How Concerning Is Biodiversity Change?

00:00:00: Pereira: We tend to focus sometimes on on the negative things. And there is a lot of negatives about what's happening about versus change. And we don't sometimes look at what have been the positive aspects I've seen in my lifetime. Biodiversity improve in many areas around me, and I've seen species that were extinct, locally extinct, that they've come back and rivers that were dead coming back to life. And that's because there's been so much positive developments from environmental policy in Europe and in other countries in the world, and there is a lot of hope, and I think there is a lot of hope as we go forward that we can improve the situation in the future.

00:00:53: Hahn: Welcome to Inside Biodiversity. This podcast is hosted by iDiv, the German Centre for Integrative Biodiversity Research. My name is Volker Hahn. I am head of the communications unit at iDiv. And my guest today is Henrique Miguel Pereira. Henrique is a colleague of mine. We work in the same building. He is head of the Biodiversity Conservation Research Group at iDiv, and he's also a professor at the Martin Luther University Halle-Wittenberg. His expertise includes biodiversity conservation, ecosystem restoration, biodiversity monitoring and biodiversity change, among other topics. And today we will focus on biodiversity change. Welcome to the show, Henrique.

00:01:42: Pereira: Thank you. Thank you for for having me.

00:01:45: Hahn: Let us begin. Can you briefly tell us who you are and why do you research? Biodiversity and biodiversity change.

00:01:55: Pereira: I've always been interested as a young adult in nature conservation. I became interested in the extinction crisis. And that was, let's say, the big focus of biodiversity conservation in the 1990s and early 2000. And that has really led to much of my work, not always in goal, biodiversity change topics, but it was really triggered by this realisation that we were losing species that were not coming back. That was, let's say, what really got me into the field as an as an ecologist, as a researcher, and that has driven a bit on my research and then also the interest in, okay, now we know that this is happening and we know what is causing it. What kind of policies can we put in place to improve the situation to avoid the loss of the species? So that also has driven my interest in science policy. And although most of my research research is is basic research, I've done a lot of science policy work at the international level, both for the Convention on Biodiversity but also at the European level, working with the European Commission, even also at the national and local level. I've worked with like, uh, cities, I have I've, I've helped develop the biodiversity plan, for instance, for the city of Lisbon about ten years ago. Yeah.

00:03:30: Hahn: Okay. So you you mentioned biodiversity and species losses that got you into researching biodiversity. Some of the ideas surrounding that were challenged in the in the 20 tens. There were a couple of studies that showed that biodiversity is not declining everywhere, at least when you look at the number of species this was, people looked at time series of species richness, which is the number of species. And they found that in some places. It goes down and others it goes up, and some it stays the same. And, uh, while almost everywhere we're observing that the identity of species is changing. These studies got a lot of attention. How did you experience these studies and how did you react?

00:04:24: Pereira: Okay. First let me try to explain that there are different ways of measuring biodiversity. There are different metrics, and there is also different scales at which you measure measure these metrics. The number of species is one metric. It could be other metric could be the ranges of the species, or it could be the size of the populations of species and combinations of these. And then you can measure these at a local scale for a second. Go and and count the species in my backyard or in a plot. Or I can look at the change of the species in a country in or at, let's say, at the global level. So you can measure the number of species or any of the other metrics at different scales. I think that the, the result at the number of species is declining globally, and that we have around 1% of extinctions of vertebrates and documented over the last 500 years. That number has not been questioned. And I must say that this is what really got me into this research. What has driven a lot of the conservation agenda is this global loss of species. Now, a different question that you can ask is What is happened to the number of species in a place in your backyard, you know, around your city or your municipality? What what is happening to the number of species at the local scale? And there is where the current research has, let's say, led to some some controversy and some questions. So again, it is not a direct consequence that you are losing species globally, that you also are losing species locally. And but it was.

00:06:37: Hahn: A surprise right.

00:06:39: Pereira: Yeah. But but it was a surprise because.

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00:07:34: Pereira: It was a surprise because in the 1990s there was a field that was developed called Biodiversity Ecosystem Function, that was based on the idea that we had this global loss of species, and this was affecting the way that ecosystems were functioning, that they were affecting. And there was a lot of research. that started looking at if you change the number of species in the plot, what happens to ecosystem functions like, let's say, primary productivity. And and people are starting to find research. We're trying to find that if you knock out species and a relatively large number of species. So if we reduce the diversity of a plot by 50%, you do have an impact on ecosystem function.

00:08:23: Hahn: So that means if there are less plants, plant species on a on a given plot, the the grassland grows slower.

