Ep 72: Stability and change: Lessons from the Serengeti (with Tony Sinclair)
Why is the Serengeti such a special ecosystem? Why does it support so many different species, and what ecological processes regulate the enormous population sizes of its dominant large-bodied herbivores?
On this episode, we talk with Tony Sinclair, professor emeritus of zoology at the University of British Columbia, about his new book “A Place Like No Other: Discovering the Secrets of Serengeti”. Since the 1960s, Tony has studied the bottom-up and top-down processes that regulate wildlife populations in the Serengeti. We talk about how he discovered the major rules of regulation, the unique geography and climate of the Serengeti, the major forces driving wildebeests on epic annual migrations, and the roles that elephants play in stabilizing ecosystems into alternative stable states. We also talk with Tony about the controversial topic of rewilding degraded ecosystems. Tony argues that effective strategies for rewilding emerge only from understanding the fundamental processes that shape ecosystems in the first place.
Cover photo: Keating Shahmehri
-
SPEAKERS
Tony Sinclair, Art Woods, Marty Martin
Art Woods 00:00
Before we get started, we'd like to thank our Patreon supporters and remind listeners that as a nonprofit, we rely on your help to keep making the shows you love. To support us, please consider making a monthly donation through our Patreon page at patreon.com/bigbio, you can also make a one time contribution at bigbiology.org.
Marty Martin 00:17
Another way you can help us is to recommend Big Biology to a friend or classmate or professor, and spread the word on Twitter, Facebook and Instagram. We want to share these ideas with as many people as possible and growing our audience will ensure that Big Biology episodes keep coming.
Art Woods 00:31
And of course, if you want to hear a particular guest or an episode on your favorite topic, let us know you can get in touch with us on our social media pages or through our website.
Marty Martin 00:39
And now here's the show.
Art Woods 00:48
For the past few weeks, the eyes of the world had been on the COP 26 negotiations in Glasgow. For many this summit is seen as critically important in the fight against climate change and the degradation of natural ecosystems.
Marty Martin 00:59
One promising outcome from a few days ago is the pledge by over 100 world leaders to end and reverse deforestation by 2030.
Art Woods 01:07
COP 26 also comes on the heels of the UN biodiversity conference last month, at which attendees declared that putting biodiversity on a path to recovery is one of the defining challenges of this decade.
Marty Martin 01:18
These ambitious and encouraging declarations contrast with the simple fact that today, more than a million species face extinction.
Art Woods 01:26
Most of the world's ecosystems have been impacted by human influences. Besides deforestation, these changes include conversion of land to agriculture, penetration of roads into formerly wild spaces, introduction of invasive species and just plain old degradation from climate change.
Marty Martin 01:42
Another big deal is the removal of large animals from ecosystems, especially large herbivores and top predators. When these species disappear, there can be cascading effects on the rest of ecosystem.
Art Woods 01:52
Some biologists hope to restore these ecosystems using a process known as rewilding. Rewilding can take many forms, many of which are contentious, but one straightforward and seemingly promising version proposes to reintroduce keystone species, including the large mammals and especially predators.
Marty Martin 02:10
Take the kelp forests off the west coast of North America. Kelp is grazed by sea urchins. But in healthy kelp forests, sea otters hold sea urchin populations down to low levels.
Art Woods 02:19
In the mid 19th century, because of their valuable fur, sea otters were hunted nearly to extinction in many parts of the Northern Pacific. Without the top down control they provided, urchin populations exploded and often overwhelmed available food sources which destroyed the kelp.
Marty Martin 02:33
Sea otter numbers have rebounded fairly well in the 20th century. And where the otters have come back healthier kelp forests have tended to follow.
Art Woods 02:40
Potential argument for rewilding, right?
Marty Martin 02:42
Well, before we run out and start trying to engineer natural communities ourselves, there's some important fundamental questions to answer. What are the basic processes that sustain biodiversity and ecosystem function in intact ecosystems?
Art Woods 02:55
And how do we even know whether an ecosystem is intact? Our guest today, Tony Sinclair argues that we need a baseline from which to work.
Tony Sinclair 03:02
Rewilding basically involves two things. Set up, reconstruct the whole trophic cascade, which we then use as a control, this is standard scientific practice, we use that as a control we call them baselines, against which you then use your own particular idiosyncratic type of rewilding and see whether that is stable or not in comparison.
Marty Martin 03:28
Tony is a professor emeritus of Zoology at the University of British Columbia. He wants to know what regulates the population sizes of large mammals and how those populations interact with other local species.
Art Woods 03:38
And as any fan of wildlife documentaries knows, one of the best places to find lots of large mammals is the Serengeti.
Marty Martin 03:45
The Serengeti is located in northwestern Tanzania next to Lake Victoria, but it's famous for its high species diversity, unique geography, and of course huge populations of large mammals.
Art Woods 03:56
Like 1.3 million wildebeest in some years.
Marty Martin 03:59
Since the 1960s, Tony has been studying the bottom up processes that affect wildebeest and other wildlife populations. These large herbivores are simply too big for most predators to take on, so what limits their population size is competition for food during dry season.
Art Woods 04:12
By contrast, smaller bodied herbivores,
Marty Martin 04:15
Think gazelles and dik diks,
Art Woods 04:16
Are regulated by top down processes like predation. Because these little ungulates are small and tasty, they are hunted and killed by upwards of 10 different Serengeti predators.
Marty Martin 04:26
In other words, small herbivores typically have plenty to eat. It's just super dangerous to be out there eating it.
Art Woods 04:31
In this conversation. We talk with Tony about how large mammal populations in general are regulated by bottom up and top down processes, what makes the Serengeti ecosystem so special and how human activity is affecting even this relatively undisturbed place.
Marty Martin 04:44
I'm Marty Martin.
Art Woods 04:45
And I'm Art Woods .
Marty Martin 04:46
And this is Big Biology.
Art Woods 04:47
Tony, thanks for joining us on the show. It's great to have you on. We thought it might be nice to get into the talk just by having you tell us when and how you first got to the Serengeti. I understand you've been working there for a long time and started in the 60s. So tell us about those very early experiences and what you saw and what you did.
Tony Sinclair 05:19
Well, I think, to start with, I should explain that I was raised in East Africa. Zambia, Tanzania, Malawi, and then Kenya. And in that time, as a as a boy growing up, I'd gone to different protected areas, national parks. And so I was therefore a little bit experienced in what was out there and what East Africa was. And then when I went to university, to Oxford, I had already set my mind on wanting to make my career studying African animals. It was something in my blood from a very early age. And I heard that there was a professor, this was day two of my freshman year, who had a project in Serengeti. I'd heard of Serengeti, but I knew nothing about it because it was in a different country. I went to him and announced to him that that's what I was going to do. And he was so taken aback by this forward, young, freshman, that he simply said, oh, well, then you better come with me next year.
Art Woods 06:28
You talked yourself into a job on day two, huh.
