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David Tilman is a leading ecologist and a source of deep knowledge about biodiversity and the benefits that society receives from natural and managed ecosystems. As part of the work I do for the food-awareness organisation ProVeg International, I spoke to David about the basics of biodiversity and the ways in which biodiversity loss threatens both human civilisation and the natural world, as well as the relationship between biodiversity loss and the broader environmental crisis.
PM: Hi, David, thank you so much for joining us.
DT: It’s my pleasure.
PM: Thank you. I’m Peter Machen for ProVeg and we’re talking to David Tilman today about biodiversity and the threats to biodiversity, with world biodiversity day coming up.
David, I’m going to begin with two very simple questions. The first is, although the issue of biodiversity is increasingly entering the mainstream, I suspect that a lot of people don’t fully understand the concept or its broader implications. Can you talk a little bit about what biodiversity is and why it’s so important?
DT: Well, biodiversity refers to all the different kinds and forms of species there are on Earth. So all the different kinds of plants of mammals, birds and so on. And its importance has only been really thoroughly studied and discovered in the last two decades.
We now know that the single most important factor determining how an ecosystem operates – how productive it is, how reliable and stable it is and so on – is the number of different kinds of species living in it. Biodiversity turns out to be the key to why the world functions in the ways that we need it to function for us to have good lives on Earth.
PM: OK. That is very interesting, just the way you phrase it. The same seems true about our bodies as well, which is also something we’ve only learned in the last 20 years – that the greater the biodiversity in our bodies, the healthier we are.
DT: Right. That’s true. The whole microbiome, the work on that, and the diversity of other organisms with us. There’s a very simple reason why the world now has so many species. Each species was able to differentiate itself from what it was originally to become something new, a new species, because it did something better in that new form than any other species on earth could do.
DT: Each species is a specialist – it’s like a profession. Each kind of doctor has a different skill and is important in our healthcare system. And each other profession in our economy does something unique that no other profession can do. Each species is a unique profession for life on earth. If you lose a species, you lose that efficiency.
PM: That’s kind of beautiful. It relates very much to a question I’m going ask you towards the end. So, now that we’ve established what biodiversity is, and hopefully its implications – because that is key for me – can we talk about some of the ways in which biodiversity is under threat around the world?
DT: Well, species have habitats they live in that they’re specialised at living in. And 40% of all the land on earth has now been taken over by agriculture. So, one species – humans feeding ourselves – have displaced whatever used to live on 40% of the land on Earth. And that is the single biggest threat to biodiversity – our food system. The more land that we need to feed ourselves, the more that we threaten the functioning of the ecosystems on earth that we also need to provide us with lots of goods and services.
PM: Does that 40% include all pasturing, all arable land, all agricultural land, all planting, everything?
DT: It includes arable land and pastures. It does not include, say monocultures of trees that we use to produce timber. That would add some more land to that number. It doesn’t include roads and cities and highways and so on.
DT: But that is the single largest use of land by people. And it’s the use that is likely to expand greatly if we keep living the way we are living and having diets that are unhealthy for the planet and unhealthy for us.
PM: So, I’m going to cut short to another question that I wanted to ask. If we drastically reduced our meat consumption – if say, hypothetically, the entire middle class of the planet reduced their meat reduction by 50% – would that have a huge impact?
DT: Absolutely. The amount of land we are likely to clear destroy ecosystems to create new cropland and new pastures is huge around the world. And that would threaten almost all the remaining large mammals on earth, for instance, with extinction.
And that is mainly driven by the greater consumption of meat than many people do when they become more wealthy. So, the poorest countries in the world have their incomes going up right now; they’re demanding more meat; more land is being cleared; and because of that, more and more species are getting closer and closer to extinction.
So if we, if we could cut meat in half, if we could eat half the meat we eat right now, especially ruminants, especially beef, that would have a huge long-term benefit for our health and for the health of all the ecosystems on earth.
PM: Interestingly, what that would mean in most Western countries is simply that people eat what their government advises them to on their ‘food plates’ or ‘food pyramids’. Because I think in most of the West, people eat twice what they’re supposed to, according to very conventional measures.
