.

ER: What other tools do use to study past environments?

DB: We are beginning to realize that DNA itself can fossilize surprisingly well under rather special circumstances. Jurassic Park took this to the nth degree but in truth, amber, and sediments that are lacking in oxygen, and dry caves, and rapid freezing events - as we have seen with the Tyrolean ice man - all these places and processes can preserve DNA. And through the use of this chemical fossil, we can learn about the relationships between organisms, extinct or living.

ER: For example?

DB: The U.S. Fish and Wildlife Service and the State of Hawaii have been trying to reestablish some of the endangered birds of the Hawaiian Islands in the wild. The Nene, or Hawaiian goose, is the state bird and yet it almost went extinct. Another very rare bird there is the Laysan duck, which is now found only on one of the small, remote, northwestern islands of the Hawaiian archipelago. In the Hawaiian Islands, wildlife biologists have been spreading the Nene around, putting them on these other islands; the same could be done with the Laysan teal. But until recently wildlife managers were hesitant to do this, since it might be unwise to introduce even an endangered species to areas where it is not native. Well, investigators at the Smithsonian using fossil DNA to make species-level identifications on bird bones they have found on the other islands, have shown clearly that these birds were formerly much more widespread in the Hawaiian Islands. This gives the Fish and Wildlife Service justification for taking some of these birds they have raised in captivity and releasing them in areas of the Hawaiian Islands where they were not known in historic times.

ER: Why did the Nene become rare in the first place?

DB: One of the problems in the Hawaiian Islands is that it is valuable real estate and a lot of places where the Nene would have done quite well are too developed. This did not start with European contact: Polynesians got there perhaps 1,600 years ago, and were quite numerous when Captain Cook arrived in the late 1700's. The Polynesians probably hunted many of the larger bird species to extinction. The other problem is that the Hawaiian Islands are heavily invaded by exotic animals: mongooses, rats, house cats, pigs, goats, these are all big problems in the Hawaiian Islands. I cannot overstress the significance of biotic invasions as a way that humans have changed the course of evolution in many areas of the world. This is an under-recognized problem just about everywhere.
     We tend to focus in on obvious environmental catastrophes like oil spills, and fail to reflect that when you take a longer time perspective, the average oil spill probably takes years or
perhaps decades to clear out of the system but if you introduce a species, inadvertently or intentionally, from one part of the world to another, and it catches on and it becomes a pest there the way rats and mongooses have, you may have caused a whole series of species to go extinct. That is not to minimize the danger of oil spills but to point out the many things humans do that are dangerous for the environment that we do not generally recognize as having that much significance.

ER: How do biotic invasions relate to what you do in Madagascar?

DB: A central question regarding Madagascar is, what has caused the catastrophic extinctions there over the last couple of thousand years. Try to picture a place that had a large animal fauna just a couple of thousand years ago that included seventeen or eighteen large species, a very diverse group of animals: pygmy hippos, two genera of giant birds - ostrich-sized and larger - the whole array of giant lemurs that ranged up to the size of gorillas and chimpanzees; and less familiar animals unique to Madagascar, some of them, like an insectivore - Plesiorycteropus - which has been put into a new, separate order of mammals by Ross MacPhee of the American Museum of Natural History.

ER: It is gone now isn't it?

DB: Yes. It is extinct, but the point is we had a unique, quite diverse megafauna on this island, isolated from other land masses for millions of years and without people until relatively recently. That was presumably the way it was until 2,000 years ago. Today, when you look around Madagascar, all of those large animals are gone. The only surviving megafauna is the crocodile, and the bush pig, which most scientists think was introduced by humans. There are also many endemic small mammals, birds, reptiles, amphibians, insects, and plants. [Endemic species are unique to a location. ed.] It is important to remember that many small animals went extinct as well.
     Likewise we see that a very large area of Madagascar appears to be covered by grasslands that have low biological diversity. Seventy percent of the landmass of the island looks this way. Of course TV and magazines are replete with pictures of the monumental scale of erosion that occurs in the highlands of Madagascar. The question is, how did we get from the one case to the other in such a short time? If humans have been in Madagascar for less time than most other places, how did they manage to have so much more impact than they did in other places? It's a paradox.

