Ecosystem Management: For a World We Can Live In

The Serengeti: Allometric Herbivores, Charismatic Carnivores, and the Keystone Virus*

by
Dr. Andrew Dobston

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About Dr. Andrew Dobson

Andrew Dobson is an Associate Professor in the Department of Ecology and Evolutionary Biology at Princeton University. He holds a Bachelors of Science degree in Zoology and Applied Entomology from Imperial College of London University, and a Doctor of Philosophy from the Department of Zoology at Oxford. His teaching career started at the University of Rochester in 1986 and he then moved to Princeton in 1990. Dr. Dobson has served as the editor for several journals including Biological Conservation and Natural Resource Modeling. His writing focuses on the population dynamics of infectious diseases and natural populations and the population dynamics in life history strategies of birds and mammals, including work in Yellowstone and in Africa.

 

Introduction

Thank you for giving me the opportunity to go back and put together my thoughts on the Serengeti because although I've been to the Serengeti, I think, at least, once every year since about 1984, I put bits of it together but I'd never been given the opportunity to say, "Well, let's think about the bigger picture." There was an extra line in the talk that should say 'charismatic but lazy' carnivores, but I decided that that might reduce the audience if I cast any expersions on the carnivores. But, as you will see, a perception of carnivores, I hope, changes during the course of this talk. If we go to the Serengeti, we will notice some similarities and differences between the Serengeti and Yellowstone. The entranceway to the Serengeti is less spectacular. It's still a wonderfully similar, provocative experience to past through these gateways. You're slightly more concerned they might drop on your head. You instantly see this sort of vista of the Serengeti and the huge density of wildebeest and other species that are out there. In a poignant way it also reflects the differences between a national park in Tanzania and a national park in the United States, because the annual budget for the Serengeti is probably less than the daily budget for Yellowstone. And although the number of tourists has increased, probably the total number of tourists to East Africa each year or probably the whole of Africa, is probably still less than the number of tourists that visit Yellowstone. So there are big differences. But it does bring in a disproportionately huge amount of money to the local economy. So tourism is crucial, not only to Serengeti, but also to the whole of Tanzania just as it is for other East African countries.

About the Serengeti

Where is the Serengeti? Well, the Serengeti is in East Africa. It's almost on the equator. Just south of the equator. It's a huge area. You could lose several states of the U.S. in there. It's been studied by biologists since about the late 1940s, early 1950s. So we've slowly accumulated a knowledge of the Serengeti. And, in fact, again it was only first visited by people who wrote down what they were seeing at about the same time as Yellowstone was founded as a park. So, we have only really known of it's existence for about a hundred years. Immediately to the south of the Serengeti is Ngorongoro Crater which just as Jackson Hole and the Tetons are effectively part of the Yellowstone system, then Ngorongoro is, in many ways, effectively part of the Serengeti. Though, in other ways, it's its own self contained little system. There are interesting comparisons and contrasts between the two. I've done most of my work in Ngorongoro Crater but it's impossible to resist the temptation to extrapolate up and go and visit the Serengeti each time I go. I have completely failed to resist that temptation. The difference between them is, of course, the Serengeti is huge. Just the feeling of vastness when you visit there. You know you are a very tiny thing when you are in the Serengeti. It's a huge place. In contrast, the Ngorongoro Crater has its own intimacy to it. Even though it's a hundred square miles it's sort of beautifully ten miles across by ten miles across and when you sit on the rim looking down at it, it just perfectly fills your field of vision. So, it's very elegant to look at.

Both systems are dominated by a number of species. And indeed, probably the dominant species in both systems are wildebeest. There are obviously huge herds of wildebeest in the Serengeti. There are large herds of wildebeest in the Crater. Both of these are preyed on by spectacular mammalian predators. Now the relative density of these predators is higher in the crater than it is in the Serengeti. But whenever anybody thinks of Serengeti, straight away their perception is of a coupled predator-prey system where one group of species on the left are in fairly intimate contact with the other group of species on the right. Notice the sort of intense eyeball to eyeball discussion going on here. As with any discussion of this type there's going to be a loser and there's going to a winner. Now, our perception of the Serengeti is formed because of photographs. Those fabulous wildlife films we've seen is that it is a predator/prey system and that's what dominates the interactions going on there. Now, I am going to try to convince you in the course of this lecture, that that's an artificial way we've looked at the Serengeti. And, in fact, there are much more spectacular predators that are slightly less charismatic.