DT: Yeah, there is a great overconsumption of meat by most people. Most people imagine they need lots and lots of protein in their diet. In fact, you can get all the protein you need by having a grain-based diet without any meat at all.
PM: Yeah. Yeah. Yeah. So when people make the appeal to protein as being so important, it seems to me that the only time we really suffer protein deficiency is when we suffer malnutrition generally. I know you’re not a medical doctor, but is that roughly true?
DT: No, that is true. I’m not a medical doctor but I’ve collaborated with really excellent nutritionists. And in the sixties and seventies, nutritionists thought many people were ill or malnourished for lack of protein. But an immense amount of research that was done then showed that wasn’t the case. Now, red meat has a value but the value is not for protein. It’s that it has iron and vitamins in it that are hard to get in other ways.
So, it turns out that what people thought was a disease caused by a lack of protein was actually caused by a lack of micronutrients and lack of vitamins.
David Tilman is a leading ecologist and a source of deep knowledge about biodiversity and the benefits that society receives from natural and managed ecosystems. As part of the work I do for the food-awareness organisation ProVeg International, I spoke to David about the basics of biodiversity and the ways in which biodiversity loss threatens both human civilisation and the natural world, as well as the relationship between biodiversity loss and the broader environmental crisis.
PM: Hi, David, thank you so much for joining us.
DT: It’s my pleasure.
PM: Thank you. I’m Peter Machen for ProVeg and we’re talking to David Tilman today about biodiversity and the threats to biodiversity, with world biodiversity day coming up.
David, I’m going to begin with two very simple questions. The first is, although the issue of biodiversity is increasingly entering the mainstream, I suspect that a lot of people don’t fully understand the concept or its broader implications. Can you talk a little bit about what biodiversity is and why it’s so important?
DT: Well, biodiversity refers to all the different kinds and forms of species there are on Earth. So all the different kinds of plants of mammals, birds and so on. And its importance has only been really thoroughly studied and discovered in the last two decades.
We now know that the single most important factor determining how an ecosystem operates – how productive it is, how reliable and stable it is and so on – is the number of different kinds of species living in it. Biodiversity turns out to be the key to why the world functions in the ways that we need it to function for us to have good lives on Earth.
PM: OK. That is very interesting, just the way you phrase it. The same seems true about our bodies as well, which is also something we’ve only learned in the last 20 years – that the greater the biodiversity in our bodies, the healthier we are.
DT: Right. That’s true. The whole microbiome, the work on that, and the diversity of other organisms with us. There’s a very simple reason why the world now has so many species. Each species was able to differentiate itself from what it was originally to become something new, a new species, because it did something better in that new form than any other species on earth could do.
DT: Each species is a specialist – it’s like a profession. Each kind of doctor has a different skill and is important in our healthcare system. And each other profession in our economy does something unique that no other profession can do. Each species is a unique profession for life on earth. If you lose a species, you lose that efficiency.
PM: That’s kind of beautiful. It relates very much to a question I’m going ask you towards the end. So, now that we’ve established what biodiversity is, and hopefully its implications – because that is key for me – can we talk about some of the ways in which biodiversity is under threat around the world?
DT: Well, species have habitats they live in that they’re specialised at living in. And 40% of all the land on earth has now been taken over by agriculture. So, one species – humans feeding ourselves – have displaced whatever used to live on 40% of the land on Earth. And that is the single biggest threat to biodiversity – our food system. The more land that we need to feed ourselves, the more that we threaten the functioning of the ecosystems on earth that we also need to provide us with lots of goods and services.
PM: Does that 40% include all pasturing, all arable land, all agricultural land, all planting, everything?
DT: It includes arable land and pastures. It does not include, say monocultures of trees that we use to produce timber. That would add some more land to that number. It doesn’t include roads and cities and highways and so on.
DT: But that is the single largest use of land by people. And it’s the use that is likely to expand greatly if we keep living the way we are living and having diets that are unhealthy for the planet and unhealthy for us.