ER: How is that a paradox? Didn't the arrival of humans coincide with the extinction of the big animals?

DB: There is a window of time when most of these extinctions occurred between 2,000 years ago and a few hundred years ago, but there is not much evidence for direct human interaction with these animals. Altogether, I can account for only about a dozen
bones of extinct animals that are clearly modified by human tools. In general, there is a pretty good correlation between some of these environmental changes and extinctions and the arrival of humans. Still, the mystery remains because of the rapidity with which the changes occurred and the fact that virtually all large animals went extinct - as well as many smaller ones.
     The extinction pattern is difficult to account for from the global perspective. Look at the adjacent landmass of Africa, and you see the opposite situation. Over eighty percent of the late Pleistocene megafauna of Africa is still with us. [The Pleistocene era starts about 1.6 million years ago. ed.] We still have elephants and rhinos, although we may not for much longer the way things are going, but they have survived into historic times anyway. And there is a whole array of other large animals in Africa, and yet humans have been doing the same things they were doing in Madagascar; that is, slashing and burning and cultivating and hunting and introducing exotic species such as livestock. They have been doing all those things in Africa for a much longer time than in Madagascar and yet there is no strong pattern of extinction.

ER: Doesn't this fit with the idea of island biogeography: reduction of populations below a certain size makes them more likely to die out?

DB: Biogeographically speaking, Madagascar does not qualify very well as an island. In terms of population sizes it is more like a small isolated continent. It is the world's fourth largest island, assuming you don't count Australia as an island. It is large enough that it has continental-level diversity of landscapes and climate. Madagascar spans the Southern Hemisphere tropics, from 12 degrees south latitude to almost 26 degrees south latitude. That is a very large area; bigger than California. In that sense, taking island biogeographic theory fairly strictly, one would not expect one of the most drastic extinction patterns to have occurred there. You would expect that of a relatively small island like Hawaii. But if you look around the world, you find that Madagascar is one of the most extreme cases of animals extinction regardless of island size.

ER: Why do you suspect that the extinctions of the big animals on Madagascar may not have been entirely due to overhunting?