00:08:31: Pereira: Grassland grows slower. And another metric that people have looked at, for instance the resilience to drought also decreases. And so the other the inspiration for these studies on biodiversity function comes from the global loss. No one has been documented. A lot of local species richness declines. yes, we know that, you know, when some habitat conversion happens. And for some groups there is some species that does it, but there is also some species that show up, particularly for example, our species. There's something about this very and you can have a genius change. So it is perfectly possible to have a situation. We have a few species that have disappeared over the last but five years. Number of species. Okay. But in my book did I notice that in my in my in my place or in my backyard? Well, the species was never here in my backyard, so maybe I have not noticed it. And maybe the best comparison is the carbon concentration. The atmosphere is increasing everywhere because everything is being mixed. But in biodiversity, because a lot of the drivers act locally, what happens here may be very different from what happens in. Well, certainly in the Amazon. But what happens here, let's say, in Leipzig, may be very different already from what happens outside Leipzig. And so what does it mean this to measure local species, which is what is the relationship between the local species richness and regional global species richness? It's not linear at all. This relationship is not. We we indeed know that this has been modelled. There's been an analysis. Theoretically, it's highly nonlinear. The relationship between what happens at the local scale and the global scale. It's not an average. It's a fundamental difference between species richness. And let's say for instance, temperature. If I want to to measure this global change in temperature, I can measure the temperature in 2000. Average temperature daily everywhere I'm measuring all the grid cells of the planet and I calculate the mean. And that gives me the global mean change in temperature in 2010. If I calculate the mean in 2000, 2020 ten, I can get the difference, the decadal difference by just average local temperatures. If I do the same thing with species richness and I get I measure in each grid cell the species which is in 2000 and the species in 2010, I subtract species regions from 2000 to by the species region from 2010, and I do the average globally. I don't get the global change in species richness. There is a non-linear relationship and so there is not. This doesn't need to be related. When the field was created by the same function, when they they were inspiring by this work, but they there was not a global analysis saying that the local species richness was changing. It was just saying, oh, this may be happening. And then when the studies are published in 2014 and 2013 of time series, and that they don't find in time series trends in local species richness. This is this. Yes. This was took a lot of the community by surprise, but mainly mainly the community college ecosystem function community and not so much the conservation community. The conservation biologists had been working on on analysing patterns of biodiversity change. They were never ranged in local species richness trends and it was never a metric. It was very popular in in most indicators that biodiversity conservation scientists were using. It mainly took by complete surprise the people working on biodiversity function and the people working on, on on community ecology. And it was also, let's say, a very interesting result and exciting result also for the conservation scientists. But not not completely surprising. Yeah.

00:12:56: Hahn: Yeah. So, um. Also, some researchers were reluctant to to accept these, uh, results. And they've been challenged by other studies and other papers criticising, uh, for example, a, um, uh, sampling bias. Much of the data comes from, from well-studied regions, for example. So there is still this controversy. Where's your position there. Do you do you consider yourself as being part of a camp? Do you think the the the results are valid or should they be treated with with more, more carefully?

00:13:36: Pereira: I think it's a fascinating topic. If you ask me, do we know what is the global mean of local regions, the global mean of the trends in local regions? Is it negative or zero or even positive? I would say we don't know the answer. I would even start by saying what does it mean? This calculation. What is it telling you about biodiversity change? Because if you're looking at certain drivers, they didn't reach a large part of the globe. What we're talking about 40 or 50% of the globe, they have not been reached by some of these drivers in the last century. Yeah. And this is where the problem starts, because the analysis that shows that you are referring to that was were published by Meridor and colleagues called the bio time data set. And Mark Whelan and colleagues and and based on plant plant plots. None of those analysis of time series were particularly looking into regions where the changes have happened And in the localities the changes have happened. So they have these what we call the the parking lot problem. If an area was converted into a parking lot from a beautiful native forest or native grassland, the scientists didn't go there and count it again. The plant species there in that parking lot and that dataset will not be in this analysis. So this time series, what are they representing? Yeah. My main point about these studies are what is your null hypothesis here that you are testing. What is your expectation. And do you have the data set to test that hypothesis or not? I would say that if the question is did local species, which is changed globally in the last few decades, this dataset is not adequate to answer that question because it's not the random, consistently, consistently sampled data set or uniformly sampled around the world. If this data set is about the impact of a driver like land use change, it's certainly a terrible data set to look at that, because it's not it's not looking at the areas where the land use change and a few areas. When you look at the global scale of the planet locally, it may seem that you know, everything is changing a lot, but globally, you have to really target these places where land use changes, having to to look at the impacts. And so we know from other studies where instead of looking at time series, they look at the number of species these regions in relevance in relation to a reference site. So how many species you have for different groups in the human dominated habitat relative to a reference site that is a native or non managed habitat. And what the database suggests is that for many of the groups, human dominated habitats have slightly fewer species than native habitats. Some human habitats have more species than native habitats. And when you model these, you find we have done a an analysis last year where we compared not only predicts but several of these models where you know how many changes or what is your expected change when certain land use happens. And we modelled and we know from remote sensing how much land use changes has there been. And we reconstruct that. And you can see that over the last century, it seems that there is a decrease of around 2% over and over the years. So this is .02 percent per year, almost zero in local species. So this the first thing is the number is so small. We with many places increasing, some places decreasing. So it's genius that you're trying to measure a very, very small thing. And the second issue is that in reality, not all the models predict that there has been a change in negative trend in local species, for instance. One of the models is predicting even that there may have been an increase for a group like birds in local species richness. And so we we come back to the answer to, to the your question. I don't think we know the answer. I wouldn't bet my a lot of money on it. If I had to bet.

