Siepielski Discusses Evolution, Effect of Climate Change on Animals
Bob Whitby: Hello and welcome to Short Talks From the Hill, a podcast from the University of Arkansas. I’m Bob Whitby, a science writer at the university. Today we’re talking to Adam Siepielski, an assistant professor of biology, who studies biological diversity, natural selection and how species are affected by climate change. Welcome.
Adam Siepielski: Thanks Bob.
BW: So you’ve studied the impact of climate change on diversity and evolution in a variety of species. What are your key findings and why are they important?
AS: Yeah, I would say that, you know, we do think an awful lot about how climate change has affected natural selection and adaptive evolution and species diversity, but the way that I kind of came into thinking about this was really more from sort of a historical perspective, and by that I mean we have a very good understanding that many of the biota that we have today have contended with the effects of climate change throughout their evolutionary histories. In other words, climate change is nothing new but the climate change that organisms experiencing now is, especially in the rate that climates are changing. We were really interested in how historical climate change might affect the diversity of species and how that diversity is maintained or lost, and one of the effects of climate change is the formation of large glaciers. In fact, only about several thousand years ago there were glaciers more than a mile thick a few hundred miles to the north of us, so the communities that are there are much more recently formed and they’re likely to also be regularly disturbed by these sorts of climatic events like large glaciers coming down relative to regions say like in Arkansas that have never experienced that sort of glacial upheaval. And so those disturbances in the north, you know they might prevent species from locally adapting to the environments there including adapting to each other. We are studying damselfly communities, which are like small dragonflies, to understand how this historical climate change may have impacted the ability for species to persist in their lakes, and what these studies are suggesting is that in southern latitudes like in Arkansas, species have interacted with one another in the environment so long that they’re ecologically really distinct from one another, but in northern regions they are not and so basically that the same species may have evolved to be ecologically different in some locations. This really affects their abilities to coexist and all that seems to really be driven by historical climate change. Another project is focused more on how contemporary climate change might affect natural selection, which is the evolutionary process that drives adaptation, and several studies have shown that changes in climate factors like temperature and precipitation affect the natural selection that organisms experience. A really classic example of this is Darwin’s finches. During some years it’s really wet or some years it’s really dry and that changes the selection on the sizes of the birds bills that because that affects their ability to acquire and utilize different seed sizes. And although studies have suggested that those sorts of climate effects might be really important, the extent to which that might be a general phenomena was not known. But it was really important to try to figure this out because if we want to understand if species can adapt to climate change, a critical first step is to understand if climate change can cause selection to change. So myself and a group of international collaborators got together and figured out how to examine a climate might be generally important in shaping selection. To do this we got all the studies of selection we could from the published literature and then used statistical models to ask if changes in selection from one year to the next or from one population to the next, could that be explained by a coincident change in say temperature precipitation. And it turns out that climate, especially precipitation, could explain a great deal of this variable selection. And this is important because by showing that selection was influenced by climate variation, those results really indicate that climate change may be causing widespread alterations in the selection that organisms experience, which might be potentially shifting evolutionary trajectories at a global scale.
BW: You’ve also written about climate tipping points, and that is when changing weather patterns are severe enough to affect how animal species adapt.
AS: It is true that we are seeing more extreme events of changes in precipitation patterns, massive storms, heat waves all seem to be on the increase, and we call them extreme. But you know what makes them extreme from the perspective of affecting the ecological interactions and the ability for species to adapt is just not well understood. An event could be so extreme that no adaptation to it is really possible. So what we wanted to try to understand was what kind of extreme events could actually have a really important role in driving adaptation. We thought extreme events could be important because they might generate these so-called tipping points, and tipping points in general is just sort of the idea that there may be thresholds at the point that once passed generates an awful lot of change in a system even though it only requires sort of a small nudge. So think about a ball balanced on top of a small hill. Let’s say like a flat top so that ball might not be moving very much because it’s just sort of balanced and a slight nudge might move the ball closer to the edge. And then when it’s at that edge even just a little bit more of a nudge might cause it to go off that edge, and when it does it’s unlikely to go back to that former state. So if you think about that in terms of how climate might change and climate driven conditions like changes in climate factors temperature and precipitation which affect the resources that organisms require to survive, it might be that maybe climate varies a little bit from one year to the next and that might indirectly affect resources. So some years that’s really wet or dry or hotter and in other years those changes might be just a little bit more extreme. And those slightly more extreme changes might have major consequences. That’s what we wanted to try to investigate, but not empirically. We did it with math. We were interested in how changes in the environment might cause organisms to adapt to use different resources when resources collapse because of say like a drought event that resource collapse could be a tipping point. To investigate this, we created mathematical models that examine what kinds of resource changes are necessary to cause organisms to adapt to those new conditions, and what we found was that small changes in resources typically have little effect, but just a little bit more of a say of a reduction of a resource, like an extreme drought, might cause an organism to rapidly adapt to those slightly altered conditions and evolve to use different resources. And even when those original resources might kind of come back, so say that drought ended, the rains came and resources came back, the organisms were still stuck using those alternative resources. They passed that tipping point and could not return. Extended droughts or other major changes in resource abundances in nature, some of which are likely driven by climate change, might be having these kinds of effects and we therefore might be seeing the passage of these tipping points occurring.
BW: Biological diversity, how it’s caused, its consequences and how it’s maintained, is one of the main themes in your research. Tell us why that’s important.