To begin to get a sight of this if we look at one of Tim Carroll's fabulous cheetahs. Here is a really spectacular predator. But that's not what I want you to concentrate on in this slide. If you look at this cheetah, you'll notice it has a very red tummy. That's because these predators themselves are preyed on. There's a parasitic mite--a whole colony, the whole population--a wilderness style population of mites migrating around on the tummy of this cheetah. And while this cheetah is hungry and maybe looking for gazelles to eat, it will spend most of its time worrying about these mites grazing on its belly. If you have had the same thing with tics and things, you will realize that that focuses your attention. And I am going to try to present a case, that if we're thinking about the Serengeti and how we manage it, there are many tiny little things and some much tinier than this mite, that are really important. As important as the big things.

If we briefly look at the history of the Serengeti, it occurs on several different time scales. The longer term geological history, it was formed as the Great African Riff Valley. It's on the edge of the Riff Valley that the crater forms part of the wall of the Riff Valley. As that slipped down, it created a series of volcanoes whose explosions created the plains that are the Serengeti. And, curiously, that series of explosions occurred at roughly the same time that the series of explosions that created Yellowstone occurred. We're talking close to 5 million years ago. But I find it sort of ironic that the two areas left in Africa and North America where there are huge densities of wild mammals, are both areas that were violently disrupted 5 million years ago. Not that we want to do the management experiment. We are doing that. It's also an area wherein intrinsically humans have always been part. Since we have always been part of it for those 5 million years, because what separates Serengeti from Ngorongoro is Olduvai Gorge, our scientific perception is that it is very close to the area where humans evolved. So humans have always been part of the Serengeti since that volcanic eruption that set it up. So, humans are a intrinsic part of this process. And to try to ignore them would be very silly.

Scientific Research and the Serengeti

Now, a second type of human arrived 5 million years after the big explosion. That's the year scientific research began, and the first people to go there were the Grzimeks. Sort of father and son team who went there as part of a Frankfort Zoological Society project, to see what was going on in the Serengeti and indeed wrote a very evocative book about the Serengeti. There were two beautiful books written in the early 60s about it. The reason the Grzimeks went was, of course, the Serengeti wasn't in Tanzania then. It was in British Tanganyika. The British government had decided "oh gosh, there's this large plain that's full of animals eating. Wouldn't it be good if we shot all the animals and turned it into a cattle ranch?" A debate in British Parliament occurred in 1954, that it might be a sensible thing to shoot all the animals in the Serengeti and turn it into a big cattle farm because, and this might seem even more bizarre, the British government was very worried about whether it was going to maintain its interest in Argentina and whether that would supply a source a beef for the English Sunday lunch.

But, the reason the Grzimeks went out there was to say this is such a spectacular wildlife phenomenon that we don't want the British government to do this. And they drew the world's attention to Serengeti as a natural phenomenon. As did another character, Henry Fosbrook, who at the same time went and worked in the crater. Henry is still alive, deeply eccentric and a wonderful person to meet if you can drink that much scotch. This drew the world's attention to the Serengeti and researchers started going there. And indeed, there's been a wonderful history of research in the Serengeti, despite the sort of complications of working there, particular in the 70s when it was essentially cut off from its borders with Kenya. Partly because Kenya kept sending out posters saying, come and visit the Serengeti in Kenya, so everybody would go to Kenya and then discover it was in Tanzania and all the tourist money went to Kenya rather than Tanzania. So the Tanzanians said if you go to Kenya you can't come to Tanzania, you have to directly come to Tanzania. And since she closed down the borders for 5 to 10 years. Despite that, the hardy ecologists got through and there have been two wonderful compilations of research. Serengeti I and Serengeti II of which Tony Sinclair has been a marvelous motivator drawing everybody together. Trying to get people who lived closely together to actually sit down and work together is a task that you'd be better off going and wrestling the lions and hyenas. Tony managed this. There has also been a whole suite of scientific papers. Some of which everybody has read. Some of which nobody's read.

