How Can We Make Sense of the Biodiversity Conservation Paradox?

: Hahn: Welcome to the very first review episode of 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 impact Unit at iDiv. In this episode there is no new guest. Instead, we will review past episodes that address global and local biodiversity change. One motivation why I initiated this podcast was to challenge dominant narratives about biodiversity change. I often felt that the media portrays biodiversity and biodiversity change too simplistically, and fails to appreciate the complexity of the changes that our natural world is experiencing. So I dedicated the first episodes to the so-called Biodiversity Conservation Paradox. For episode one, I invited Maria de Ornelas. Maria was one of the first researchers to discover in her data what another researcher, Mark Vellend, coined the Biodiversity Conservation Paradox. Listen to what Maria said in the podcast.

00:01:10: Dornelas: About ten years ago, we started assembling a database of biodiversity time series called Biotime, and then we started extracting trends from that database. And much to our surprise, when we first started doing it, I very much thought that I was going to be talking about losing mammals faster than we're losing plants or something to that. Um, similar to that. And instead, what we found is that the biodiversity, temporal trends in biodiversity are much more complex than I was anticipating. And there's rather than finding systematic loss everywhere, we see mixed trends with some increases, some decreases, and some remarkably stable trends in the numbers of species that we see in any one place. It took us maybe two years to actually trust those results. I'm publishing them, and when they were published, they were fairly controversial. Um, but, um, I would say that they've held pretty well, and it's now been ten years and I don't think very willing to, uh, be persuaded otherwise, but I don't think I, I don't think anyone has shown that we were wrong in that pattern. So it's just turned out to be much more variable than we thought it was going to be, in terms of the numbers of species that we see in any one place. But at the same time, what we also found is that there is really, uh, extraordinary change in the identities of the species that we find in one in any one place. And so, like one of my hobby horses at the moment, is that I really think that we should be talking about biodiversity change rather than just talking about biodiversity loss.

00:03:01: Hahn: Your work is cited a lot in the context of what is called the Biodiversity Conservation Paradox. Can you explain to us what that paradox is and why it's paradoxical? What is paradoxical about it?

00:03:18: Dornelas: Well, the paradox comes from like the realisation that humans have undoubtedly changed the planet in really substantial ways. And we know that a lot of what we do to this planet, from climate change and land use change and different extraction activities, is typically not great for biodiversity, quite frankly. And so how do you then reconcile that knowledge with also the observation that at least since we started seriously monitoring biodiversity, we don't detect declines everywhere. I'm also puzzled by this. I think I don't have an answer to. And I think from a purely scientific point of view, then that's kind of cool, because it means there's more questions to ask and and more things to understand.

00:04:09: Hahn: So Maria Dornelas found that biodiversity is not declining everywhere. She also said that her findings caused controversy. So I wondered how surprising were her findings for her colleagues. So an episode for I asked this question to Henrique Pereira. Henrik explained why mixed trends at local scales do not contradict species extinctions at the global scale.

00:04:34: Pereira: 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 disappear, but there is also some species that show up, particularly for very mobile species. There's some species that colonise and you can have a situation. It is perfectly possible to have a situation where the number of species globally declines. But if I count the number of species in my backyard and in all backyards of everyone, you can have an increase in the generalist species that spread and a decrease in the narrower species and and the narrow range species in the specialist species. And you could have this kind of situation where locally the species richness can increase and global species richness decreases. But it's not only about that. It's also about this very heterogeneous change. So if I say, okay, we have a few species that have disappeared over the last 500 years, okay. But did I notice that in my, in my, in my place or in my backyard? Well, this species was never in my backyard, so maybe I have not noticed it. 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.

00:06:27: Hahn: So perhaps it wasn't that surprising to find those contrasting trends in different locations. In episode three, I asked Jonathan Chase for his opinion. Interestingly, he challenged even the idea that higher biodiversity is always good. Take a listen.

00:06:44: Chase: Yeah, I mean, this is interesting because I was actually a reviewer. You know, in peer review, these papers often get reviewed before they're published. And I was one of the reviewers on on both of those papers. And I really had a mixed feelings because on the one hand, it was surprising we had built an entire set of ideas based on the idea that we're in a biodiversity crisis. And we didn't again, really think about the scale problem. And so if species are going extinct globally, they're going extinct locally. And we just felt like there should be some proportional loss across those scales. And that really even set up some of the the current research programs, like the role of biodiversity and ecosystem functions and services, those are predicated on the idea that local biodiversity is declining. It just made sense. But actually from an ecological perspective, if you forget about conservation and you just think about basic ideas and biodiversity maintenance, things like the theory of island biogeography, which we've had for 40 years, these theories predict that we shouldn't expect a lot of change at local scales. We'll see a lot of turnover. We'll see shifts in species. Which species are.

