The Life Scientific: Tim Coulson

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1:04Tim Coulson:Hello, today my guest is someone whose brush with death from malaria as a young man in Africa led him to be obsessed not only with his own mortality, but more broadly with how all animals and plants thrive or die out in nature. Using data collected in the field, Tim Coulson, professor of zoology at Oxford University, develops mathematical models to explain and predict complicated ecosystems, like the consequences of the reintroduction of wolves to Yellowstone National Park, how little fish called guppies evolved differently in the streams of Trinidad, and the impact of climate change on wild sheep in the Outer Hebrides.

1:42Tim Coulson:When the young Tim was recovering from his bout of malaria, he promised himself that he'd write a complete guide to science. His ambitious book, A Little History of Everything, From the Big Bang to You, reflects his extraordinary ambition to comprehend the world. He says, lots of people in my area work on conservation projects or are trying to solve problems. I just want to understand how it all works. I always think that's a bit selfish. Well, I'd argue that we can't make the world a better place unless we understand how it works. Tim Coulson, welcome to The Life Scientific. Thank you very much.

2:17Tim Coulson:Now, when it comes to your own area of research, you've focused on the effect of animal predators. But it's more subtle than people think, isn't it? Because there are all sorts of feedback loops affecting both hunters and hunted. That's absolutely right. It turns out that predation, you know, the fact of one animal killing and eating another, has been incredibly important for the evolution of complex life over evolutionary time over the last four billion years. And why are the ecosystems that you study, particularly where there have been rewilding projects, for example, which you're going to come to, why are these so important to understand?

2:51One of the more complicated things that we can try to understand are ecosystems, because they consist of thousands of species from bacteria, fungi, plants and animals all living together. And trying to understand how they fit together and how those species interact is a challenge. And I think I was drawn to that challenge. You know, I just want to understand the natural world and how it works.

3:13Tim Coulson:But it's also so very complicated. Well, Tim Coulson, it sounds like you had a very happy childhood. You say you'd always been bonkers about science from as long back as you can remember. So I did have a very happy childhood and my parents were very encouraging. What I liked about maths and science is certainly the logic of both of them. And I really like that process of how we build up understanding through observations, through hypotheses, through experiments, but also through building mathematical models. And so initially I had a place to read maths at university, but I then went off to Africa for a year.

3:51So this was in Zimbabwe, your gap year. Yeah, I was fortunate enough to be accepted by an organisation called Project Trust to go off to Zimbabwe and teach in a rural school. And I remember one day going for a walk and sitting down and watching a herd of antelope, I think they were in parlor, walk past and thinking, you know, I don't think I want to be a mathematician. I'd like to be a biologist. And this was 1986, so before email. So I wrote to my parents saying, I don't want to do maths. Can you apply for me to go and do biology? I think if I'd been there, I'd have pretended the letter never arrived.

4:24But very kindly, they applied and York accepted me to study biology.

4:28Tim Coulson:You came back, you went to York to study biology, and as part of an undergraduate project, you head off on a second trip to Africa, this time to Kenya to work with the conservationist George Adamson. So firstly, for our younger listeners, can you explain why George was famous? George Adamson was an old-school conservationist, and earlier in his life, in the 1960s, him and his wife, Joy Adamson, had hand-reared a lion cub called Elsa, whose mother had been shot. And they raised this lion, and Joy, his wife, wrote a book about the lion, and it was picked up by filmmakers, and it became a very, very successful film.

5:09Tim Coulson:Born free. That's it, born free. Yeah, yeah. You're showing your age. And so I was lucky and a well-connected cousin wrote to George and said, I've got this fairly hopeless cousin. Would you be prepared to have him come over and do an undergraduate study on the behaviour of hand-reared and wild lines? And it was a terrible undergraduate project. Well, you say terrible, but you didn't get many interesting results. Well, it was underpowered because there were only three hand-reared lion cubs and there weren't very many wild ones. But it did actually end up teaching me a lot about statistics. Well, you did finish the project and then with your girlfriend, you hitched through Tanzania to Malawi.