Now, you can go to somewhere spectacular like the Serengeti surrounded by lions, zebras, wildebeest and do the classic sort of thing that an ecologist does. Here is an ecologist at work. He's in the middle of nowhere. He's thrown down his cordrack and he's looking at the grass that's growing in it. A lion could come up and eat him and he probably wouldn't notice. He's busy collecting data. What is he collecting data on? He's collecting data on the thing that is fundamental to the way that the Serengeti works and that's "how rapidly does the grass grow?" What are the major things that drive the Serengeti? That's plainly two things. One is rainfall. There's a distinct rainfall grading across the Serengeti from the Crater in the south, where we are up in Highlands at 6-7 thousand feet (lots of rainfall), through the short-grass plains where the rain drops dramatically, and that increasing amount as you go down towards Lake Victoria in the west or up north towards the Massi Morra, the small part of the Serengeti that sticks into Kenya. That gradation of rainfall creates a gradation in the amount of primary productivity, the amount of grass growing in an area. That means that the amount of food that's available to eat is different in different parts of the Serengeti. Although there are differences throughout the year, to a rough approximation, the animals occur where most of the grass is. Shock, horror. People go to places where there are restaurants. Animals do the same thing.

Rainfall, Primary Productivity, and Population Dynamics

Now the fabulous studies of Sam McNaughton. I really feel Sam could have done a much better job of giving this talk because Sam has done such fabulous work there. If you look at Sam's studies, he's shown certainly across the Serengeti and across years, there's a very powerful relationship between the amount of annual rainfall and the amount of primary productivity. More rain, more grass. There's also an increasing relationship between the amount of grass produced and the amount eaten. And indeed, if you go and sample different sites, where Sam has gone and set up little exclosures and asked, "what's the amount of grass produced in the exclosure in the course of a year and what's the amount actually eaten?" There you see something that's spectacular. The mean amount of primary productivity actually eaten in the system is of the order of 80-85%. And there are some areas where the amount eaten is 90-95%. There are other areas where it's close to 20%. If we go to Yellowstone the amount eaten is of the order of 40-45% where Sam has done analysis studies as have other people. If you think Yellowstone is overgrazed, then certainly the Serengeti is massively overgrazed. But each year it bounces back and you get this massive primary productivity. It's not necessarily overgrazed. Providing there's enough rainfall it's always going to bounce back. Notice also there's a relationship between where the productivity goes and the proportion. If it's eaten in the areas where productivity is higher, a much higher proportion of it is eaten. Then indeed this creates another effect that characterizes the Serengeti; that for many species they might graze around the ecosystem during the course of the year. So they are essentially following the areas of highest primary productivity, so you get this massive migration of the wildebeest.

This is the thing that the Grzimeks went to study. And the Talberts went to study. And showed that there was this regular annual cycle of movement of the biggest biomass of herbivores following the grass production around. Similar things happened in the Crater. You don't have the large scale spectacular migration but during the course of the year, the herds of wildebeest that are in there, make their way around the lake and up onto the shoulders to areas where increasing productivity is occurring. Superimposed upon that is the second effect, that depending on how tall the grass is, different species are able to eat it. There's a classic little monograph produced by Mazey Fitzgerald which is very much a book of the late fifties and late sixties. It assumes that nature is wonderfully helpful to each other. It's sort of the Lord of the Rings of the Serengeti; pointing out that the elephants are really nice to the buffalo because they graze down the heavy vegetation and make it available to the buffalo. The buffalo are then very altruistic towards the zebra, they graze it down so as the zebra have food. The zebra graze it down so as the wildebeest then have a nice meal and the wildebeest graze it down so as the Thompson Gazelle got a nice meal. Everybody is helping each other out. Very sixties in its way. But of course, it then gets dismissed because although this process is going on and you can go and see this sequence of species going through every patch of vegetation, evolutionary that's not a sensible long term strategy. So, why does this type of affect occur?