00:18:35: Hahn: So let me summarise. So we're basically seeing looking at local species richness that the trends are very heterogeneous. In some places they go up, and others, they go down and some they stay the same. Um, and if we want to calculate a global average of local species richness, then there's high uncertainty. We don't know whether that would be around zero or much higher or lower. But the next question then is okay, if we acknowledge that these trends are very heterogeneous, why is it even important to know a global average? Because if you want to value it or do something about it, then you would probably have to act on the local level anyway. And then you would have to know how is biodiversity changing in a specific spot? Um, isn't that is that right? Or is it is it important to know whether the the global average of local biodiversity change is that is that important?

00:19:44: Pereira: I think it's an interesting theoretical question. It's an interesting conceptual question. It could also be an interesting question in terms of management. If you deduct that from the experiments showing that ecosystem function can deteriorate when you have a local change in species richness that, well, if local species, which is in most places is going down, because some function is also like primary productivity is also going down. So there is consequences for ecosystem services from trans local species regions. So these are interesting theoretical and let's say applied side to it. But there's so many perils. There's so many problems with the question and with the interpretation that it's it's filled with danger. The both the analysis of the question, trying to answer the question, then trying to use the answer for management again. First, it's usually heterogeneous signal across space, usually heterogeneous signal across stack set. And then if the decrease is happening globally in average it's so small that does it have consequences for ecosystem function. Again the the model mean say 2% per century. That is 0.02% per year. Mm. Okay. What is the consequence of that for ecosystem function. Usually in these experiments where we are seeing exchange ecosystem function, we are knocking like 50% of the species out or something. Although in principle is an interesting theoretical question, an interesting question for management. When you go into the analysis, the rigorous analysis and the rigorous assessment of the implications for policy, it's frightened with danger. Sure.

00:21:46: Hahn: So one, one common thing when you think about this is that there is um, heterogeneity. Um, and the results you get depend on the scale you're looking at. Are you looking global or regional? Where in the world are you looking maybe what time span are you looking at? What metrics are you looking at? Species richness or abundance or ecosystem integrity. Different. Which taxa are you looking at? So it's kind of heterogeneous everywhere. And you can probably find any trend you like, depending on where exactly with what metric you're looking. Still in the in the public. We often talk about biodiversity losses or biodiversity declines, biodiversity crisis. Um, and on the other hand, there's this very neutral term biodiversity change. What do you think would be a good term to use when we when we talk about how biodiversity is changing.

00:22:51: Pereira: I think biodiversity change can be used. But there are two components of biodiversity change. One is biodiversity loss. The species that have disappeared and they are not coming back. And so they are lost forever. That part of biodiversity changes biodiversity loss. And then there is another part of biodiversity change. I call it biodiversity alterations. Some species may increase in abundance. Other species may decrease in abundance. Species richness may increase here, may decrease there in these biodiversity alterations. Are there good or bad? Well, it depends on what kind of consequences have for ecosystems and for ecosystem services. I think you need to assess the importance of those changes and based on on a framework related to some kind of human valuation system in terms of ecosystem services, are we getting more ecosystem services, less ecosystem services. But these biodiversity operations are not positive or negative. So biodiversity loss I think.

00:24:10: Hahn: In the sense of human values.