5:56Tim Coulson:Now, two things happened while you were on this trip. One was that just a few days after you left his camp, George Adamson was murdered. I mean, that must have been hugely shocking for you. It was, and I didn't actually discover the news probably until between a week and two weeks since it happened. And it was through someone I was travelling with picking up an old newspaper and reading it out. It was shocking. That was the first, and I think probably the only person I've ever known who met a violent death. He was gunned down by a bandit. Wow. The other thing that happened on that trip seems to have crystallised your thinking about science in general.

6:33Tim Coulson:Tell me how you caught malaria. I didn't always interface with reality particularly well at that age. That's a great phrase. I had two types of tablets to take. I had my anti-malarials and I had water purification tablets. And I muddled them up. So I was dropping my malaria tablets into the water that needed treating before I drank it. And I was swallowing raw chlorine thinking I was treating malaria. Anyway, the water wasn't safe. I picked up a bug. I got quite ill. and during the time I was ill, I got bitten by a mosquito carrying malaria and I caught malaria, cerebral malaria. I mean, that must have knocked you for six.

7:10Tim Coulson:Coming on top of the shock of finding out that George Adams had been killed, I don't know whether you were near death's door yourself, but it was a serious bout, wasn't it? It was. In fact, I got on a plane to fly home and that's when things started to get quite serious. I got home and ended up being rushed into hospital fairly quickly. I don't remember any of it, but I remember after being discharged or as I was being discharged, the doctors saying, look, the next attack would probably have killed you. And that made me think, well, I should probably have some sort of aim in life other than just swanning around Africa enjoying myself.

7:42And by this point, I decided that religion wasn't for me. Made me decide I wanted to have a stab at understanding what science could tell us about why we exist. You say religion wasn't for you. Were your parents particularly religious? Yeah, my mum was and still is. And I don't think she's over the moon that I'm an atheist, but she's accepted it and she's very understanding.

8:02Tim Coulson:Well, you recovered and came back to finish your degree. So your next step was to do a PhD. And now you went to Imperial College London where you say you had a really fun time and formed lots of lifelong friendships. Your research project on the effects small mammals like squirrels have on the way trees grow, from seeds to saplings to fully mature plants, didn't pan out as well as you might have hoped if a comment from your supervisor is to be believed. That's right. So I had a wonderful time at Imperial College, made a lot of friends who I'm still close to. They described my PhD, summarised it as, where do squirrels hide their nuts?

8:43And I had two supervisors, Mick Crawley and John Lawton. But at the end of my PhD, Mick Crawley said, that's the second worst PhD thesis ever written after his own.

8:54Tim Coulson:Goodness me. well it can't have been all bad because you you were awarded your phd and as well as looking around after that for a research position you also applied to be a tv weatherman which sounds like a somewhat unusual choice what was your thinking i i needed to get a job and i hadn't got any publications from my phd which these days would would be the end of your career and i applied for pretty much everything because I needed some money. And I just remember the weatherman, I didn't even get an interview for that, but I did get an interview for a postdoctoral research position at the Institute of Zoology, the research arm of London Zoo.

9:34And that's where I ended up going.

9:35Tim Coulson:Well, Tim Coulson, your project was studying wild sheep on St Kilda. This is the westernmost islands of the Outer Hebrides off northwest Scotland. I gathered these sheep had been introduced there by the Vikings. So what was this project about? The sheep have been on the island for a couple of thousand years at least and they're a great system to study because it's a small island, an island called Hertha on the St Kilda Archipelago and the sheep can be caught, tags can be put in their ears so you can follow them throughout their lives. It's a very simple system, it's like a natural laboratory and the fact there's the sheep and there's vegetation and a few seabirds and some mice.

10:15And I was interested in understanding why numbers of animals changed over time, but also whether the effects of climate impacted different individuals as a function of their genes. So what did you find? We did find that the climate was changing, that winters were getting shorter, and that actually that was driving, not through evolution, but that was driving smaller sheep to actually survive the winter. There was more food around, and that meant on average sheep were getting a little bit smaller over time. So warmer, shorter winters, less harsh. Less harsh, less mortality, particularly of the smaller individuals.