DB: To try to answer that, let me summarize the whole global extinction pattern of the last hundred thousand years in a few hundred words:     The places where humans first evolved - Africa and Eurasia - have had the least extreme version of this pattern of late Quaternary extinction. [Late Quaternary is the last few hundreds of thousands of years. ed.] As humans gradually developed more lethal technologies over a span of several hundred thousand years, one can imagine that animals were also learning the danger of humans. They were learning or evolving to have a longer flight distance from this rather implausible carnivore,
this meager little two-legged creature. It was an important step for humans to develop the ability to strike lethally over a distance, to kill an animal without actually touching it. No other carnivore can do that. So learning that humans were dangerous was probably critical to animals' survival in Africa and Eurasia, and relatively few large animals went extinct in the process.
     Now consider the next case: There was a massive extinction of large animals in Australia about 15 to 40 thousand years ago. There were all sorts of giant kangaroos, and marsupials as big as a rhino for instance. All these animals went extinct leaving only the emu and the four large species of kangaroos we have now. Humans made their way to Australia about 40 to 60 thousand years ago and then sometime later these large animals began going extinct.      Then the next case was the Americas: Humans crossed the Bering Land Bridge from Asia and came into the Americas about 12 to 14 thousand years ago. And within a couple of thousand years throughout the Americas, we had the extinction of mastodons and mammoths and giant ground sloths and saber-tooth cats - the list goes on and on.
     By this time we have either coevolved or eliminated the large animals on all the habitable continents, so now it is time for humans to move to islands. And the first oceanic islands other than New Guinea and Australia that humans colonized were probably in the Mediterranean, so it is not surprising that the earliest of the kinds of extinctions I am describing on islands, appeared to have occurred on Mediterranean islands such as Cyprus and Crete and Sardinia. We get that around 6 to 10 thousand years ago.
     Then in the West Indies, as people made their way across the open ocean to the West Indies about 5 or 6 thousand years ago, same thing: most of the large animals, including rodents as large as bears - if you can imagine a bear-sized rat - as well as ground sloths, insectivores, all have disappeared from the Caribbean islands, although most extinctions there are not dated yet, so we cannot say for sure they disappeared after humans arrived. This was followed by similar kinds of extinctions in the South Pacific islands, spreading across the South Pacific in a way that appears to track with the arrival of humans to ever more remote islands, finally reaching New Zealand, and Easter Island about a thousand years ago. Beyond the South Pacific, people reached the Hawaiian Islands about 1,500 years ago, and Madagascar about 2,000 years ago. When people finally reached these last places, we get the last of these prehistoric, catastrophic extinction events. And so again, no smoking pistol; that is, not much evidence for human hunting, except in New Zealand, but in general, a good correlation between human arrival and the collapse of the big animals.
     The island cases are bad enough, but try to imagine how in the space of a couple thousand years, a few bands of paleo-indians crossed the Bering Land Bridge and killed off virtually all the large species in North and South America with the exception of a few things like the bison, moose and bears. That is a rather sobering realization. If that happened, then it shows that even
without modern technology, humans are capable of incredible biological destruction. How did they do that? Well if they did it, I expect that Paul Martin is to some extent correct with his Blitzkrieg hypothesis. He suggests that it was the naivete of the animals, that they did not recognize humans as posing a danger. By the time they figured that out, it was too late. This is where he gets the notion of a blitzkrieg, of humans moving across the landscape leaving a wave of extinctions in their path.

ER: How long did it take humans to spread out over the Americas?