PM: So, I’m going to cut short to another question that I wanted to ask. If we drastically reduced our meat consumption – if say, hypothetically, the entire middle class of the planet reduced their meat reduction by 50% – would that have a huge impact?
DT: Absolutely. The amount of land we are likely to clear destroy ecosystems to create new cropland and new pastures is huge around the world. And that would threaten almost all the remaining large mammals on earth, for instance, with extinction.
And that is mainly driven by the greater consumption of meat than many people do when they become more wealthy. So, the poorest countries in the world have their incomes going up right now; they’re demanding more meat; more land is being cleared; and because of that, more and more species are getting closer and closer to extinction.
So if we, if we could cut meat in half, if we could eat half the meat we eat right now, especially ruminants, especially beef, that would have a huge long-term benefit for our health and for the health of all the ecosystems on earth.
PM: Interestingly, what that would mean in most Western countries is simply that people eat what their government advises them to on their ‘food plates’ or ‘food pyramids’. Because I think in most of the West, people eat twice what they’re supposed to, according to very conventional measures.
DT: Yeah, there is a great overconsumption of meat by most people. Most people imagine they need lots and lots of protein in their diet. In fact, you can get all the protein you need by having a grain-based diet without any meat at all.
PM: Yeah. Yeah. Yeah. So when people make the appeal to protein as being so important, it seems to me that the only time we really suffer protein deficiency is when we suffer malnutrition generally. I know you’re not a medical doctor, but is that roughly true?
DT: No, that is true. I’m not a medical doctor but I’ve collaborated with really excellent nutritionists. And in the sixties and seventies, nutritionists thought many people were ill or malnourished for lack of protein. But an immense amount of research that was done then showed that wasn’t the case. Now, red meat has a value but the value is not for protein. It’s that it has iron and vitamins in it that are hard to get in other ways.
So, it turns out that what people thought was a disease caused by a lack of protein was actually caused by a lack of micronutrients and lack of vitamins.
PM: Yeah. So just to clarify, the fact that biodiversity is threatened, say, compared to the 1950s or the 1970s – I was born in 1971 – and it’s not just that we’re beginning to lose biodiversity – a huge amount has already been lost during my lifetime. Is that correct?
DT: That is correct. If you look at the normal rates that species have gone extinct at around the world, for every million species you lose about one species in a year. And we are losing 20 to 40 times that amount right now. And that’s a very conservative estimate based upon the real well-documented loss of species.
But that’s nothing compared to what will happen if we continue on our rapid land-clearing trajectories around the world. Because we now have the countries with the greatest growth in population and the greatest growth in income living in the tropics and those tropical countries are where the storehouse of global biodiversity is located.
PM: Yeah. Yeah. Yeah. I’m from South Africa and I think Cape Town actually has the most most concentrated source of biodiversity in the world – in terms of plant life at least. I don’t know if that’s true, but that’s one of their claims.
DT: No, it’s very true. The fynbos is amazing.
PM: Yeah. And it’s beautiful. When you go up there you can smell it as a collective kind of thing. Yeah, it’s really wonderful.
So, this is a big question but it seems to me that systemic change on a global scale is needed, not just in our diets, but in most areas of human activity, if we are to address the core challenges of biodiversity. Is this true or is this an overstatement?
DT: No, it’s very true yet there are eight billion of us and we demand about 15 times more crops to be produced for each of us than we actually eat. Some of it we waste. Much of it we give to livestock that eats it and then we make milk and eggs and chicken and beef and pork and so on. And so we have an immense demand that way and we demand an immense amount of energy. And whenever eight billion people demand something, there are global consequences.
And the other thing is, you might think, “Well, eight billion people is a problem. We have too many people”. And that is a problem. But the even bigger problem is that we are richer, we demand more. The typical person right now has 60 times the buying power that we had in the year 1850. Each of us is demanding 60 times more goods and services from our economy. And we have to make sure each of these major items that we buy is being produced in a sustainable manner. Otherwise, we will just destroy the future of Earth as being a good place for humans to live.