Tony Sinclair 06:30
I thought he was just dispensing of me to get me out of his office. But I kept reminding him every few months. And so that's how it came about. We went to Serengeti as my second year undergraduate, he put me in charge of the project that they had there while he went on to supervise, he had graduate students in various places, and left me to it. The very first few days I was there, I was taken out by some one of the technicians to read the rain gauges, they had a number of rain gauges around this area, it's quite a large area, it's 25,000 square kilometers in all, and it took three days to drive around and measure all the rain gauges. And so in that time, I was able to see just about everything. And I was frankly, blown away. The number of animals, the views, the vistas, the diversity of everything, the large mammals, of the birds, the insects, were several orders of magnitude more than anything I had seen before. And it struck me there and then in those first few days that this was so extraordinary, I had to find out why. What determined this place to be so different from anywhere else that I was aware of? And basically, that's what set me on course. I did that project, but in the process of doing that project, the other scientists who were there, there were three other scientists who were there, at that time, came to me and asked me if I would come back and start to study the reason why these major populations of buffalo and others were increasing, because that was what they had discovered from the early count. And so that's how I got involved in it. Just simply because I realized this was unique. Now I say unique, because every place is unique, but this was specially different. This was uniquely unique. So the I mean, let's let's set the stage. Everybody, most everybody I imagine, has seen the documentaries with amazing video of the Serengeti. But can you set us up to know the critical parts that we need to know to understand, you know, the substance of your book, regulation, population regulation, how we end up with biodiversity? What are the parts about the Serengeti that are both amazing, you know, in your experiences, but also critical to your story about the science? Well I think there are three major components here that one could put a finger on. One is the large populations, the enormity of these populations, bigger than any other one terrestrial large mammal in the world. The other is the diversity, the number of species that live there, it's not just number of animals, but number of species. And the third thing is the geography because that actually explains everything else. And the geography is, is this and I think this is something that most people don't really appreciate the overview of, which is that the eastern side of the Serengeti is determined by the very high crater highlands, which go up to 8000 feet. And they create a rain shadow from the rain that blows in from the Indian Ocean to the east, which means that immediately to the, to the west of those crater highlands, we have semi arid conditions. Then at the other side, on the west, we have Lake Victoria, which is the third largest lake in the world, and is large enough to have its own weather patterns. And that means we have a much higher rainfall than one would expect in that kind of environment. And so what we have is a gradient of rainfall from very dry to very wet. And that's unusual. You don't normally get that in a patch of Savanna territory. And it's because of that gradient that, it drives the migration, that the migration is there because we have a gradient in environment, in climate. There is as a result of that gradient, a large number of different habitats. And that large number of habitats means we have a large number of species in everything. So they all start to hang together because of those three things. And we can talk later about why the populations are so large, that's to do with migration.
Marty Martin 11:33
Right, I think that that's definitely something that we want to get to. But this is the downside of trying to do a podcast, trying to talk about something so amazing, and all of this heterogeneity that exists across the landscape, both spatial and temporal, as we'll get to later, but just some interesting anecdotes, let's talk a little bit about Lake Victoria. I mean, this is tangential for sure, but you said that it's the third largest in the world, it's something like 65,000 square kilometers, if that those numbers mean things. But at its deepest point, it's only 65 meters.
Tony Sinclair 12:08
That's correct.
Marty Martin 12:09
That's amazing.
Tony Sinclair 12:11
It's in fact one huge puddle. And it's because it's been dammed up between two rift walls, the East African Rift, that the rift is where East Africa is splitting away from the rest of Africa in a few million years time Africa will be split into two.
Art Woods 12:30
And you expect Lake Victoria to grow during that time, it's going to be part of that rift growth?
Tony Sinclair 12:35
Well, Lake Victoria is just simply an impoundment. It was part of the Congo River drainage into the Atlantic Ocean. But it got cut off by the Western rift. The rift becomes a barrier. And the drainage then turned northwards and became the Nile. But that, prior to, that's several million years ago, back in, you know, 10, 14 million years ago, this happened in the Miocene. But the other side, there was a second rift on the east, which is where the crater highlands are, and that's why there are volcanoes there. And so it becomes impounded, I think, what happened because it's so shallow due to this impoundment, that the lake actually comes and goes, we don't see it on our timescale. But we know that during the ice ages, more than 10,000 years ago, Lake Victoria didn't exist, it was dry. And then it started to refill again 12,000 years ago, and then reached a high point 6000 years ago, where it was 100 meters, 300 feet or so higher than it currently is, which meant that a large part of the Serengeti, Western Serengeti was flooded at that time. And that means that we almost certainly had a different migration at that, in those days. So these comings and goings of the lake most certainly do influence the structure of the Serengeti system.
Marty Martin 14:11
And other piece I want to make sure that we touch on that involves water, but coming from a different place, is you know, you spent a lot of time about precipitation. So my vision, my naive vision, before I learned more about the Serengeti was that it was you know, this gigantic grassland. But as you've just laid out, and as we'll get into in a lot of detail, that's absolutely not the case. But it's also by no means static. You talked about, like the coming and going over years, but even within years, there's major differences in precipitation, right? And not just some times of the year it's wet and sometimes not. In Serengeti, there's multiple different periods when the rains are coming and going.
Art Woods 14:11
Indeed, different periods even within the year, as well as between years. And within the year, we have a dry season, a major dry season, July to October time, and a major wet season, which is sort of March to June time. But there are also shorter periods. And this is due entirely to an interesting phenomenon to do with the sun. The sun travels back and forth across the equator. And as it does, so the rain follows it. Because the sun heats up the Earth, the Earth produces these up currents, and they form into rain clouds. And so because the sun goes back and forth, we have two sets of seasons, two wet seasons and two dry seasons. Because we're right on the equator, we're two degrees, one degree off the equator. And so that's what makes it unusual in having a variety of weather systems. That's really interesting. I was just, in my introductory biology class, teaching about Earth's major climate patterns, and talking about Hadley cells and, you know, heavy rain along the equator, because of this effect you were just describing, but I hadn't thought of it in terms of like, you know, if you're really close to the equator, then you get two wet and two dry seasons, that's quite interesting. I'm gonna, I'm gonna say this to my class.
Tony Sinclair 16:15
Each time it goes by as it goes from north to south, we get one rain following, six weeks, it's six weeks behind the sun, and then it goes back south to north again, and the rain follows again. So that process is called the intertropical convergence zone, where the the winds converge and create the rain.
Art Woods 16:46
But let's turn now and talk about one of the major ideas and major premises of your book. And that's this idea of population regulation. And you pose that as sort of one of the major principles that one needs to understand to grasp why the populations are so large sometimes and why they have the stability or the instability that they do. I think there's sort of multiple ways to get into this, and we want to talk eventually about bottom up and top down regulation, but maybe let's start just by talking about rinderpest. So you made some major discoveries based around, rebounding from rinderpest. So what is rinderpest? And what did it do to the Serengeti?