Well, to understand that we have to understand something about the way these animals feed and the way their populations are related to their feeding. How is that coupled to the resources available to them? To get at that, I'm going to talk briefly about the way that primary productivity is linked to food consumption and how that affects the population dynamics of the species. To get to that, I am going to do something that I think we should do more of in studies of ecosystems [in that we sometimes know about the population dynamics of one or two species but we usually don't know anything about the population dynamics of most species]. If we go to evolutionary biology we know that the dynamics of different species scale alometrically with their body size. So if we are stuck with the diversity of species in ecosystems, can we do the population dynamics of the species we don't know by scaling everything alometrically? Which maybe is wishful thinking but, oddly enough, it begins to get us a long way.

So let's just think how we would do this. And it takes us one step further to the other things we want to do, if we want to think at all about managing these populations. Because always if we are interested in managing a population--such as elk in Yellowstone, wildebeest in the Serengeti, buffalo in the Serengeti--we need to understand something about its population dynamics. And the traditional way of doing that has been to collect long term data to estimate the survival rate, the fecundity and then try to work out either what's this magical thing 'carrying capacity' or what is the density dependence in that population. How are birth rates linked to population size. And, increasingly, that's what fishery scientists try to do. That's what wildlife managers try to do. But we keep coming unstuck on this as a paradigm. It's crucially important to be able to do it in the Serengeti where increasingly there's poaching and, just as in Yellowstone, this pressure for people to start hunting again. We need to know what sort of levels of hunting we can take or how much we have to control poaching.

Here we see an anti-poaching patrol out. Poaching isn't done with guns. It's essentially just done by putting out traps, snares, and animals are caught. They eventually just suffocate or die and people come along and collect the meat later. Now, you can try to work out the relationship between the relative population of buffalo in the Serengeti and the amount you can remove and what level would be sustainable. Just as we could do this for elk or we could do it for wildebeest but we would always be searching for this mythical dependence thing which is there but hard to quantify. It also, more importantly, ignores the relationship between the buffalo or the wildebeest or the elk and the primary productivity. So, is there some way we can link those two things together and therefore, not only understand how we might manage these populations, but also understand how the ecosystem works? Because if we ever really want to manage it, we have got to understand how the different components are coupled together.

Now we can easily set up a little thing that says we know how rainfall turns into grass; let's have a little computer simulation where we have rain equal to the sort of variability of rain we see in the Serengeti producing grass like the grass we see in the Serengeti. That's a really nice easy thing to do. We then want to know something about how that grass is eaten by a wildebeest. Now, curiously, if we do this allometric scaling, we know the total amount of food a wildebeest needs to eat per day. Therefore, we know the amount it needs to eat per year, so we know where that curve settles. We know the maximum amount of food a wildebeest can eat per year. Now, if we could estimate that, we could then say we know something about the rainfall. We know how much vegetation that produces. We know how much we need to feed an individual wildebeest, and as we have more rainfall, we would expect to be able to feed more wildebeest. So, by allometrically scaling in this way, we can find some relationship between rainfall and the number of wildebeest we would expect to be able to support.

Then you can extend the things that Mark [Boyce] mentioned that Graham Corley had done. Towards the end of his life Graham went back and revisited these things and said, "Let's really couple vegetation to rainfall and revisit herbivore plant models." This variability in the rain produces variability in the vegetation. We introduce a few herbivores, their dynamics are much more stable that either that of the grass or the rainfall, but they settle down to a density that we would expect for that amount of rainfall. We then say, that's good. We have done it for one species, let's try and do it for lots of species; Thompson Gazelles, wildebeest, zebra, buffalo. We work out what their functional responses are. We put them all together in the vegetation and what we discover is that only one species can be supported by one type of vegetation. So we try to put together an ecosystem model and it's failed miserably. That's annoying. This is similar to a simple economics problem; whoever is the best at acquiring the vegetation and using it is always going to beat out the others. So this says if you just go in in that simple minded way, you can't have co-existence of all the herbivores. One will always win. Now that's a bit sad because to really understand the ecosystem, we want them all coexisting. Is there something else going on? Curiously, there is a really interesting effect referred to by Masie Fitzgerald and inherent in grazing succession. If you look--and this is something Andrew Illious does--at the height of grass in any area, then there's a minimum height that an animal of a different size could graze down to. In a sense, the bigger you are, the bigger your minimum grass height.