00:07:57: Hahn: So sorry to interrupt. So turnover means that there are different species than there used to be.

00:08:03: Chase: And in this particular case, turnover means through time that there may be one species in the in a few years, but then it's replaced by a different species. Yeah. And when we think about, especially in the context of, of humans in the Anthropocene, we know humans are actually favouring this concept of biodiversity in many places when we go to, um, a to start, when we chop down an old growth forest, we get more species. You know, the the idea of local diversity going down actually doesn't make sense when we think about basic ecological theory. Humans are changing the environment that there's no doubt about that. But biodiversity doesn't have to go down. And we've created this idea that biodiversity is good. And when biodiversity goes down, it's bad. And from an ecological perspective, that doesn't make sense. And I think that we kind of backed ourselves into a corner by creating biodiversity as this, this, this entity that that emphasises good. You can have huge levels of biodiversity and habitats that are strongly degraded by people.

00:09:16: Hahn: So several podcast guests confirmed that the findings of Maria Dornelas and others were not that surprising. Not that paradoxical. However, as Maria mentioned, the studies did spark heated controversy. Andy Gonzalez was one of the study's critics, so I invited him to be a guest on episode two of Inside Biodiversity. Here is an excerpt from his critique.

00:09:43: Gonzalez: I don't think anyone was surprised with the finding that in some locations, biodiversity, maybe some measure of biodiversity, in this case, species richness is going up and in other places it's going down. That's no surprise to a community ecologist. What was surprising was the conclusion that this was representative of the global system. And so what the papers that I were involved that were criticising or critiquing those papers was that, hey, we need to recognise that the data sets that are available in the literature that we can use to do the monitor analysis, have certain geographic biases. We sample species in certain locations on the planet. And in fact, the surface area of all those locations is much less than 5% of the Earth's surface. So we don't have a representative, geographically representative distribution of data. Nor do we have a taxonomically representative data. So we're not looking across all taxa or even something that's representative of the tree of life, which is important. And then there are other biases for the sake of time. I'm not going to go into all those biases, but those are the two key ones. And and a secondary point. There was an immediate association with the role of humans and how land use change, climate change, pollution. Invasive species may or may not result in a net change locally. And to answer that requires building data sets that have also collected the causal drivers, the things that drive change in species richness.

00:11:18: Hahn: Here is my takeaway from the discussion on the Biodiversity Conservation Paradox. Species have gone extinct on a global scale and those species will never return. Although we may discuss de-extinction on inside biodiversity in the future, in any case, global extinctions do not necessarily mean that local species richness decreases everywhere. The metric of local species richness does not fully capture what's going on. The number of species may not change, but the composition of species does change almost Everywhere which species is present and how many individuals. We will talk about abundance and biomass later. Also, what happens at local scales is very heterogeneous. In some places species richness decreases, while in others it increases. Or maybe it remains stable. This is due to natural variability on the one hand, but also the impacts by humans vary considerably. One widely discussed driver that is basically at play everywhere on Earth is climate change. I dedicated episode ten to climate change and I spoke with Miguel Araújo about it.

00:12:34: Araújo: This clearly a a trend towards favouring warm tolerating species and species that are cold adapted, suffering more so species. For example, in northern Scandinavia and in tops of mountains, they tend to be shifting further north and further further in altitude, and then having to compete with species coming from below or from the south. Right. Uh, so those are clearly, um, becoming refuge species that were already refuge species because we live in, in a fairly warm times. We are in an interglacial that is a period between glacial periods. So warm period. So those species that were adapted to colder were already cornered in the top of the mountains and in, in the higher latitudes. And they are now there's a driver pushing them further north and further furthering altitude. So those, you know, if you like to use your words, they would become losers. They are losers in the current, in the current scheme of things. And then the species that tolerate warmth, they will they will expand. They are already expanding.

00:13:40: Hahn: That also means that we have some areas, maybe in general, the colder areas where the number of species might actually increase.

00:13:49: Araújo: Yes, yes.

00:13:50: Hahn: In others, more in the warmer regions where we can expect or already observe that species, the the species richness or the number of species is decreasing.