DB: To get all the way from the northern U.S. to the southern tip of South America, perhaps a thousand years, although there is a lot of disagreement on this point. But when you consider how many kinds of animals went extinct, it is quite remarkable that such a thing could happen.
     To get back to Madagascar. There are some experts who say this blitzkrieg idea is nonsense: There are relatively few historically documented extinctions and most of those are on very small islands, they involve flightless birds or other kinds of relatively helpless organisms and there is not much compelling evidence that a band of aborigines could have come in with stone tools and accomplished such a thing in a place like the Americas. In the case of Madagascar, similarly, we are talking about a group of Iron Age people who were probably not there with hunting as a high priority.
     An old alternative theory for how all these extinctions could have happened, of course, is climate change. I have mixed feelings about this because I have documented a lot of major climate change in places like Madagascar and Hawaii. However, I also believe that climate change in and of itself is an insufficient cause in virtually every case you want to choose, because the climate changed many times over the millennia before these extinctions occurred. True, there were big climate changes going on in Madagascar about the time humans arrived, but it was not the first time that had happened. The difference is, there were many extinctions this time and apparently not at other times. I think climate change was a predisposing factor; for instance, in southern Madagascar, many species were limited by the amount of fresh water available. These animals probably began to disappear fully a thousand years before human impacts are in evidence. But climate change probably did not eliminate many species from the entire island. There is a big difference between a local extinction and a complete extinction or extirpation.
     This climatic theory is still tossed about a bit, but there is another old theory which has been out of fashion and is now coming back: the idea that humans, or some organism that humans may bring along with them like rats, may carry a disease which could reach epidemic proportions in a population that had not been exposed to this disease before and that it would be virulent enough to kill off all these animals. Ross McPhee has recently re-proposed this as a theory for explaining the extinctions. There are a number of things about his theory that some
scientists say is wrong with it. But first let me tell you what is right with it. One thing about the disease theory that is very appealing is it seems to be an explanation for what Ross refers to in a rather literary flourish, as the dreadful syncopation; that is, humans arrive and the animals go out. This is the pattern I have just described throughout the world. It is another way of explaining the trend that does not require invoking some kind of blitzkrieg of human founders killing off naive animals faster than they can learn to run away. Another thing that gives this hypervirulent disease theory a certain kind currency is its emotional appeal. At this time in history when humans are dying from emergent viruses, from AIDS, Ebola, Marburg, and with this new bestseller the Hot Zone which talks about emergent viruses and shows how viruses may jump from one species to another, one cannot help but wonder about past events that look similar. So these two things give people pause before they dismiss Ross's new/old theory outright.
     Let me tell you some things that bother me about it. First of all, it is very difficult to find any examples of diseases that are so hypervirulent that they are quickly lethal across such a wide array of taxonomic groups. In Madagascar, for this idea to work, we've got to come up with a disease that would kill giant tortoises, a reptile; pygmy hippos, a mammal; other mammals that are quite unrelated, such as large primates; and giant birds, such as the half-ton, ten-foot-tall elephant bird. That is a big stretch to come up with such a disease. And where is it now? According to epidemiology theory, such a fast-working killer would be at risk of extinction, too, yet their theory requires that it crop up every time humans move to a new place.
     The other problem is if we use the historic record of exploration, we can look at a few island areas where humans arrived in recent centuries and examine the before-and-after situation for the animals. For instance, consider the Mascarenes - Mauritius and Reunion in the Indian Ocean - where the dodo birds went extinct after people first arrived there in the 1600's, or the Galapagos Islands, which were presumably first visited in the 1500's by humans and have experienced some extinctions since that time. If you look at those two cases, to my knowledge there is nothing in the fairly detailed descriptions of what happened there that says "All the animals got sick today and died." What you see instead is something like, "Today we captured live tortoises and loaded them into our ship so that we would have fresh meat on our voyage home." Or you see that hunters discover in Mauritius that they could set their dogs on the dodos for sport but they comment that it is a pity that the meat does not have a better flavor. That is what you read. Not that all the dodos appear to be sick and dying from some mysterious cause. I think anyone who would want to push a hypervirulent disease theory would have to deal with these kinds of criticisms.
     This points up the extent to which this extinction business is still a mystery and is provoking a considerable amount of useful research. My current approach is to do a good deal of excavation of what I call integrated sites. An integrated site is where you
can excavate and recover a record of the extinct animals before man; and note the disappearance of these higher up in sediment in the same site, and the appearance of various exotic animals such as cows and goats. In the same site we can look at the pollen record and tell what the vegetation was like before humans and what changes it went through naturally and what occurred after humans arrived. And then in the same site again, we can look at the charcoal record and determine the frequency of burning that occurred in the environment before and after humans. In fact, in some areas of Madagascar where we have a long dry season, there appear to have been quite a lot of fires before humans, which makes the notion that fire occurrence alone explains the Madagascar extinctions rather untenable.
     Often, in an integrated site, we can look at the human part of the record. We may find archeological material - pottery, artifacts, even weapons that might be evidence of hunting - that can establish what culture was there and at what time. When we find these integrated sites we get a much richer kind of reconstruction of what went on. When we do this, we find without fail that it was not just one thing in the environment that was going wrong, but a multitude of interacting causes.
     This seems terribly obvious. You may be thinking: why is this big news. It is only big news because it has not been demonstrated before. We know that in modern times when we look at an example of the loss of certain species, we can see several negative factors at work. But what comes out of our research is that this is the typical pattern; this extends well back into prehistoric times. What jumps out at you from this research is that each of the negative things that humans do in an environment tends to feed on the other things they do in a synergistic way. Take for instance, the highlands of Madagascar, this area that today has so much erosion and so few species. Imagine humans coming into a mosaic of environments, some open grassland, some relatively closed woodlands, and with a very diverse megafauna. Some of the fossil sites in this most degraded-looking part of present-day Madagascar had the highest diversity. The irony of this is that fourteen or fifteen different kinds of primates once existed in a place that today supports only cows. If you imagine people increasing the frequency of fires, and opening up the environment and cutting trees, and utilizing the relatively scarce fresh water sources for their rice cultivation and for watering their cattle and therefore driving the animals away from the water, and hunting the animals, and also introducing an array of new species that are much more efficient herbivores, the goat, the pig, the cow; and carnivores, cats and rats and dogs, all of which the local animals might not even recognize as dangerous. Imagine all that going on, while a few centuries or maybe a thousand years before that, the climate was also hitting one of the driest phases in quite some time, so that many species that were water-limited or forest-limited were probably already stressed. All that together adds up to an explosive situation.