Tony Sinclair 17:30
Yes, to put it into perspective, let's let's just see what this disease is. It was a major disturbance to the system. It's a virus. It's actually very closely related to measles, human measles. And in fact, there is some suggestion that measles actually evolved from rinderpest. Rinderpest is an endemic disease of cattle in Asia, and almost certainly jumped into man, you know, these days, it's now commonly understood that diseases jump. It's quite possible that what happened is when people lived in the same house as their cattle, you know, cattle below and they lived above, in the loft, that that disease jumped from rinderpest, from cattle into humans, and became measles. Anyway, it's a virus. And it got into Africa when Italians invaded Ethiopia, in 1890, 1889, and brought with them infected cattle from Egypt. And that was the first time rinderpest hit Africa as far as we know. So that meant all of the populations were susceptible. That meant that 95% of the cattle in Africa died, it spread right across West Africa, and all the way down to the cape. And at the same time, it knocked out populations of species that were closely related to cattle, obviously buffalo are, and it turns out, wildebeest are as well. Not all of them, not all of the ungulates are related, closely related, and not all of them get this disease. But it is very much a disease of what we call ruminants, those that chew the cud. It hit in 1890, took six years to get to the Cape of Good Hope, and decimated not only those populations, but of course, the human population, because humans starved. And it was, it really ranks as one of the great pandemics of history. It stayed around after that, basically going in waves for every few decades, up until the end of the Second World War, which time then colonial administrators decided they had to do something about this disease because it was killing off the cattle and disturbing the whole animal husbandry business of Africa. So in 1950 or so they decided that that was the single most important biological thing to study. And that's how research in East African wildlife got started, purely because of rinderpest. After a while, they came to understand what rinderpest was, and they invented a vaccination program, which they started in the late 50s, and vaccinated all of the cattle, it took them a few years to do this. They wanted to, at the same time, eradicate wildlife because they saw that wildlife were the groups that were infecting cattle, and therefore it would be good idea to get rid of those. But when it came to Serengeti, they realized that could not get rid of Serengeti, it was too big an issue, and by then conservation had become, was beginning to become important. It was still in its infancy at the time. But anyway, they decided,
Art Woods 20:59
Are you are you saying that the one of the original ideas was to wipe out all of the the ungulates in the Serengeti?
Tony Sinclair 21:05
It had indeed been mooted that in the late 1940s.
Art Woods 21:09
Wow.
Tony Sinclair 21:10
But by then a certain people put their hands up and said, no, you can't do that. Yeah. So they proceeded with this, under the belief that it was wildlife infecting them. And to their surprise, once they had completed that ring of inoculated cattle around the Serengeti, in the early 1960s, extraordinary thing happened, it died out of the wildlife. And it was then that they understood, or, actually, it was the work that I I did at that time, to show the veterinarians that they got the story upside down, and that it was the cattle infecting the wildlife who were not adapted to this. It was not their disease, it was a cattle disease, and once they were protected from it, it died out of the wildlife. And it died out incredibly fast, like over a year.
Art Woods 22:09
Yeah, it's astonishing to me that, you know, it could have such extensive effects on wildlife and yet disappear so rapidly and so thoroughly, right? And I mean, rinderpest is eradicated now, right? It's extinct.
Tony Sinclair 22:19
Exactly. Yes.
Art Woods 22:20
And that, to me is just sort of amazing for something that can can infect such a wide variety of wild animals.
Tony Sinclair 22:26
Yeah, it's, but those wild species did not, had not evolved carriers, where certain individuals can, if you like, co-habit with this, that hadn't happened. So you either got it and died or you recovered. So I think that was the reason. But it happened in two species, buffalo, and wildebeests, one year apart, the data show, and remarkably fast. And it was a bit of luck how we found that, and I finally reached that conclusion in 1970. And I was able to then tell the vets, actually, this is the real story.
Marty Martin 23:06
So you're, then I want to circle back to frame this in the context of regulation, because you mentioned just a minute ago that you were recruited to work in Serengeti to figure out why the populations were getting so big, or were so big, and yet to hear everything we've been talking about, at least for a few species, that at some point, they were small, but the connotation of regulation, obviously, is something about hovering around a point or coming back to some equilibrium. So can you connect those dots for us?
Tony Sinclair 23:35
Okay, so really what this is getting at is the first question had been why the increasing? And I've got to the answer to that, which was the disappearance of this disease. The second question was, what's going to stop them increasing? And so that is where this concept of regulation comes in. The underlying idea, and I'm not sure if this, you'd like me to just sort of give you a precis of the idea at this point.
Marty Martin 24:04
Yeah, I think it'd be great.
Tony Sinclair 24:05
All right. So it's really quite simple. Populations have inputs through births, and they have outputs through deaths. And if the births equal the deaths, then the population doesn't change in number. So what regulation does is when there is a lot of food, then there's high reproduction. Females are in good condition and reproduction is high and survival of the babies is high. And at the same time, deaths are low because everybody's getting a lot of food. So usually, under those conditions, you have births greater than deaths. And if you have births greater than death, the the population increases. But as the numbers increase, there is less and less food per individual in the population because they're eating it until at some point, there is not enough food to go around and the deaths go up. And they gradually creep up, in fact, as you see the population increasing, you see the death rate going up, until at some point, the death rate matches the birth rate. And that's when the population stops. And that's what we call regulation, it's exactly the same thing as a thermostat in a house where if you set it, then if you're too high, the thermostat works such that the temperature comes down, and vice versa. And it's exactly how populations work. Now, that was the theory. But the problem was at the time is that nobody had any real data on this. It was a great idea, but they couldn't get it because the nature of the populations was such that it was too difficult, you know, working on insects, for example, you don't really see a dead insect and you let alone know what kills it. And the same for small birds for that matter. How often do you see small birds laying around dead? Not often, compared to how many actually die. But here, all of a sudden, we get huge animals that lie around, and you can find them dead. And you can actually do autopsies and find out what kills them. So I was in a position at that point to actually examine this, because essentially, the whole argument centers around deaths and what causes them. So that's, that's regulation. And by watching, and counting, and counting the births and counting the deaths, I was actually able to see that death rate creeping up higher and higher, until it matched the birth rate.
Marty Martin 26:41
Right. Okay. So we've got regulation, which I think I've got a handle on now. And you spent some time with kind of two flavors, or two different processes by which you got that. You just described regulation coming from bottom up, so maybe let's start there. And tell us about wildebeest in that context. But I want to get to top down regulation, and especially the role of predators, if for no other reason than you're going to tell us how you guys went down the carcasses and had to jump into the car to get away from lions and such. So let's, let's start with the wildebeest, though, how does bottom up regulation work for wildebeest?