Now, we know that grazing succession says you go from large animals down to small animals, so if big animals are grazing the grass down to where it's no longer efficient for them to eat it, they accidentally create a resource for a smaller animal to come and eat it. Indeed, we can look across Africa and show for all the African ungulates that have ever been looked at, there's a relationship between rainfall--which is creating grass of different depths--and population density whereby each of those species require a different minimum amount of rainfall or a minimum amount of grass before they can start feeding, or establish. So there seem to be thresholds determined by the amount of rainfall, which is probably functionally determined by the size of the animal feeding on them. This means that essentially a graph of feeding response is shifted to the right. It doesn't start at zero. You have to have a certain amount of vegetation before you can start feeding and that curve then grows up there. Now, when we do that, we can put together our community in a slightly different way because each of the species will start progressively to the right. So the very small species will have a little patch where it can maximize its food and nobody else will be able to establish. Another species can then establish. It then will out-compete the smaller species for food. Thirdly, another species established and, eventually four and five and you can add them on.

That begins to tell you something very deep about the way the Serengeti herbivore community is structured. It says that effectively if the vegetation is all the same--which it isn't, something might come in it--it's still possible for a large number of different herbivore species to coexist on that if they all have different body sizes. Because they will all utilize grass of different depths and, eventually, graze it down to others. In fact, those who are using the biggest depths will have to keep moving around whereas those that use it at the smallest depths can probably stay in the same place. And indeed, that's roughly what we see in the Serengeti. The Thompson Gazelles stay on the short grass plains and some of them follow around the wildebeest. The wildebeest and the large animals, the zebras, have to move around over large areas, eating down the vegetation to where it is no longer economically viable to eat it and then they move off to another area. So you get the whole grazing succession in there. All those species can coexist and they roughly settle down to the densities we actually see them settling down at. And of course, differences in relative body size will determine differences in relative density as will differences in relative rainfall producing the vegetation.

So we can extrapolate beyond the Serengeti to other areas in Africa and get some predictions of what the biomass of the community is and what its composition would be. That's quite an important result. And indeed you can recover these relationships that have been found several times in the literature; as rainfall increases, the biomass supported by that rainfall increases and the diversity of it also increases. And, in fact, you could also predict the species composition. So that's telling you a lot about the two primary components of the ecosystem--the herbage that's there, and the species, and the species diversity supported by it. Now, that oversimplifies the vegetation and, indeed there's a variety of species of grass in the vegetation. There's a certain amount of differentiation--certain species of herbivore feeding on certain species of plants--but the plants are all growing together. What you do find, very importantly, is the more diverse the vegetation is the more rapidly it recovers from grazing. So the speed at which the grass recovers from being grazed by the species is strongly a function of the diversity of grass species. That's a strong argument for maintaining a diversity of grass species. In many ways it's a direct analysis result to the one David Tilman sees for grasses in the Midwest--the more diverse a prairie you have, the more rapidly it responds from the drought. Occasionally, you will get a really bad drought and our worry with El Nino is that you will get much longer droughts than we've had in the past and in some areas may begin to get heavily overgrazed. This is Amboseli a couple of winters ago when it was incredibly down to almost bare earth. Curiously, even though it was heavily grazed it still bounces back and you can go back six months later and there's eight to ten inches of grass there. It has an amazing ability to recover. You just pour water on it.