ER: Getting a range reduction right when humans show up.

DB: That's right. Each factor amplifying everything else, what we refer to as synergy. Hopefully I am not stretching the point too much when I say that this is a cautionary tale to conservationists throughout the world today in that this is exactly what we see going on almost everywhere now.
     We see human populations expanding. We see lethal technologies proliferating; that is, people are getting guns and chainsaws and bulldozers that never had them before. We see biotic invasion on every hand, new things introduced by humans to places they could not have reached on their own. The most ironic part of this is we also see hints that the climate is changing now, possibly changing very rapidly with human help. So all of these things together are being brewed on a worldwide scale now. There is a rather chilling similarity between the extinctions and range reductions going on now as a global phenomenon and what we have seen time after time on islands and the peripheral continents around the world over the last 40 thousand years.

ER: Can you describe some of the lost animals of Madagascar?

DB: The hardest to visualize are the giant lemurs; they don't look like just oversized lemurs, they look like something you have never seen before. Whereas the elephant bird probably looked like a giant ostrich, three times as big and with much thicker legs. The pygmy hippo looked like the African hippo but scaled down, we suppose.

ER: Has deforestation played a part in Madagascar's extinctions?

DB: Between 1950 and 1985 the forest on Madagascar decreased by fifty percent; a lot of deforestation has occurred in a very short period of time. The population boom came rather late to Madagascar and up until recently, it was rather sparsely populated. Before European contact, we can imagine the people were deforesting some, but perhaps the forest was also growing back in some places. But then as the human population began to explode and technology and demand for wood made deforestation more feasible or attractive to local people, tremendous losses occurred. Forests have retreated almost everywhere in Madagascar to the point where - except for a few large blocks in the east - there are very few forests that have not been cut or degraded. The ones that have not been cut now, are mostly on land that is so steep that it is almost not feasible to cut or cultivate there. A lot of what we see as the cumulative damage to the forests of Madagascar has occurred in the space of a few decades.

ER: Whereas the extinctions occurred long before that.

DB: They started long before that and I think a place where the paleocology message and the conservation message overlap, is that this started about 2,000 years ago and the extinctions that are occurring in Madagascar today are part of the same event. It is not like everything went out 2,000 years ago; a number of these giant lemurs, and probably the pygmy hippo, may well have
survived until relatively recent times. There were what appear to be eye witness accounts of the extinct hippo in the late 19th century, and we have now dated fossils of some of these extinct giant lemurs at only a few hundred years old. So we are not talking about a prehistoric event that is all over and done; this malady is spreading into other taxonomic groups and smaller organisms. It starts with the big animals: the big animals usually have the slowest reproductive rate so they go first. But it has not stopped there. We are now losing bird species and probably reptiles and amphibians; some of the small lemurs are extremely endangered. When you look at Madagascar today, you see this synergy of expanding population, marginal agricultural practices, too much burning, hunting of animals well past the point of diminishing returns, exotic species proliferating - all those things are happening today just as they were happening there before, but on a bigger scale.