00:14:00: Araújo: Yes, for two reasons. One reason is that the pool, the pool of species on Earth that tolerate warmth, is greater than the pool on Earth that tolerates cold. Um, so there's more species, um, available to colonise, uh, areas that become suitable because they become warmer than colder species on Earth. So this imbalance will cause increase of species richness locally because there's more species coming in, uh, than ones going out. But also, uh, productivity will increase. Warmer temperatures associated with, uh, greater amounts of water availability, uh, will increase the quantity of energy available for consumption. And if energy available for consumption increases the immediate reaction. The immediate response is an increase in the number of organisms that can that can exploit, and it can be different, more individuals of the same species, or it can be more species.

00:14:56: Hahn: Again, biodiversity change is complex and the drivers such as climate change do not necessarily cause losses. Only are more species in a given place necessarily a good thing? I think it depends on what we value. For example, the island of Madeira now has more plant species than ever before because of humans. Is that a good thing? I discussed this topic in episode six and seven with Martin Winter and Emma Marris, and I recommend you give them a listen, but I won't be playing any clips from those episodes in this one. Until now, we have only discussed species richness, which is the number of species in a given area. Also, until here, we have discussed biodiversity change in general without looking at specific species or taxonomic groups. In episode 13, I talked to Roel van Klink about local insect changes. He focussed on abundance and biomass, which are different metrics than species richness, but he did stress that they are related.

00:16:01: van Klink: I think by now it's well-established that insects in most places are not doing well. They are declining. There's some controversy about how much the decline is. There are some people who believe it's absolutely catastrophic, and we're looking at 7,080% decline since the 90s. My own research of putting all these data together shows it's more in the realm of 30 to 40% since the 90s, which is still a lot. It's but it's not 90%. Um, so and I fear that that's also a little bit ideologically driven debate of.

00:16:41: Hahn: We're not talking about like, like we mentioned before, we're not talking about number of species, but abundance.

00:16:47: van Klink: Total total abundance. Yeah. Of total abundance or biomass. Just the sheer number of insects and the number of species has to be related to that. That is mathematically almost impossible not to be related. And we also tested that a bit in one of our papers. So the amount of decline that is maybe where there is a little bit of controversy and then there will be maybe a person here or there that just believes that there's no decline at all. But I've had haven't heard that argument in ages.

00:17:21: Hahn: After insects came mammals. In episode 15, I spoke with Carlo Rondinini about global mammal trends, and I found it fascinating to learn how different metrics can tell very different stories. I recently came across a number that I found quite astonishing that if you look at the biomass of mammals worldwide, the global share of wild mammals is only 5%, meaning that 95% of global biomass is humans and livestock and pets. And I also found another estimate that says wild biomass is estimated to have declined since the rise of humans by 85%. So huge declines when we look at at biomass. And what I find interesting is that we don't see it in species extinctions. You mentioned that less than 2% of mammal species have been extirpated since 1500. We already talked about that. It's a complex picture, but having such different stories that you see when you look at different metrics like biomass on the one hand, maybe population sizes and then species that I have become globally extinct are less than 2%. What does that tell us? How do we make sense of that?

00:18:51: Rondinini: This is an important technical question. We see the same, for example, in indices. And we know very well that in the seas many of the species will likely not go extinct at all in the near future, but have been so depleted that fishermen don't go for for those pieces anymore. Usually, the shape of the decline of species in terms of population size is not linear, but it's a negative exponential. So if the decline is at a constant rate, you expect big declines when the population is big and small declines when the population is small, never approaching extinction. What brings extinction, then, is a stochastic process, something that is actually completely random and happens in very small populations where whatever random external factor, environmental factor, or some change in some loss of a specific level of a gene, and then in the genome of the population brings a decline. Or it extinction may take a long time after the population has actually been depleted. Or some say, even if I don't particularly like the term Afghan functionally extinct. So we tend to have many functionally extinct species that might survive for centuries or even millennia just because of chance.

00:20:23: Hahn: Interestingly, when we talk about global plant biomass, the picture is very different from mammal biomass. Satellite images show that the Earth is becoming greener. This phenomenon is called global greening, so it means green biomass is increasing. In episode 16, I asked Helge Bruelheide and Ute Jandt whether global greening translates also to more plant diversity.