00:24:13: Pereira: Or human values. So I think we can I think we could all agree or most people would agree that biodiversity loss is negative. Even if you don't talk about human values or the, um, the human, how humans depend on nature from ecosystem services and so on, because these species are to millions of years to evolve and they are disappearing. So there is a sense of loss. Yeah, but if species richness is increasing here and decreasing there, or some species are becoming more abundant and less others becoming less abundant. Is this bad or positive? Well that depends. Um, from a point of view of ecosystem services. Or are you getting more ecosystem services or less ecosystem services?

00:25:07: Hahn: It's not a scientific question, is it?

00:25:09: Pereira: Well, I think it's it's I think the the question is still the scientific question. I, I don't think.

00:25:17: Hahn: Whether it's good or bad.

00:25:19: Pereira: No, no. Uh, let's say, um, if I'm, I'm a coastal community and my livelihood depends on fish that I take from the ocean. If the fish disappear from there, I'll say you can scientifically show that this is bad for this community because they don't have food. Yeah. Okay. So it cannot be self-contained in science. It depends a bit on having an external framework to evaluate it. I cannot say it purely in scientific terms if it's better or good. I need to resort always to some kind of system of values.

00:25:59: Hahn: You have to relate it to human values. For example, the the need for for food.

00:26:04: Pereira: The need.

00:26:04: Hahn: For food. Yeah.

00:26:05: Pereira: For this local community.

00:26:06: Hahn: If we if we agree on those shared values that we need food, then yeah. Then you can call it good or bad.

00:26:12: Pereira: So, so exactly. So it's the framing of the question needs an input from human values. So that's what I am saying is I think although for biodiversity loss species extinctions you could say okay there is a loss. And you can say this is negative almost without having to invoke human values when you go for biodiversity alterations. This, this aspect of biodiversity that is more heterogeneous and well then you need to invoke some kind of human value system to evaluate it.

00:26:46: Hahn: Do you think that we are doing a good job in communicating this well, this heterogeneity, these different types of biodiversity change, whether it's good or bad, differentiating between what we observe and our values?

00:27:06: Pereira: Um, I'm not sure we are doing the job as good as, um, I would like. And part of the thing is that there is a sense of urgency from many people in, in the biodiversity community and in the conservation community that we are losing nature so fast. For instance, we know that the average trend across populations of farmland birds have decreased. They have halved over the last 30 years. We know, For instance, this is maybe easier to communicate in North America. We lost a stunning number. There's been a decrease of 3 billion birds. Individuals. Individuals? Yes. That if that were there, let's say in the populations 40 years ago and they are not there anymore. And so people look at these massive decreases and they say, well, there's a sense of urgency. We need to communicate these numbers. In the case of the birds then you could say, okay, but if some bird species have increased and yes, at the same time the 3 billion birds decreased in North America. This happened in the most common species, and the species were more common in the 70s. Those are the ones that decreased. If you go to the species that were very rare, some of them nearly extinct, they have increased in abundance over the last 40 years. I don't think we communicate that at all because we are so worried about the big number that is the 3 billion number that has decreased that we're not communicating. It's still a mathematical fact that when you sum the populations, because the increase of the rare birds, if you count the total birds, if you have rare birds increasing and common birds decreasing, the total number of birds is still going down. You're still going down. Yeah. You could, even if you want to be controversial, even both in North America and Europe, the species are decreasing. Are open land species, let's say farmland and grassland species. And if you look at, as I said, the species are increasing. In Europe, for instance, some of the forest species have just decreased slightly or even increased slightly. Why is that? Is it because these populations were very, very high? Almost artificially high, these common farming birds, because there was so much farmland in Europe, and now there is some abandonment and some trends towards more forests and more scrubland. And then we have a change in the composition of species. But it doesn't necessarily mean that is bad or you take the view and there is a lot of evidence. Well, this a lot of this is insecticides and insecticides that have killed the prey of these many of the birds. And then they also, you know, affected the food web. And yeah, I would say this is really alarming. And and I think there is some evidence for that. But it's a more complicated question because we tend to focus sometimes on, on the negative things. And, and there is a lot of negatives about what's happening to biodiversity change. And we don't sometimes look at what have been the positive aspects. And I think if I have a my main criticism and going back to your question of communicating this well, is that I think there is too much doom in the biodiversity change and biodiversity conservation and environmental community I've seen in my lifetime. I'm 52 years old. I've seen in my lifetime biodiversity improve in many areas around me, and I've seen species that were extinct, locally extinct, that have come back, and rivers that were dead before coming back to life. And that's because there's been so much positive developments from environmental policy in Europe and in other countries in the world, and there is a lot of hope, and I think there is a lot of hope as we go forward that we can improve the situation in the future.

00:31:48: Hahn: It's interesting because you can support different narratives saying things that are factually correct, but depending on what you focus on, you can support different.