Tony Sinclair 27:15
Alright, so again, if we go back and look at the if you think, theoretically, there are two major ways that animals can die, as I say everything centers around deaths, and there are two major ways. One is that they starve, they just don't get enough food. And the other way is that somebody eats them, because in ecology, everybody eats everybody else. So wildebeest could get eaten by predators. In fact, when I started, and I was asking questions like that, my fellow wildlife biologists, and also, you know, national parks managers said, of course, there's enough food, you see all of this grass waving around, there's can't possibly run out of food, so therefore, it had to be predators. That was the rationale at the time. However, I didn't buy that idea, because I understood that in any of these processes, there's such a thing as called a bottleneck, that is a some short period of time in the year when there may not be enough food, even though there's plenty of food for the rest of the year, that bottleneck, that short period of time, is all that you need. That is the critical time. So I set about to look for that. And it was quite clear when that was taking place, and that was in the dry season. And that was when we found all these carcasses lying around. And I had to then find a way of understanding what was killing them. Now we could do a lot of detective work, we could find out from this detective work, what the carcass looks like. This essentially is CSI wildlife. And we could tell whether things had been killed by predators, whether they had died other than predators and being scavenged by predators, or whether they had actually died from something else. And that something else would either be starvation, or disease.
Art Woods 29:04
And can you actually just walk us through that? So if you walk up to a carcass, how can you tell those things?
Tony Sinclair 29:10
Right. So when predators kill an animal, the first thing they do is pull the rumen contents out, because it's full of fermenting grass and predators don't like eating fermenting grass, it's not their diet. So they pull it out and drag it to one side. And so whenever you find a carcass with the, with the rumen contents pulled to one side, you know immediately that it's predators. Then what type of predators, well, lions, they kill their prey by strangling them on the neck. So there are always tooth marks, tooth holes in the neck of the animal. If it's hyenas, they always crack open bones, lions never do that, cats never crack bones. So if you've got a cracked bones, you know, it's hyenas. The other thing is that when predators kill an animal, it bleeds. The animal's alive, and, and it therefore bleeds out. If they scavenge an animal, the animal is already dead, it doesn't bleed, so there's no mark no bloodstains on the ground, and there's usually a lot of blood so that blood stain is extremely visible. So no blood means that's not a kill. That's a scavenge. So those are the kinds of clues that you can use, and they seem to be really robust. But the real problem came, how do we tell starvation? And at the beginning, I was at a loss. Nobody had ever asked that question. When I talked to animal husbandry people, they all said, well, that's ridiculous. Of course, we don't have starving animals, we feed them.
Marty Martin 30:52
That's the point.
Tony Sinclair 30:53
That's the point. And nobody else had done any studies of this sort in East Africa, because they'd hardly been any research. Nobody had asked questions of this sort. They just didn't do that kind of thing. And eventually, I did discover it. And it was in a remarkably obscure journal, in New York State Conservationist, I think it was, which I found in a museum of all places. And in that was this little article in 1949, talking about the bone marrow of deer dying in New York State. And I looked at this and I thought, well, maybe that's something we could look at. I did ask around, to see if they knew anything. And they all just poured scorn on it, and said, of course not. That's, that's ridiculous. It's not going to work at all, and anyway, that was, that was American, and that doesn't apply to Africa. Luckily, I did pay no attention to those comments, and decided to take it further and look at animals under different conditions, including what that bone marrow looked like, in animals that were alive. Now we had to kill some animals, we had to take samples. In those days, that was the only way we could do it, it was before immobilizing drugs had had been brought on. So the only way we could actually do anything is to do some autopsies on healthy animals., not only just for that, of course, but we were also looking at the diseases of animals, which the veterinarians, the wildlife veterinarians were interested in anyway, and also the reproduction and so on. And in the process, I was able to then build up a picture of what the, of what a healthy animal looks like when it comes to its fat reserves. So we got that picture, and then I compared it with the picture from what dead animals look like through the year. And it was quite clear that the bone marrow was the most important indicator that they had run out of food. And that occurred in the dry season, as expected. So finally, we got to that point. And in fact, it's such a good indicator that we could just tell by looking at it in the end. I had to, I had to demonstrate that, of course. But by the end, all we needed to do is crack open the bone, look at the bone marrow, and we could tell then, what state of nutrition it was in.
Art Woods 33:29
Fantastic. So you have some really nice data plots and those chapters showing also that as wildebeest population sizes increase, then the greater the percentages of carcasses that have this sort of starvation indication in their bone marrow, right. So that's an indication that there's more food limitation, the larger the population gets, which is in, in a real sense, bottom up regulation.
Tony Sinclair 33:52
That's right. So having actually found starvation, I then had to demonstrate that that was the thing that was responding to the size of the population. In other words, was it increasing as the, and that was what we eventually found. It took many, many years to get that of course, because nothing works very fast. Insects work fast, large mammals work somewhat slower.
Art Woods 34:16
Let's also talk about top down regulation by predators. And maybe this is a sort of two part question. So one is, what is the evidence for top down regulation of different populations, perhaps of different body sizes? And then the second part is, I can imagine there being a lot of interaction between bottom up and top down processes in the sense that when animals are starving, or on their way to starvation, they must be more vulnerable to predation, right? So those things would seem to have to interact at some level.
Tony Sinclair 35:00
Okay. All right, that's a complex question. So I'm going to break it up into two parts. Firstly, I'm going to deal with how predation also interacts with starvation. That makes more logical sense. So things don't just die of starvation, they are losing fat while they're still alive and, and the fat is there as a fat store, it gets them through the worst time of the year, when there's actually not enough food for them to keep going on by itself, they have to rely on these stores. That's what fat is for. That's the evolutionary, necessary adaptation. However, they have to enter that dry season with a sufficient fuel supply. You got to have enough gas in the tank, so to speak, to get you to the endpoint, which is the end of the dry season. If you don't have enough gas in the tank, enough fat on board, then you have to go and supplement it by getting extra food. And that can only be found where most animals don't go, because that's the reason why the food is still there. And they, those most animals don't go because that's where the predators are. And the predators are there because of features of the environment where they can more easily capture prey. So low fat supplies force animals into risky environments. And therefore, predators say thank you very much. And they catch some. Predation can actually, if you like, speed up the process of starvation. And so that is how the two interact. And in fact, predation alters the behavior of the prey by forcing them into areas where predators can't be, but they then eat up all the food, and then they have to go into areas where predators can catch them. Okay, that's the first part. The second part is pure top down regulation. Predators have to be able to impose a mortality, a death rate, in such a way that it matches the birth rate of those particular prey. What we found, initially, our attention was drawn to the fact that when we tried to find dead animals in most of these other prey, now, I should now mention some of these species. There are a whole range of small prey much smaller than the wildebeest, that we never found dead. Now that the reason is the same as why you don't find dead birds and so on is because things eat them up so fast that they never leave the carcasses. So we had to find them quickly. And we did that by putting radio collars on them. And those radio collars were designed so that they told us when the animal was dead. And all we did was monitor, and then when we heard the right signal, we went out and look for them as fast as we could, and generally, we were able to get enough clues to see what was happening. And without exception, all of these small guys, the small species died from predation. So that drew our attention to the fact that although the large species we'd been watching initially, buffalo and wildebeest were regulated by food, clearly, this was not happening with the other species. So we looked at a range of different species, and the pattern fell out. Little species died of predation, and above a certain threshold, sorry, body size of about 150 kilograms, then it switched, it was a sharp switch from predator regulation to food regulation. And in fact, it has to be that way, you can't have both, you cannot have two processes regulating simultaneously. Mathematically, that doesn't work. So you actually do have to have a switch. And indeed, we actually saw that switch, from one body size to the next body size.