10:50Right, right, right. On average, that meant that overall there was a decline in body size.

10:55Tim Coulson:Well, your research sparked an interest in the impact that ecosystems can have on how animals evolve. But I gather the ideas you were pushing, which linked ecology with evolution, were somewhat controversial. Why was this? Traditionally, ecology and evolution have been treated as different subjects. And ecology is thought to have happened quite quickly, whilst evolution plays out over much longer time periods. And so one of the things that, actually from my postdoc onwards, was to try and link the ecology and evolution. And that has been kind of driven by observations that evolution can happen really quite quickly through that mechanism.

11:33Tim Coulson:You then got interested in the effects of predators within an ecosystem, especially apex predators at the top of the food chain. That's right. So I was approached to ask whether I'd go and work on guppies in Trinidad, where when you remove the apex predators, you see ecological and evolutionary changes over a relatively small number of generations, sort of 10 generations to 30 generations. I want to talk about the guppies. They're tiny, small, colourful fish, aren't they? That's right. River fish. That's right. So a big guppy weighs a growl. They live their lives very, very quickly. You know, they live fast, die young.

12:09And the people who ran that project got in contact with me because I'd actually developed various mathematical and statistical methods that allowed us to analyse the sorts of data that they collect to investigate the role of apex predators and their removal.

12:22Tim Coulson:Interesting that you say that you were invited to get involved in this project because I think it's probably, at this point, good to clarify, Tim, the sort of work that you were and still are doing, in fact, because listeners might think you spend all your time out on field trips, observing the animals in the wild. But in fact, probably most of your work is at a computer screen, you know, developing, running highly complex mathematical models, doing lots of data analysis. That's right, Jim. So, in fact, I'm a fairly hopeless field worker, but don't tell anyone. My skill set is actually the analysis of data and then being able to take the statistical analyses that come out to construct reasonably realistic models, mathematical models of the ecosystems we're analysing, and then to simplify those models to identify general principles.

13:08Tim Coulson:But certainly that was something that you'd built up a reputation in by this point, which is why you get invited to work on these new projects. So tell me a bit about the guppies study in Trinidad. What was it that you were interested in looking at? The guppies are really interesting because if you start at a stream in low levels, low altitudes in Trinidad, in the north of Trinidad, you find guppies that live with predators, apex predators that will eat them. But if you walk up the same stream and climb up a waterfall, there are no predators, but sometimes you'll find guppies. And the guppies look very different and they live very different lives.

13:41And work by people like David Resnack and John Endler had actually shown that if you take guppies that live with predators and you put them above the waterfall and you leave them there, they will evolve into this low predation type. And so a study had been set up where guppies were captured every month and each time a new guppy was caught it was tattooed and then released. And they generated a huge data set across four streams that allowed us to look at the evolutionary journey that guppies take from being released from living with predators to evolving to be very, very good at living with lots of other guppies when food becomes scarce.

14:21Tim Coulson:Well, a related project to this, in terms of your findings, was the study of birds living on Heron Island on the Great Barrier Reef. Tell me how that came about. My wife, Sonia Clegg, that's actually her study. And we were married and it made sense to work together on this because I could bring some of the modelling involved. And this is a system that's a bit like the guppies in many ways in the fact that the birds, when they live on the mainland of Australia, live with predators, things like magpies, snakes, possums and whatever, that can particularly eat the nest, and there's birds of prey. But these birds often colonise oceanic islands, and when they colonise there, over the course of thousands of years, and this is slow evolution waiting for mutations to arrive, they kind of evolve to be larger, which is what the guppies do in the streams when they live without predators, and they fly less, they change their song, they become much more aggressive.

15:16So we see a very similar pattern, believe it or not, in the guppies, which evolve quickly, and in these birds, silver eyes, that evolve much more slowly.