00:31:59: Pereira: Yeah, I.

00:32:00: Hahn: Think narratives and it's kind of our responsibility to find the right balance between, um.

00:32:05: Pereira: I think biodiversity change is such a interesting and complex topic. That is, as many aspects of our human life or our lives, you always need to bring a bit of values to take a stance where where you are. It's not something that is, you know, a theoretical construct and mathematical derivation of good or bad, true or false. You always involve a bit of values because they are so complex topics that you can pick up part of the data and say something, and it can pick up some other part of the data. And even if you take the old data together, the story is more nuanced.

00:32:53: Hahn: Stories inside.

00:32:55: Pereira: There are many different stories inside, and I don't immediately I don't completely agree with with Noam Chomsky in something he said once. And someone asked me, you know, do you use your science to inform your political opinions? And they said, well, politics and it's too complex for science and biodiversity crisis and management of crises. There is a lot of politics. You could almost say, well, it's too complex for science. No, I don't think that's the correct answer. But it tells you a bit of being a bit humble about what we know. What is the science that we have? first? What is the complexity of the problems that we are addressing? So how much of them can be addressed by the science? And then what are all the kind of values. Because politics and its there is also a lot about the values what people value. So we've been interested in developing a new generation of scenarios for the future of biodiversity that we call nature future scenarios. It's been done in collaboration with an intergovernmental platform for biodiversity ecosystem services, the equivalent of the IPCC for biodiversity. And what we are doing there is that we are exploring the range of values of people. Some people want nature for itself, called nature for nature, some people want nature for the benefits bring to people call that nature for society values or nature for society scenarios. And some people say how we cannot separate people in nature. We are one together. Kind of a Indigenous view of the world, native and indigenous people. And this cosmos vision or, you know, idea of cultural landscapes and so on. They call that nature as culture. So even if you look at each of these perspectives, you may have a different analysis of what's happening in different places in the world. Yeah.

00:35:01: Hahn: So basically, I guess we agree that that the facts and the science can inform policies, but it can't dictate policies alone because our values always play a huge role.

00:35:17: Pereira: I must say that I think it's very misplaced, this idea that just follow the science. This has been very popular, for instance, the climate activism and and the idea that, you know, if the politicians should just follow what the science is telling you, we can solve all the problems of of the world. I think there is also this has been also taken up by some of the biodiversity activists and the environmental movement in relation to biodiversity issues. This is just follow. The science is really problematic because of these two issues. One is the complexity of the topics that we're trying to solve and what science tells us. Do you have a complete understanding of what is going on and how to fix the problem? That's the complexity part of the problem. The second part of the problem is do we know what is the problem and how to fix it? Or I will disagree from, let's say, a farmer or from a hunter or from a fisherman. And what is the problem? How to fix it? Because we may have different perspectives about what the problem is. What is the problem? I may have also different perspectives on how effective a certain solution is, because many of these things have trade-offs for different aspects of nature or society. And so then you need to bring the values, and you need to be kind of bring a bit of the democratic decision making in, in between four different stakeholders and come to some democratic decision making. So these two components, one is the values and some kind of democracy and participative process to manage these complex issues. And the other one is this process are so complex that we have to recognise that the science doesn't have all the answers. Sometimes for all of this, we cannot manage all aspects of the world magically for a perfect world for everyone. By science. This is. This is not possible.

00:37:36: Hahn: Okay, so we have to come to an end. Um, could you please very briefly summarise. What would you like to be the take home message for our audience if they remember this conversation in a week from now? What do you want them to remember? Very brief.

00:37:52: Pereira: First, that global biodiversity is is declining, is declining. The global number of species is declining. And we have an extinction crisis. I think this is very solid. Second, that what is happening to biodiversity has two components this loss of species globally. And another component is alterations. And about those alterations they are very ingenious. And um, they vary from place to place, from taxa to taxa. And we, we are still trying to understand what are, are driving those changes and what are the consequences for ecosystem services, and there is very interesting research trying to find out. And third, that, you know, yes, please listen to the science. Please hear what the scientific results are saying about biodiversity change and biodiversity loss, but also understand that we don't have all the answers for how to manage society, and that we always need to incorporate different stakeholders and different opinions in the management of biodiversity and landscapes.

00:39:13: Hahn: Thank you very much. Henrique. Very interesting. Thank you for listening to Inside Biodiversity. Make sure to follow us on LinkedIn, X, and your podcast app. For feedback, ideas or questions, use #InsideBiodiversity or write us an email at podcast@idiv.de.