And let me tell you, there’s no other planet we’re ever going to live on. This is it.
PM: Yeah, yeah – and it’s an old kind of t-shirt cliche – but even if there was another planet for us to live on, there’s no other planet with chocolates and kittens.
DT: No this is it. There is no other place we’ll ever make it. This is our only chance.
PM: Yeah. Mars doesn’t float my boat anyway. I mean, it looks beautiful. I’d like to go for a day, but not forever! I’m kind of going on a tangent a little bit here but I often read about or hear people talking about, how, you know, the planet will just eject us and it will recover. But I don’t think it’s that simple….
DT: Well, if you look at the long history of life on earth, recovery, the evolution of new species to make up for ones that went extinct after a mass-extinction event, that’s a 10-to-30-million-year process. So, it’s, uh, it is ridiculous to imagine that everything will be all right in only 30 million years. We really have to do something now.
PM: Yeah, totally. It makes sense – because we’re here now. And this planet is so beautiful. I mean, just on a personal level, just the fact that koalas are threatened with function extinction! Giraffes! It’s just ludicrous. It’s just crazy.
DT: Oh, I agree. And you look at what people do. What do we do when we have time off? We go to nature. We go to national Parks. We go to beaches. We swim and look at the fish and so on. We look at birds. We love nature. We are part of nature and it has been a part of our life forever. And yet when we live in cities and shop in grocery stores, we don’t realise that some of the foods we are buying are causing animals to go extinct and plants to go extinct all around the world.
PM: So, something that I’ve been wondering for quite a while now is what would happen if we collectively came to the realisation that, actually, we are animals, we are part of this, we are not separate, and all of life is interconnected – socially, politically, biologically. For me, that is the thing we need to realise, not just know but realise and feel in order for things to change. And it seems to me that a fundamental shift in human perception is needed.
DT: Well, that would really help. I mean, we, have traditions, laws, beliefs, cultural aspects that have been formed over hundreds of thousands of years. But almost all of those formed when we were having a minor environmental impact, where what we did really didn’t change the world. And it has only come about that we’re having this kind of large impact since around 1900. And it’s been exploding. Our impact has been exploding since then. And so it’s very hard to realize how many things we need to change and how we need to change them.
And you can’t expect eight billion people on earth to know what you and I know Peter. We dedicate our lives to these kinds of issues. They’re just trying to live their life. And so we have to have some way that we regulate our economy so that the goods and services people want and need are being provided in a way that helps them but also helps preserve the livability of Earth.
PM: So right now because your time is limited and because this is a kind of relatively short-form format that we follow, I just have two more questions, both kind of obviously related to what we were talking about. My first is: what are key government actions that can be taken to mitigate or deal with the threat to biodiversity?
DT: It really depends upon the nation and its history. Some nations, like the United States, have destroyed a large amount of its biodiversity, and others were lost when people first spread across the continent and large animals went extinct 10,000 years ago. But for the countries which are not as wealthy and have a future of more rapid development, they could do an immense amount of good to preserve biodiversity by asking what kinds of ecosystems do they have. How could we save some? Where should we focus our development that we have to have in order to feed our people? On what lands? And what lands can we save? Because, as it turns out, there are two main reasons why species are threatened with extinction: One is that land is cleared, and the other is that the uncleared land that is left is scattered about in little pieces here and there. If they were all left in one spot, sort of like a large national park, you could preserve an immense amount of biodiversity that you lose in all these little tiny pieces that we tend to leave behind when we develop land.
So that’s a number one for a government: to plan their land future, plan how they’re going to let land be used and what land they’re going to preserve. They have to do that now, before that land is cleared because it’ll never go back to nature.
PM: Yeah. So, I think there’s a relatively recent example of that, that didn’t work out very well. I’m maybe wrong about the detail but I’m pretty sure that it was Ecuador, which, three or four years ago, asked the world to pay it for not mining its forests – think part of the Amazon is in Ecuador – and they didn’t want that much. I think they needed like $3 billion or something, and they didn’t get a cent.