The Role of Predators

What does all this imply for the predators? Because the predators are there they eat the prey. As I said, our perception is that we have a system where the predators are controlling the prey. Is this in fact the case? George Schaller was, perhaps, the first person to go there to study the lions. There was also Hans Crook studying hyenas at the same time. The lion study was taken up by Ambian and Bentbiger and since then by Craig Packer and Ann Pease. If you look at lion predation, it's a wonderfully spectacular event whenever you see it on TV. The lions come in and they all seem to be organized chasing the prey. When you actually see one in the file, it's somewhat different from that because you can't cut and edit. This female lion has caught a wildebeest. I'm sitting in my Land Rover and I've been lucky enough to see it. Twenty minutes later she has fallen asleep but she's been joined by another lion who is still trying to knock the wildebeest over and a third lion has noticed something going on. If you go back and read Shallow's account, there are these nice graphs that say a very small proportion of lion hunts are successful. They really are not great predators. They really are quite lazy. In contrast, the predator that is very spectacular are the hyenas, whereas everyone's perception is that they are lazy, and that they parasitize lion kills. In fact, it's very much the other way around. As you might expect in a matriarchal society, the hyena females do a huge amount of work. They commute over vast distances. Some of them 50-80 miles a night, going off hunting, bringing food back. If anything, the lions parasitize hyena kills. Because the lions are bigger than the hyenas, they can get in. So the hyenas kill things very quickly and then run back 50-60 miles with their food.

However, if you look at long term data from the Serengeti, particularly data on the wildebeest herds, it's dominated by a particularly dramatic effect. Since people started studying the wildebeest in the early 60s, the numbers increased rapidly from about a quarter of a million­which at the time we thought was a spectacular density­up to about one and a half million. There then has been a slight decline. Now, if predators are controlling that population they are not doing a particularly good job. And indeed, what also happens at the same time is that the predator population has increased because there's more things for them to eat. That suggests very strongly to me that the predators are not controlling the prey. Just as the amount of grass determines how many wildebeest you have, the amount of wildebeest and zebras you have determines the number of predators you have. So what is causing this affect? Well, there's a wonderful study of the wildebeest done by Lee and Martha Tolbert in the 1960s. Their study said that if you looked at the total mortality in the wildebeest population, you could divide up what was happening to the adults and juveniles. With adults there was a certain amount of predation and there were huge amounts of accidents when they are on migration, particularly when they cross rivers--they keep tripping over each other and drowning. That's a major source of mortality for adults. In contrast, if you looked at juveniles, some mortality is predation but most of the mortality back in the 60s was due to an infectious disease which they called yearling disease. We now know that that disease was a thing called Rinderpest. Now probably everyone in this room has been exposed to a close ancestor of Rinderpest. It's is the ancestor of measles. It's a mobilly virus. And the mobilly virus is probably one of the biggest killers in history. They evolved over the last 5,000 years. A big split occurred between Rinderpest and canine distemper which is also a mobilly virus. Probably when we started domesticating cats and cattle, dogs and cattle at a similar time. As we grew more familiar with cattle, measles evolved which goes into humans.

Rinderpest

So you have this suite of things that are monster killers. What happened to them in Africa? Well, the Sahara had effectively isolated southern Africa from Rinderpest. There were Rinderpest epidemics we know historically throughout Europe and India. It wasn't introduced into Africa until 1890. Shortly after people started opening up East Africa as a place to live, it swept from the horn of Africa, where we think about five infected cattle were introduced, to the cape over the course of twelve years and probably killed between 80 and 90% of the game in Africa. The present geographical distributions of many species still reflect that they haven't recovered from the Rinderpest epidemic. The few descriptions we have, which are written diaries from explorers, would recall that the plains were just littered with carcasses. The vultures couldn't fly, they were so full. It must have been a real horror and, of course, it was a major constraint on the establishment of the cattle industry as well as having a big impact on the game species. Now, a totally brilliant and wonderful guy came along in the 1950s and developed a vaccine for Rinderpest. [Really a wonderful guy called Walter Plowright, still alive. It's a major sort of plug--if you want to live for a long time, the evidence is you should work on viruses. All the people this century who have worked on animal viruses are still alive and kicking and active in their 80s and 90s. Plowright, Frank Fenner. It's a real good thing to do for your health. Probably you surreptitiously immunize yourself to the things that might kill everybody else.]