15:23Tim Coulson:So in both cases, with the guppies and the birds, without predators, they grow bigger, have longer lifespans. Surely this is pretty much what we might expect to see, right? Well, except if you take large animals that live with predators and you put them in an area where there are no predators, so things like elephants, they shrink. They evolve to be much, much smaller. And that's something known as the island rule or Foster's rule. And there's a huge number of hypotheses that people have put out there as to why this occurs. Some of them involve predators, some of them involve climate, some of them involve competition.

16:00And what really seems to be happening in each of these systems is that something has to kill you. And the cause of death is critical. So a lot of our work is trying to find out when and why you see these ecological and evolutionary changes. So why are these studies important? Across much of the world, predators are in decline because we're not very good at living with them. And we want to know what the consequences are, both ecologically and evolutionary, of removing predators. Because once they're gone, we're not going to be able to bring them back.

16:36Tim Coulson:We're moving on to predators now because if wild sheep, tiny birds and even tinier fish don't sound particularly sexy, let's talk about the wolves of Yellowstone National Park. You were initially invited over there on holiday with your kids. That's right. In 2009, 2010, I spent a year in Stanford with the family and I was writing down some new theory at the time. and we were going to Yellowstone and my then wife suggested I write to them. She said, you're a biologist, you must know someone. So I wrote to them dutifully and said, you don't know who I am, but I'm a biologist. We're coming to Yellowstone, it would be great to meet.

17:15And they said, oh no, we do know who you are and we were going to write to you because we'd love you to model our system.

17:21Tim Coulson:OK, so unlike the guppies and the birds, the silver eyes that you were studying on Heron Island, wolves are the predators now. What has been the consequence? of their reintroduction into Yellowstone? Wolves were driven extinct in Yellowstone in the 1920s, along with mountain lions and grizzly bears, deliberately. Wolves were absent from the landscape for 70 years before the reintroduction occurred. Mountain lions and bears came back naturally. And since the return of wolves, there have been changes in Yellowstone. We've seen a very significant decline in elk on the northern range, about two-thirds, so elk are a big deer-like species.

17:59We've seen bison numbers go up. And in some areas of the park, we've started to see trees coming back. But people argue about the role of wolves and the role of mountain lions, the role of climate change, the role of bears, the role of disease, the role of people. And, of course, we can't do the experiments there because we've just got one yellow stone. Yeah, right. So that's where modelling comes in because we can build models of these ecosystems. We can then use those models to tease apart the relative contribution of wolves and mountain lions. And that's what some of the stuff we're doing at the moment.

18:29We're building these complicated models for Yellowstone. How is it that you use the data then to feed into your computer models? The approach that I take is kind of referred to as demographic. So there are a few fundamental biological processes. So birth and death and development and inheritance are key. And so the models that I build explain how each of those processes is influenced by, say, the weather, the number of prey, the number of predators, the diseases that are on the landscape.

18:58Tim Coulson:It's quite complex mathematics, isn't it? You say there's only one real Yellowstone, but with a computer simulation, you can run it again and again and again with different inputs to see how things end up at the other end. That's right. And we also try to simplify the models to see if we can get to generality. So the models at that point don't start to describe exactly what goes on in the ecosystem particularly well, but they might catch a key feature of the ecosystem, like the fact that wolves drive down elk numbers or cause what's called a trophic cascade. It's a wonderful job because I get to mix going to the field and thinking about these animals with building mathematical models and analysing data.

19:40Tim Coulson:And in the real Yellowstone, not in your computer model, it's obvious that reintroducing wolves is going to drive down the elk population. But wasn't there talk of one of the consequences of this reintroduction of the wolves has been to change the river flow in Yellowstone, which is sort of... Has it been debunked? It's a very popular YouTube video, but the narrative we all buy into is largely incorrect. That's not to say that wolves haven't had an effect. They have, but it's subtle and it's complicated, and we shouldn't be surprised at that because the ecosystems contain vast numbers of animals interacting in many ways.

20:17Wolves don't just eat elk. They'll kill pretty much anything they can. They'll scavenge bison. They're competing with the mountain lions. And also the argument that people think they know about Yellowstone is that forests have recovered. Forests don't recover overnight. It takes decades.