DT: Well, that’s, I don’t know that story but a lot of the conservation has gone on. For instance, in Costa Rica, which has an amazing set of national parks that preserve lots of tropical biodiversity, that was started because governments around the world were willing to forgive the debts of Costa Rica in exchange for Costa Rica saving land. It was an incredibly big bargain for the world that so much biodiversity was preserved at what was really such a small cost.
And we have to realize that we in wealthy countries are the original sinners. We’ve already done these things to the lands in our country and we would be hypocrites to imagine that more developing nations should be able to do this all on their own without our assistance.
PM: Yeah! So there’s something from what you said that stuck out. You said, “Once the land is developed, it’s never going back”. So is rewilding a thing? Does it work if it’s possible, if it’s politically feasible? Is rewilding one of our solutions?
DT: Rewilding could help. And I think I’m sort of a radical in another way. I think, if we go to continents like North and South America, which have lost almost all of their large animals in a big extinction event 10,000 years ago, we can’t rewind them with the original species. But species have migrated from one continent to another many, many times over in the last 10 million years and we could bring in species that are threatened, let’s say in the southern part of Africa or in South Asia, into comparable climates, comparable vegetation – not the species, but the basic form – and establish rewilded high-diversity ecosystems that would be one more piece of armour in our desire to preserve this biodiversity forever.
PM: Yeah.
DT: So that’s a wild radical thought. But I think we should do it.
PM: I think it’s a great thought and the idea of ‘natural systems’ is so totally over in a way. Obviously, it would have to be done very carefully – and by experts – because it could also go wrong…
DT: It could. But it turns out if you look at the history of movement of species from one continent to another, there’s almost no case where even a large number of new species migrating into a new continent ever caused the extinction of the existing species. They competed and they became rarer – the existing ones became rarer – that always happens. But it’s never caused extinction. So, that is true for when new predators come in, when new herbivores – plant-eating animals – come in, and so on, and when new plants come in. All those things have been recorded over and over, over millions of years, and we see that. So I think there’s reason to believe it’s unlikely to be massively disastrous.
PM: Ok. So even when we introduce the disaster, it still doesn’t lead to extinction-level events. It just makes things messy for ourselves and...
DT: Yeah, there are new species we’ve introduced which have been a pain. Often they’re a problem because we introduce them without their natural enemies.
PM: Ok! My very last question for you is – I almost don’t want to ask it in case the answer is negative – but can individuals make a difference? And how can we make a difference?
DT: Absolutely. Ultimately, what happens on earth comes down to the choices that each of us make. And so, when you’re buying a new vehicle, try to get one that has the best efficiency for fuel. And now, if you can, maybe get one that is electric, which is an even better thing to do. In our homes – a lot of energy is used in homes – purchasing an appliance that is highly efficient in how it uses energy is another very important thing to do.
And then, lastly, one of the big things we consume that has a huge impact is food. So, don’t waste food and eat food that’s lower down the food chain. Increase the number of grains, whole grains, vegetables, and fruits that you eat – and eat less meat. You don’t need as much meat; almost no one needs as much meat as they’re eating. And the grains that you substitute for it are healthier for you and are much better for the environment. So, basically, being efficient in our use of energy and being efficient in our use of food are the two things that each of us should do.
PM: And of course, those actions don’t just benefit biodiversity, but they benefit the whole…you know, obviously climate change, and the planet, and a whole range of other things.
DT: And they benefit your health. Not just do you live longer but you live longer with less disease. Diseases like diabetes aren’t just a problem because you have to take insulin and so on. They’re a problem because they degrade the quality of your life. My grandmother died of diabetes. She went blind. She, you know, you can start having trouble with blood flow to the feet and so on and have to have parts of you amputated – it’s really a horrible disease. And we can avoid it – it’s a totally avoidable disease. With the right diet and exercise, none of us have to get type 2 diabetes.
So, I think that there is a massive win-win that people aren’t thinking about.
PM: Yeah. Well, that is a wonderful way to end our conversation! Thank you so much for talking to me, David.