The vaccine allows us to do a wonderful experiment on the Serengeti because you can vaccinate everything against Rinderpest. You don't vaccinate everything. Part of the British government's argument for clearing the Serengeti of wildebeest was that the wildebeest were perceived to be a reservoir for Rinderpest. I mean this is brucellosis in Yellowstone all over again. We have to go in and kill all the wildebeest so we can establish a cattle industry. So, Walter develops a vaccine. Nobody is going to go out there and jab a quarter of a million wildebeest with vaccine. Nobody is going to go out there and wrestle with wild buffaloes and do it. Let's start with the cattle and protect the cattle industry. So each year, they would go out, they still do this every year in different parts of the Serengeti, and vaccinate all the cattle in the area. As high a proportion of them as possible. What does this do to everything else? By just vaccinating cattle, Rinderpest disappears from all the other species in the ecosystem. Well, it's quite a remarkable and wonderful thing that they [British bureaucrats] do from my perspective. Throughout the world there have been British bureaucrats demanding that whenever anybody has done something interesting scientifically that the results be written down in ledgers somewhere. And the British government demanded that every cattle vaccinated should be counted and written down in a ledger somewhere. So we have all these data back to the 1950s when it started so we can actually spatially look at this vaccination program. Now what does that do to a hypothesis that wildebeest are the reservoir for Rinderpest? Falsifies that wonderfully.

Modeling the Serengeti

What about all the other things that are there? We attempted to try and understand this, in the second book when Tony Sinclair invited along Ray Hilborn to get all the biologists who worked on the Serengeti together, to have a meeting where we all gave our dog and pony shows. We all talked about our research and we tried not to bite each other, because there were some disagreements. What Ray did was to say, "Okay. Now, I want to take everybody's expertise and with Andy's help on the computer, we are going to make a model of the Serengeti." And, of course, everybody went, "Oh, God. You can't conceivably do that." But, essentially, there were two points to the exercise--one was to try and make a computer model and the other was to try and look at what might be important in the long-term management of the ecosystem. And it was a wonderful parody of what it would be like if you brought biologists together to try and do this. Half the people there had worked on the carnivores and said things like, "you couldn't conceivably extrapolate from what Simba's group does to what Mowgli's group does." And we said, "well, that's okay because the lions don't do anything important anyway. They're just there for the tourists to photograph."

And then there was nobody at the meeting that brought anything on insects. We know nothing, really, about insects in the Serengeti. There are 100 species of dung beetles, from incredibly tiny to things that are as big as golf balls which, if one hits you on the head when you're driving along, you realize the insects have a role to play in this system. They remove all the dung and they move the dung about, and recycling that dung is an important point of where things go and feed. We really don't know anything. One person has studied insects in the Serengeti in the last 25 years--no, two people have. It's a fantastic diversity of birds. There are more bird species in the Serengeti than there are in the entire U.S. We know vultures tidy up after everybody else. They sort of have a recycling garbage collection role, but the other species, we really haven't had a lot of studies on them. This points to nice things that graduate students could go and do.

We know that fire is important in the Serengeti ecosystem. I haven't touched on it. There's some fabulous studies by Neil Stronik. There are times when you can visit the Serengeti and it seems the whole place is on fire. It looked as dramatic as Yellowstone, but it bounces back again. It's very resilient, but fire plainly plays a role in the relative amount of open habitat versus Miombo bush habitat. There may have been a role for elephants, and then there may be a quite subtle interaction between elephants, fire, and the sort of boundary between bush land and grass land. Because the elephants have been so heavily poached, we'll never really know. They're beginning to come back in the North, and all of the studies on the interactions between elephants, fire, and bush land have been done in the North. But we still don't really understand what role elephants play, and we have no hope of ever understanding what role rhinos played. The population of rhinos when the Grzimeks first went there was up in the couple of thousands in the Serengeti. There are now 5--I think we're up to about 16--the only place you can find them is in the crater. Just a crater being isolated the way it is, it's one place you can protect them. So we'll never know what role they played, if they played a role at all.