Art Woods 39:18
So it seems like one application is that if species evolve large enough body size, then they can, in some sense, escape the high pressure from predators, and then they're more likely then to become bottom up or food food limited, right. And I think that's one of the points you make in the book is that the Serengeti is special in part because it still retains so many species and so many individuals of these very large bodied herbivores that are subject to bottom up regulation. So and if we just broaden the view for a moment, why wouldn't this also have been the case in many other ecosystems historically, and is that you know, we've lost a lot of those those big bodied herbivores that would have been subjected to that kind of bottom up regulation, right?
Tony Sinclair 40:03
Yes, you're quite right. In fact, most areas of the world had at one time or another, going back many 1000s of years now, but had large populations of very large animals of the elephant size, rhino size, bison size animals. And they, from what we understand in the archaeology, were sufficiently numerous. Some of them showed migration patterns. And they behaved in much the same way as what we're looking at in Serengeti, which really points to the Serengeti being a rather abnormal holdover of the Pleistocene, you know, something that was a million years ago. But Europe had a lot of these North America, of course, had a lot of these mammoths and woolly rhinos and giant bison, Australia had them, New Zealand had giant birds, all of them had giant animals. And so and as, as you say, they have outgrown their predators, there have been larger predators, especially at that time. But even so, they got too large for predators to be able to keep them down. Now, there's something that I haven't actually mentioned yet in this discussion and I think I should bring this in. It's not just a single predator that keeps a prey species down. The whole point of what we found was that it is the combination of predators that is able to keep a prey species down, that is, regulate it through predation. So if you look at the number of predators, the number of predators species, that feed on prey of different size, what you see is that very large prey like buffalo have a single predator, lion, nothing else can even attempt to kill a buffalo. But once you get down to say, wildebeest, then there's 2, 3, 4, predators, leopard lion hyena, and you get down to the tiny ones, there's something like, the tiny prey, I'll mention a few names. Dik dik is one that maybe people would be familiar with if they went out there, those ones are 10, 20 kilograms. They have as many as seven different predator species eating them, well, it all adds up. If you have that much, there's basically everyone gets killed, every prey individual gets killed, if you got that number of predators around eating you. So one predator misses another predator get you. So it's the combination of predators that matters here. It's not just a single one. So that's where it requires the whole combination, the whole community for this pattern to evolve.
Marty Martin 43:03
So, Tony, I mean, you sort of intimated what might be going on a couple of different times, but I'm just going to ask the question directly. What's regulating the predator populations? Is it all bottom up? Or can, you know I think a lot about infections and parasites as you do, should, can we think about those as top down control, and do we have evidence in Serengeti?
Tony Sinclair 43:24
This is actually one of the most interesting aspects which actually biologists are still having to, to think about. At the moment, I think the evidence points to disease working, what we say, synergistically, that means hand in hand with undernutrition, not getting enough food. When that happens in any species, the prey or predator, then the immune system is compromised. And then diseases take over. And usually every species has a large number of parasites, microparasites, viruses, bacteria, and so on, and macroparasites. And any one of those can take over, it's it seems to be a lottery, just whoever is, you know, in the right place at the right time, takes over and then can kill the individual. So that applies to lions just as much as it does to a wildebeest. Obviously, predators must, for the most part, be bottom up. However, there's some indicator that it's possible that a disease might be sufficiently effective to keep a predator population down. Now, this is contentious. I don't think we have a very clear signal on that. I mean, some of our modelers have looked at how rinderpest drove the whole system at one time. And so from that point of view, it was actually a top down driven system determined by a disease. But that was an artifact, and it was an artifact of because the animals were not evolved to withstand it. So we can't really look at that and say, yes, that's the natural order of things. It may or may not be an aberrant situation. So at this point, I think the jury's still out on whether diseases can actually operate as a controlling factor, that is, a regulatory factor other than, instead of just killing off animals that are going to die anyway, but just speed up, speed up the whole process.
Marty Martin 45:41
Right. I know that Pete Hudson, I mean, had some classic studies on the effect of some kind of worm on I think red grouse in the UK. So there's evidence of top down regulation via parasites, but it's not, it's definitely not Serengeti, and it's definitely not predators in the sense that we're thinking lions and hyenas. So, yeah, are those are data, those data, you're hinting at that too, those are not easy data to come by. I mean, predators, by definition, are rarer than other things, so statistically, that becomes a problem. But you can't just walk up to a lion and ask what what infects it? That's a very tricky thing to do.
Art Woods 46:21
Tony, in your book, you developed a number of other principles, in addition to, you know, top down bottom up regulation, at sort of higher ecological levels, so things about, questions about how do you get so much biodiversity in such a small space? And what sorts of complex interactions do you have among the components of an ecosystem? I think in the interest of time, we can't step through those in any detail, because we want to get onto a couple of other things that you talk about at the at the end of the book, except I want to be self indulgent, and ask about one thing that's of particular interest to me. And that's this story that you tell about the dung beetles. So I myself am an insect person. And I love dung beetles.
Tony Sinclair 47:05
I thought you were going to ask about that. I said Art is going to ask me about dung beetles.
Art Woods 47:12
They play a really interesting role in supporting grasslands in parts of the Serengeti. So tell tell us about how they do that?
Tony Sinclair 47:18
Well, for a start, I'm really intrigued that insects can play such a driving role in the system. I mean,
Art Woods 47:25
I have to say, I'm not surprised, but, you know.
Tony Sinclair 47:28
Well, I was delighted at this. And of course, also the role of grasshoppers too, which I studied a long time ago. But for the dung beetles, it became clear that especially when, as a start, we were looking at dung, because dung had the hormones, and we could we were looking at that to tell whether females were pregnant or not. This was a new way of getting at the pregnancy rate without having to do anything drastic. And so we had to watch and this involved watching females poop. And when you watch anybody poop, they don't do it. So we spent hours. But then there's 10,000 of them in front of you, and one of them does, and then you race over, and there's 10,000 other heaps there. So it took quite a bit of training to find the right one. But in the meantime, we discovered the dung beetles that got there before us. Like 15 seconds it takes for them to, to come in, and within three minutes, the dung is gone. They rolled it all up and buried it. So that really brought it home to me that here was a process going on with insects that was vastly quicker than anything we'd anticipated. But we'd also notice that we only saw this happening out on the plains. And of course, the wildebeest are on the plains in the wet season. So in the wet season, we saw that this process of dung, dung beetles, and recycling into the soil. And we know, we haven't talked about migration yet, but we know that the driver for migration onto the plains is the very high nutritious grasses on the plains, the highest in the whole ecosystem. And one of the reasons that they are high is because dung beetles are recycling that nitrogen so fast, it's not taking years for it to seep down and, and so on. It's taking a matter of a few days or a few weeks to recycle that nitrogen. At the same time, conversely, we noticed that there were no such dung beetle activity and no dung beetles in the dry season. The ground is hard and they can't operate. They can't dig into that ground. So they just aestivate, they stop operating. So we have dung beetles affecting one part of the park and effectively zero effect in the other part of the park. And I realized then that was tied in with the migration and it's almost certainly one of the drivers for the migration.