00:20:49: Bruelheide: The best and first answer is it's a matter of scale. So it depends whether we look at the total planet where we can say that we are losing plants. So the global extinction of plant species is estimated to be around 600 700 plants out of 400,000. So it's not it's not that much globally. And on the other hand, we also have the so-called biodiversity paradox. Yeah. So we are observing the change on vegetation and wood. And I we are doing this with many, many colleagues on, on certain plots, on areas that say of ten by 10 or 2 by two metre squared. And what we observe is that very often species richness doesn't change. You go there and we might find exactly 25 species on ten metre squared, as we did as I did 30 years ago. The interesting point is that the species are different now. Yeah. So it's not only the species number, but we find certain species that have increased. Very often the same species increased in very different plots while we are losing species that are specific to some habitats. And this can be summarised under the term homogenisation. The word becomes more similar. That means on this scale we are not losing plant diversity, but we are losing more different habitat types. So at the globe we're losing at the local scale, we're not that much losing. And interesting is the scale in between. So when you go to hectares or to regions like, um, the council here of colour or a federal state in Germany, whatever, then you find there is a lot of change going on. We are losing a lot of Species locally and regionally because the habitats have simply gone. So in principle, the answer is are we losing plant species. Depends on the scale, but it certainly happens in particular at these intermediate scales.

00:23:04: Jandt: We have several approaches to to find out about these changes at the local scale, which we do in vegetation plots. As Helga said, we see that on this local scale, the specialist species for specialists, for specific habitats, they are getting more rare. So they are lost in some plots, not in all the plots, but in some. And we get some generalist species which occur in more and more plots, so they get more dominant. And they we have these homogenisation effects in nearly all habitats.

00:23:41: Hahn: Once again, when discussing biodiversity trends, the metric matters. Species richness is not the same as biomass, and the scale matters. Local trends do not directly translate to global trends and vice versa. Also, the time span matters, and to make it more complex, the taxonomic group or even the species matters to plant trends are different from mammal trends, and mammal trends are different from insect trends. We will cover more taxonomic groups in future episodes. For instance, reptiles will be next. So I hope you agree that biodiversity change is not a simplistic story of just losses, and it is not a simplistic story of good or bad. There are losses and there are gains, and you cannot understand biodiversity change without considering nuances. I hope this podcast helps make those nuances visible and understandable. I want to end this special episode on a positive note. Biodiversity change has many gloomy stories to tell. There are stories of ecosystem destruction, stories of species extinction, species that will never return. But there are also hopeful stories. For example, there are quite a few mammal species in Europe that are making a comeback, and I discussed this with Carlo Rondinini. After that, I will play a short excerpt from episode 11 with Katrin Böhning-Gaese. And finally another excerpt from episode four with Henrique Pereira. Are there more mammal species expanding in Europe then decreasing?

00:25:19: Rondinini: That is probably the case for Europe overall. Um, we have, uh, some. Some of them are conservation successes, like the Iberian lynx that were a target of specific conservation actions, reintroductions, management of of rabbits that are the the most important prey for the for for that species and others have been re expanding in Europe for a variety of reasons. Like beavers that have been reintroduced somehow, officially, somehow unofficially in different countries, but certainly are expanding. We had otters expanding, probably because of the slightly different reason from the others, but again linked to a reduction of pressures that was brought by by European regulations on river quality, water quality, reduction of of pollutants. And they naturally re expanded. So let's say that the general rule is that whenever we we leave space for mammals, they they come back.

00:26:29: Böhning-Gaese: There's also scientific evidence that nature conservation is working, that there's meta analysis, analysis showing that two thirds of the nature conservation management measures actually worked. We see that since 1992. That was the big summit in Rio de Janeiro, where the CBD, the Convention on Biological Diversity, was founded. We have actually lost 15 species of mammals and birds. However, we have also saved between 28 and 48 species of birds and mammals, three to 2 to 3 times the number of species so that we can actually save biodiversity. We can restore ecosystems so we can tell positive narratives.

00:27:17: Pereira: We tend to focus sometimes on on the negative things. 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 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 becoming 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.

00:28:11: Hahn: We will discuss environmental policy further in future episodes. I hope you enjoyed this review of Inside Biodiversity episodes, focusing on Biodiversity Change and the Biodiversity Conservation Paradox. I hope it helps you make sense of the complexities we deal with when trying to better understand how the living world is actually changing. I welcome your feedback, so please write an email or leave a note on social media. Thanks for listening. And until next time on Inside Biodiversity.