The most crucial other organism in there still remains humans. Although, a few people live in or around the park, part of the controversy of setting up the Serengeti, and a sharp contrast with the Ngorongoro Conservation area, is that humans were effectively removed from the Serengeti where they were allowed to remain in Ngorongoro as part of the system. If you look at the Serengeti now, there are people living right up to the boundary of the park. Back, where the green starts is the boundary of the one Ngorongoro Conservation area. If you just look at the increase in human population around the West side, the human population there is huge. And, sure, all of those people have to live, but increasingly people are living by poaching, and that has to be a consideration in how we manage the park. How do we control the poaching? How do we manage it? Should those people be allowed to use the wildebeest in the park as a source of protein? And that's a very hard problem to address in a country where a too good approximation is most people are starving.

Conclusions

So, the conclusions. We barely really have looked at the Serengeti over the last 30-40 years. How it works depends on our preconceived opinions. And as an epidemiologist, plainly I've promoted the fact that the most important thing is a pathogen, because that's my preconceived opinion, but, I have no doubt in 10 years, 20 years time we'll see that from a different perspective. Maybe a different pathogen will come in, maybe the predators will get off their backs and do a better job of regulating things. If we really want to understand it how do we do the next scientific studies? I still always worry at the back of my mind whenever policy is mentioned; I remember, the best summary of policy was J. K. Galbraith, who said that "policy is formalizing the trivial." Our role as scientists should be to show that science has a crucial role to play in policy, and that, unless we understand a thing scientifically, we can never make any sensible scientific policy. All we do is talk about things and 'formalize the trivial.' Perhaps, this allometric scaling will help us to dissect out how the system works, and an interesting thing is we can apply similar techniques to understanding how the disease works and is transmitted in the system. So, it does create a powerful set of tools for solving these big problems if we haven't got enough people to work on them, which are much harder than the problems the so-called rocket scientists have worked on. They're much deeper scientific problems. It's been easy for them to get money for what was perceived to be a big part of our future of democracy. To me, understanding how ecosystems work and having scientists understand that is still the crucial thing we've got to do.

The other thing is, it's ridiculous. We know the Serengeti has been there for five million years. We've only looked at it for a short time. Literally 30 or 40 years. We really don't have a deep perception of how it works on a long time scale. We've seen a very, very small snippet of it. Everything could be put into this concluding slide, or almost everything. It's essentially, if you look at it, an interaction between the local people with their cattle, who increasingly place pressure to move into the park, and the parks. This is the lake in the Ngorongoro Crater. There's always the possibility for disease transmission from wild animals to domestic animals, but there is as big a problem of disease transmission from domestic animals to wild animals. There are tourists bringing in huge amounts of money, a sort of second species of humans in the park, that bring in lots of money. Do you want these people to turn into a tourist facility or do you want them to maintain their normal way of life? And that's a very important management consideration that's hard to put into simple scientific terms. We need to stand back from Auchim's razor and apply this shaving foam of sociology.

I go into the Serengeti every year and when I look back there are just hundreds of people who had to be acknowledged for different reasons, but particularly, Dan Rubenstein and Nick Jordeodis, for first taking me. The wonderful group of Tanzanian vets and wildlife biologists I've worked with, Emanuel Josie(?). Emanuel has worked with everybody in the Serengeti right back to Mazie Fitzgerald. He's just a wonderful person. People whose ideas have turned into my way of thinking about the Serengeti and then just the people I've been there with who have changed my way of life; nearly got me arrested, stopped me when I nearly died, etc. The Serengeti has changed my whole life and it would be nice to put something back into it. The crucial way to do that is, of course, to try and teach the people who live there now what a wonderful thing they have and to try and find ways for them to manage it. This is a little guy [slide] I met in the Serengeti who was worried about me being near his cattle, so he came to point his spear at me, but I offered him a pen. He had never seen one before. But we still have to work out how we train and develop a discussion with this guy on how we manage something that's much more his than it is mine.

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Dobson, Andrew. The Serengeti: Allometric Herbivores, Charismatic Carnivores, and the Keystone Virus. Presentation given at Symposium "Ecosystem Management: For a world we can live in." September 25, 1997. University of Michigan, School of Natural Resources and Environment. Ann Arbor, MI.

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