Marty Martin 50:04
Yeah, the role of the dung beetles in causing the nitrogen cycling because of the precipitation, which then is influencing the movement of huge numbers of animals. How's that Art, are you happy about the role of your dung beetles?
Art Woods 50:18
I am. I mean, I feel like we should maybe spend a few minutes on migration just given the central place that it plays in the book. So, you know, without spending too much time, Tony, do you want to tell us just what are the major patterns of migration and why?
Tony Sinclair 50:31
Well, of course Serengeti is now famous for the fact that we have this huge population 1.3 million wildebeest, and these wildebeest go onto the plains in the wet season, to get the, the very high nutritious grass, short grass, which they like most of all, they like grass, which is five to 10 centimeters tall. But all animals need water. That's, if you'd like, the primary driver. So the plains have no stored water and no rivers, and therefore, when the dry season comes along, they have to leave. So they go to where the water is, which is in the rivers in the savanna area, in the dry season, where the grasses are poorer. So that's really, the rain drives them off the plains, and the nutrition drives them onto the plains. So that's how it works. Now, the question is, why are there so many of these animals, and it turns out that all migratory species have large populations because they can access this one feature, which is common to all migrants, of temporary high value food supplies. Now, that applies to birds flying to the Arctic, applies to whales going up to the Arctic, and it applies to wildebeest, and every other form of migration, obey that rule. They have, therefore, access to greater food supplies than animals that don't migrate. You don't have animals that live on the plains not not much anyway. They have to live where the water is, so they're stationary. And they have to put up with what resources they have at that time. So they miss out on these temporary food supplies, so their populations are less. So that explains why we have such large populations. But then that begs the question, well, why wildebeest and why not buffalo? And there are two reasons. One is it has to be the right kind of food. So birds fly to the Arctic, in order to eat insects. Seed eaters do not do that, because that food supply doesn't behave like that. So only those that can eat insects fly to the Arctic, only wildebeest, that eat short grass, can go to the plains, Buffalo can't do that because they don't eat that grass. It's not their type of food. The other adaptation is you got to actually be able to do that, you have to be able to move like that. Wildebeest are adapted to long distance movement, buffalo are not. So both of those things have evolved in order to take advantage of the temporary high value food. And that's what migration is all about.
Marty Martin 53:25
There's been a lot of attention, we want to move to another topic. But you know, again, migration is so prominent in Serengeti, we need to devote some time to it. There's been a lot of speculation and research in other migratory systems about moving away from danger, and especially moving away, I'm gonna go back to parasites. Is there any evidence or any effort right now to ask about the role of disease in the movement of wildebeest, or zebra, are any evidence at all?
Tony Sinclair 53:52
I think at this point, we don't have evidence of them doing that, we'd have to get a picture of the distribution of the diseases, if you like, through, you know, parasite loads in the dung, for example. I think biologists are working on that at this point. But I haven't seen any particular results on it yet. However, I do suspect that that may actually be something that takes place on a smaller scale amongst the, what we call the residents, the non migratory species. All of them move in the season, they don't just stay in the same place the whole year round. Everything moves, but they just move on a much smaller scale. And there may well be a relationship between the parasite load in the dung and where they are. However, as I say, at this point, we don't know much about it. And I can't give you a clear answer.
Marty Martin 54:56
Yeah, fair, fair. So yeah, Tony, we're sensitive to your time and we have so much more we want to talk about. So if you can stick with us for maybe three or four more questions, when I say that question, you know, these are these are not simple yes and nos. So you can take them as you will. But all of them are sort of, almost all of them are falling into the human impacts on the Serengeti and the sort of, because humans are influencing the system so much, how should we think about it? How might we manage it? How might we mitigate human impacts? Can we get there by you telling us about, sort of explaining how poaching makes sense of the sort of difference in the amount, the number of elephants in the Mara in Kenya, versus in the Serengeti, because that's a really convoluted and yet very cool story that gets us into sort of unexpected impacts of human activities.
Tony Sinclair 55:49
Yes. Okay, there are differences between the two countries. So just to start, Serengeti spills over between two countries, most of it is in Tanzania. But a portion of it, a small portion of it, is in Kenya in what is called the Maasai Mara reserve. So therefore, there are two administrations that affect the conservation. Well, there are several but there are two national administrations. There was a unfortunately a period of very severe poaching back in the 1970s, and 1980s where, in Tanzania, where 80% of the elephants were removed from the Serengeti for ivory. Due to socioeconomic and political reasons, Tanzania was unable to control these poachers. On the Kenya side, the Kenyans were much more capable of controlling the poachers, and the population of elephants did not decline. In fact, it increased slightly because some of the elephants in Tanzania moved up into Kenya. And what that meant was that the density of elephants and the effect of elephants on the vegetation in Kenya became different from that in the Serengeti during those two decades. And that made a huge difference in the habitat structure of the two areas, and it was only by piecing together that story that we were able to explain why we saw one set of dynamics in the vegetation, and we haven't talked about the dynamics of vegetation, but there was one one sort of dynamics in Serengeti, and yet a completely different sort of dynamics in the Mara.
Marty Martin 57:40
Do you want to say something more about those dynamics? I feel like we're perfectly set up for that.
Tony Sinclair 57:43
Right. So having introduced it, I better say something. So what was happening in the Serengeti, for the first half of that last century, was severe burning. It was to do with trying to get rid of tsetse flies, which spread sleeping sickness and other disease. And so there was a policy of burning the savanna in order to get rid of this insect, another insect, Art, that was driving the system. And this severe burning, obviously killed off a lot of baby trees, of seedling trees. And eventually, after many decades, 50 years or so, we eventually had a situation where all we had was large trees, which were out of reach of the fires, and a grassland. It was what one would call a parkland, it was rather pretty, and in fact, a lot of people when conservation really got going in the 50s, that's what they thought Africa really looked like. In fact, it was an artifact, it was completely wrong. It was an unstable age distribution of the trees. And then of course, all the old trees died off all at once. And immediately, we had these trees turning into this savanna, turning into a grassland because of the fires. And then the wildebeest population started increasing, and they, they went from 200,000 to 1.3 million within the space of 15 years. And in that time, as we talked about, they ate up all the grass, they ran out of food. Well, there was no grass there for the fires to burn and the fires stop burning. And because the fire stopped burning baby trees were able to grow. And all of a sudden, within a very few years, we had a mass of baby trees growing up, which has now turned into a much more mature savanna 40 years later. And then that caught us by surprise, because when, and I also worked in the Mara park for many years as well, and we knew that the Mara didn't have these trees. It looked all the same, other than the fact that were no trees when they were all coming back in Serengeti, and yet we knew from historical photographs, and this is where history was important, that the Mara was in fact a dense savanna back in the 1940s. So why, if trees can grow there, as we now had the proof, why did they not come back like they did in the Serengeti? And I set a student on onto this, Holly Dublin. And she did some detailed studies of the survivorship of baby trees, and watched elephants, and came and realized then that elephants were completely capable of pulling up all the baby trees. They were so good at it, that they could keep a grassland as a grassland, and prevent the trees from coming back.