DT: It’s been a pleasure, Peter.
PM: Okay. Thank you very much.
David's Wikipedia page | David's Twitter account | David's Google Scholar page | David's published research at Research Gate
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A rich text element can be used with static or dynamic content. For static content, just drop it into any page and begin editing. For dynamic content, add a rich text field to any collection and then connect a rich text element to that field in the settings panel. Voila!
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A big thank you to Kirsten Machen and Linda Leow for both suggesting, within days of each other, that I start interviewing people again, and also for the numerous feedback requests. Thanks also to Debbie Sykes for some on-point UX suggestions and to Lorna McDowell for the frequent iPhone testing. Thanks to Sharlene Versfeld and Nashen Moodley for helping me to get access to so many amazing people over the years, and to Mirah Von Wicht for all the hugs and support. Special thanks to all my past editors, especially Cyril Madlada, for his immediate faith in me, Debbie Reynolds, for some wonderful working years at the Independent on Saturday and for giving me free reign to produce such eclectic content, and to Yves Vanderhaeghen at the Weekend Witness for doing likewise. And, of course, a massive thank you to everyone who has spoken to me over the years. And finally, warm and appreciative thanks to YOU for reading, watching, and listening, and to my mother Astrid Machen for her boundless and endless love and encouragement.
A big thank you to Kirsten Machen and Linda Leow for both suggesting, within days of each other, that I start interviewing people again, and also for the numerous feedback requests. Thanks also to Debbie Sykes for some on-point UX suggestions and to Lorna McDowell for the frequent iPhone testing. Thanks to Sharlene Versfeld and Nashen Moodley for helping me to get access to so many amazing people over the years, and to Mirah Von Wicht for all the hugs and support. Special thanks to all my past editors, especially Cyril Madlada, for his immediate faith in me, Debbie Reynolds, for some wonderful working years at the Independent on Saturday and for giving me free reign to produce such eclectic content, and to Yves Vanderhaeghen at the Weekend Witness for doing likewise. And, of course, a massive thank you to everyone who has spoken to me over the years. And finally, warm and appreciative thanks to YOU for reading, watching, and listening, and to my mother Astrid Machen for her boundless and endless love and encouragement.
A big thank you to Kirsten Machen and Linda Leow for both suggesting, within days of each other, that I start interviewing people again, and also for the numerous feedback requests. Thanks also to Debbie Sykes for some on-point UX suggestions and to Lorna McDowell for the frequent iPhone testing. Thanks to Sharlene Versfeld and Nashen Moodley for helping me to get access to so many amazing people over the years, and to Mirah Von Wicht for all the hugs and support. Special thanks to all my past editors, especially Cyril Madlada, for his immediate faith in me, Debbie Reynolds, for some wonderful working years at the Independent on Saturday and for giving me free reign to produce such eclectic content, and to Yves Vanderhaeghen at the Weekend Witness for doing likewise. And, of course, a massive thank you to everyone who has spoken to me over the years. And finally, warm and appreciative thanks to YOU for reading, watching, and listening, and to my mother Astrid Machen for her boundless and endless love and encouragement.
A big thank you to Kirsten Machen and Linda Leow for both suggesting, within days of each other, that I start interviewing people again, and also for the numerous feedback requests. Thanks also to Debbie Sykes for some on-point UX suggestions and to Lorna McDowell for the frequent iPhone testing. Thanks to Sharlene Versfeld and Nashen Moodley for helping me to get access to so many amazing people over the years, and to Mirah Von Wicht for all the hugs and support. Special thanks to all my past editors, especially Cyril Madlada, for his immediate faith in me, Debbie Reynolds, for some wonderful working years at the Independent on Saturday and for giving me free reign to produce such eclectic content, and to Yves Vanderhaeghen at the Weekend Witness for doing likewise. And, of course, a massive thank you to everyone who has spoken to me over the years. And finally, warm and appreciative thanks to YOU for reading, watching, and listening, and to my mother Astrid Machen for her boundless and endless love and encouragement.