Art Woods 1:00:41
Even with no burning.
Tony Sinclair 1:00:42
Yes, they both had no burning. But in one case, trees were able to grow because the poachers had removed the elephants, and in the other case, the trees could not grow, because the elephants are still there, and pulling them up. And that explained why we had this two different states as we call them, where we have trees and no trees, and both have elephants.
Art Woods 1:01:04
What's what's happened to elephants in the Serengeti? So poaching came under control after the 80s, right, and so elephants have been increasing in the Serengeti. So do you see dynamics in the Serengeti now that are much more like they were in the Mara?
Tony Sinclair 1:01:20
At this point, it seems elephants are not capable of changing the savanna into grassland, it requires fire to operate. However, elephants are capable of thinning it out. But I don't think they're capable of removing all of the trees. So they, that's why there are two states. Elephants can hold it in one state, but they can't get it into that state, it requires another factor to get it there, and that's where fire comes in. But once fire did that trick, then elephants can hold it there. So it's an interaction of wildebeest, fire and elephant combined, that, very nice interaction, that explains this two state system.
Art Woods 1:02:14
Great, well, I think maybe at this point, let's switch over to one of your later chapters and talk about rewilding, which you spend quite a bit of time on in the book. And you do a really interesting approach to this idea by talking about the ecological principles that you've developed earlier in the book, and then talk about how violations of those principles in different places can lead to degradation of ecosystems, and that then rewilding involves reestablishing one or more of those violated principles. So maybe let's just start if you can just say what is rewilding? And how do you think about that in terms of the Serengeti and other degraded ecosystems?
Tony Sinclair 1:02:54
Well I should preface this by saying just about everybody under the sun has their own view and idea and dogma about what rewilding is.
Art Woods 1:03:03
Yes, yes, there's a lot of that.
Tony Sinclair 1:03:05
And that was what really got me thinking about surely can we not make logical sense of this? So we'll start at the beginning, which is, we understand from the Serengeti that what you've got to have for a system to work properly, that is, it is stable, and capable of withstanding disturbances. We have a word for that called resilience. In order for that to happen, you've got to have the whole set of trophic levels, that is the levels such as predators, herbivores, plants, minerals, that's what we call the trophic cascade. And that's essentially what you need to have. If you disturb that, then things start to go wrong. So rewilding, therefore, logically means that what we're trying to do is get that natural trophic cascade back to where it was, with the species that would have been in place if we had not removed them, if humans had not disturbed it, and removed those species. So that's essentially what the logic of rewilding is about. Now, when you put it in those terms, it means that you're trying to get back to some complete community of species. The problem we have, of course, is that everybody's ideas about what they want in nature does, usually does not involve that. It usually involves just a portion of that, just one thing or another. I'm not going to go into all the details, but because they are, if you like, idiosyncratic, that it means each one has a preference for one particular bit of the ecosystem, one bit of the trophic cascade, we have actually no idea whether those things are stable or not because they're not the full set of species. And the only way you can find out if they are stable, is comparing your particular set of preferences with an area that has the complete set. And so rewilding basically involves two things, set up, reconstruct the whole trophic cascade, which we then use as a control, this is standard scientific practice, we use that as a control, we call them baselines, against which you then use your own particular idiosyncratic type of rewilding, and see whether that is stable or not, in comparison. So that's basically the logic of what we're talking about. So you don't just accept on face value that what we want to do, for example, is simply ecosystem services. Because that's only a subset of all other, all of the processes in an ecosystem, and if you only focus on one, what about all the others, and if we don't have the others, almost certainly that system won't be viable, it will collapse. So that's what we're getting at here is get down to some objective of getting back to a complete trophic cascade. And that's what we found in the Serengeti system. Tony, when you're talking about complete, I would imagine that, this is not my area, but I can imagine that people would get hung up on complete, depending on the biases that we have, you know, we're plant people or we're large carnivore specialists, or, I mean, especially the thing I'd like to hear you you respond to is this disease world. And you know, it's all the rage in biology now to talk about the microbiome. At what point is it fair to call things complete? At what point like, would we make everybody happy? And would we have a defensible biological position of completeness? I would imagine that, and I can't say I know, but I would imagine that the normal endemic diseases of an ecosystem would actually be present once you have brought back the other species. It's possible that they may not be, but almost, I would say that, probably, you would get that. For example, you have a huge set of microbes in the soil. And those microbes where they've studied them do come back once you start bringing in the right ungulates. So there's a lot of self reintroduction that takes place once you can get some of the basic components there. So I wouldn't be too worried about having to physically reintroduce every single microorganism in the world, if you like, to a place. I think you do what you can, and likely get back to something that might be similar to what you had before. But having said that, remember I'm saying you've got to compare it with a baseline. So you actually know you are, at least theoretically, in a position to find out whether you are missing something, including diseases, compared to the baseline. So that's the whole point of the baseline, is to tell you whether you're missing out on something, even if it's not obvious.
Marty Martin 1:08:13
Right. I think that was the part, so like you said, there's a lot of different perspectives on rewilding, and I'll just say again, that this is not really my area, but one of the parts of this section of your book that was appealing to me is that you set it up with these steady states. You know, you introduced the idea of population regulation, and we've talked about the thermostat and homeostasis, and, boy, Art and I talk about that a ton between each other, and then on the show as well. But in the context of baseline, I think you're not just saying that there's some sort of point in the past, this idyllic condition of the Serengeti, that is in some romanticized, you know, romanticized version of it in your head, you're actually talking about an ecologically justified baseline in the context of a steady state, right, there's a, there's some point that these communities will move towards, and we can trust that the integrity is maintained. And that's the baseline to which we track them, not some, you know, Lion King version of Serengeti.
Tony Sinclair 1:09:12
I do want to emphasize, though, that we are not talking about some kind of stationarity here. One of the things that I emphasize in the book is how everything changes all the time. Now, I'm not talking about disturbance. disturbance is a different concept to change. What we have in the world is that our ecosystems change all the time. And that will take place whether or not we've got anthropogenic climate change. So just as an aside here, it's no good trying to stop climate change. It's going to happen anyway. So what you have to do is plan for it. Now in our baselines, we recognize those baselines will be changing over time. We do not want to go back to some point in prehistory, or some point in history. We want to go, what we're saying is what would the undisturbed system look like now, that would have changed from sometime in the past? So we're only looking at the present. We're not looking at anything way back. I mean, that's one of the great hang ups for rewilding was they want to go back to some point in history. No, we can't do that we should not be doing that, and that's not the objective. And at the same time, everything changes all the time. So what does that say about regulation? It says that, because we haven't talked about this word equilibrium, but equilibrium is the point at which births and deaths equal. Well, that is a changing baseline, that can change with the environment. So we've got a shifting baseline all the time. And our disturbed system is shifting as well. But it's shifting for two reasons. One is because of the environment shifting, and the other is because of human impacts. So what the baseline does is exclude the human impact, but leave in the environmental change.
Art Woods 1:11:11
So, if we had to make this more concrete for, say, a degraded ecosystem, so we've got the Serengeti as sort of a, you know, a baseline system for understanding what a healthy ecosystem looks like, if you had to advise a group that was going to try to rewild a degraded ecosystem, what's the practical advice that you give them about how to do that?
Tony Sinclair 1:11:31
Well, let's say if we take Serengeti to start with, we have this remarkable juxtaposition of agriculture, and a hard boundary to the national parks, literally changes within a few meters. In agriculture, all of the native trees have been removed every single one, the grasslands have been changed from native species to monocultures of exotic species, the the, if you like the hedgerows, are all introduced. So we have a major disturbance, basically, the whole thing. 80% of the birds disappear, 50% of the insects disappear. So we've got a major disturbance. So how do you bring that back? Well, they have got, for example, in agriculture, woodlots, which they grow, in Africa, they grow Australian eucalyptus trees, and and Australian acacia trees. Well, no insect in Africa goes and eats those things, because they're not adapted to eat those things. What you need to do is start bringing back portions of the system, particularly in the plants. So you can have coppices, you can start growing native trees instead of exotic trees, you can have coppices of vegetation, you can start building hedgerows out of native species. Once you start building up the plant base, then other things start to come back on their own accord. So that's the first practical thing. Now we recognize that in many cases, you cannot get the whole trophic cascade, you cannot get lions in agriculture. All they do is eat cattle, and that was going to annoy the people. They might even eat the people.
Art Woods 1:13:26
If they run out of cattle, then they turn to the people, right?
Tony Sinclair 1:13:29
Oh they do. Absolutely they do. My colleague Craig Packer studied that very closely. And so we recognize that you sometimes can only get part of the trophic cascade. So we have to monitor what goes on in order to see whether, by missing a certain component, we'll get into an unstable situation, or whether we can maintain some sort of resilience in the system. Now, there's a nice example in Scotland, where they did this. They took about, you know, Scotland is heather moors, with no trees on them. And that's a complete artifact of human destruction of several centuries ago, or even 1000s of years ago. So they're bringing back certain valleys, they're gonna regrow them with the vegetation that was there before, and is currently in Norway and Sweden. So they actually have a baseline, they know exactly what that should look like in the present day. And they're replanting those trees in this valley. And lo and behold, all the species of birds that we've never seen for ages are coming back. They are self introducing. So that's the sort of process that we can talk about. So bring in some and then other things start to snowball if you like.
Art Woods 1:14:46
So that sounds like kind of a bottom up approach in the sense of like the trophic cascades, right you start with the plants.
Tony Sinclair 1:14:53
Yeah, you absolutely have to.
Marty Martin 1:14:56
Well, I have one other question, this is a completely different type of thing but just really quickly, Tony, do you think that there are multiple equilibria that we could manage the Serengeti to or is there, how are you thinking about that?
Tony Sinclair 1:15:09
Well, I've only thought about multiple equilibria in a natural context, that is nature can create those things. Now humans, of course, can also do it because humans are predators. They're predators on all aspects of the ecosystem. They're predators on plants, they're predators on the herbivores, and they're predators on the native predators. So each of those steps can create a different state. But we don't know if they're stable. And that's why we need to have a complete system somewhere with which to compare.
Art Woods 1:15:49
Well, Tony, this has been a super fascinating conversation and really enjoyed talking over these various issues and really enjoyed reading your book, and we just wanted to end by just asking you one last question, which is, is there anything else you'd like to say that we haven't talked over that we haven't asked you about? I think you basically covered most of the major issues that I wanted to deal with, I think the main point is that if you don't pay attention to these rules of how systems work, then things go wrong. And that's the same as in physiology. And we have to look on whole systems in that form as some sort of mega body that needs to be maintained in order to get long term stability. And that's the insurance policy for our species. We've got to maintain these ecosystems. If we don't, then I think we, well, there are two issues, one, one is if we don't do that, we're almost certainly going to put ourselves in jeopardy. But the other one is a moral issue. What we have in front of us are wonderful groups of species habitats, and that we have enjoyed, we have an obligation to pass that on to future generations. Not everywhere in the world, this is where a lot of people complain, so you're just trying to stop everything? And the answer is absolutely not. We need to have a portion of every biome that is like that, so that you can't extract and abuse every bit of the world 100%. Humans can't claim that I think that's too greedy. They might take 90%, but there still has to be some percentage, which is left as our baseline, but also as something for future generations. So that's my philosophy. Love it. All right. Well, thanks so much, Tony.
Marty Martin 1:17:49
Thank you very much.
Art Woods 1:17:50
Really enjoyed talking.
Tony Sinclair 1:17:51
Likewise.
Art Woods 1:17:59
Thanks for listening to this episode. If you want to learn more about Sinclair and his work, head over to the Big Biology bookshelf and check out Tony's new book A Place Like No Other: Discovering the Secrets of the Serengeti.
Marty Martin 1:18:10
And if you like what you hear, let us know via Twitter or Facebook or Instagram, or just leave a review on Apple Podcasts. And if you don't like what you hear, well, we'd love to know that too. All feedback is good feedback.
Art Woods 1:18:19
On the next episode, we talk to Arvid Agren about his new book called The Gene's-Eye View of Evolution. In it, Arvid argues that Richard Dawkins's concept of the selfish gene is still one of the best ways to understand evolution and particularly adaptation.
Marty Martin 1:18:34
Thank you to Steve Lane who manages the website and to Ruth Demree for producing the episode.
Art Woods 1:18:37
Thanks also to Kyle Smith for writing the script and Brad van Paridon, Jordan Greer, Natasha Dhamrait, and RB Smith for helping to produce this episode. Keating Shahmehri produced our awesome cover art.
Marty Martin 1:18:47
Thank you to the College of Public Health at the University of South Florida the College of Humanities and Sciences at the University of Montana and the National Science Foundation for support.
Art Woods 1:18:55
Music on the episode is from Podington Bear.