AS: There are several reasons why studying biological diversity is important. First I mean it’s really just an absolutely fascinating question. So covering your skin Bob and inside your body are thousands upon thousands of species of bacteria. They’re equally impressive numbers of all different manners of organisms in lakes and ponds that I study, and fields and beaches, there’s just diversity everywhere. How does that all work? I really, really want to try to figure that out. Secondly it is really important for human well-being and health. Food, medicine other resources all come from nature. Ecotourism alone is a multi-billion dollar industry. And you know humans might just consume a lot of a few different species, but all those species in turn depend on other species, so it behooves us to maintain it, and to do that we have to understand what it takes to keep that diversity around, which is really a question that’s sort of the interface between ecology and evolutionary biology where my own studies sort of fall. While we understand a lot about those connections between different species in the environment, there’s just a lot that we don’t know. The interactions between species are really complex because they don’t just occur directly, sometimes the occur indirectly and they’re constantly changing because of changes in climate because of evolutionary change as well and humans. We’re all also embedded in this complexity and we tend to think of ourselves as sort of top of the food chain but that’s not accurate. In fact humans basically sits somewhere between anchovies and pigs in these food webs and there’s plenty of critters out there could eat us. A study had figured that out a couple of years ago. Also it’s the case that you know we are losing lots of diversity and we’re losing that diversity at a really accelerating rate. There are at least five recorded mass extinctions and by all measures we appear to be in the midst of the sixth mass extinction right now as we as we speak. The current rate of extinction of species is estimated somewhere between 1 to 10 times higher than natural background rates. And finally I’d add that you know it’s just aesthetically pleasing to see lots of species mulling about. Go for a hike in the Ozarks or of float down the Buffalo, and one of the reasons we like to do that is this we like seeing organisms out there. Humans are always just drawn to really diverse places like coral reefs and tropical rainforests, but diversity is everywhere you don’t have to go those exotic locations. Where we are in the Ozarks is just a fantastically diverse place, it’s really cool.
BW: You were a co-author on a 2015 paper about animal mass mortality events MMEs as you call them. That’s when a large number of species die at the same time and it’s not immediately clear why. That paper got a lot of attention and one of the key findings was it in it was that you had seen more of these events since the 1940s. Why is that?
AS: I thought of this idea actually listening a story on NPR. I was a postdoc at the time and I just heard the story about all these sardines involved in this shoaling event in a really shallow water, I think it was in a bay in San Francisco, and there were so many of these individuals in this little bay that they basically draw down the oxygen and they all died. It was just millions upon millions of fish. There were all these crazy pictures on NPR’s website. After hearing that story I just became really interested in whether or not these were a common phenomena and sort of what we had understood or not understood about these so-called mass mortality events. So I got a number of researchers together to try to figure this out. It’s kind of interesting that Arkansas was actually the epicenter of these events just a few years back. It was December 31st 2010 when thousands of red-winged blackbirds died all of a sudden and a few weeks prior to that a bunch of fish had died in the Arkansas River and it garnered just a huge amount media attention at the time. But from the scientific perspective we really don’t understand whether or not those events were rare, whether they were changing in frequency, you know nothing like that. And one of the findings from that research was that it did appear to be the case that mass mortality events were increasing. As you had noted though one issue was that it might just be that it’s just greater awareness so people heard in 2010 these mass mortality events and so they might just be more likely to start reporting that sort of thing. It was really difficult to try to tease apart whether or not this was a real phenomena, were mass mortality events really becoming more common or whether or not it was just kind of an epidemic of awareness, people were just paying more attention to that. And there’s there no really no simple way to disentangle, that there’s nothing statistically you can do, there’s no fancy mathematical models. We’re just stuck sort of, but they very well may be increasing in frequency and that might have some important consequences. The major underlying causes appear to be starvation and disease. Those are just appear to be increasing in frequency and appears to be causing more and more of these mass mortality events. But one of the things that is less likely to be biased by that increased reporting is that for some groups of organisms, especially fish and birds, that magnitude that is the number of individuals that were dying in each of those mass mortality events has been increasing through time. And some of these mass mortality events are just huge. These might be a billion individuals or 7 million tons of dead biomass, 7 million tons of fish dying in a lake in just one event it was really kind of a morbid project for sure but one of the things that we don’t know was what the consequences of these mass mortality events might be for ecosystems. I mean 7 million tons of dead fish accumulating in a lake that humans might use could have some obvious consequences for human health, both directly because of having a bunch of decaying fish but also just the consequences of removing a really important consumer. Those fish are controlling other species in those systems and when all of a sudden you wipe them out that’s likely to have important consequences which might sort of affect the balance in those ecosystems. And so we’re continuing to try to understand more about these mass mortality events and we’re using several different approaches. The first of those is to develop theoretical models just to try to get a sense of what might happen during one of these mass mortality events. And secondly we’re busy trying to secure funds to actually experimentally cause mass mortality events on a smaller scale. That might seem somewhat alarming, but we think we can do it on a small scale to try to recreate what might happen. This would be done in small so-called mesocosms which we’re basically just like little plastic containers about the size of a kiddie pool and we can learn a lot from investigating these systems from such a small scale experiment. But we really do need experiments to try to understand what’s going on and so because these events might be increasing, and they certainly appear to be increasing in magnitude, it’s really important to try to understand their consequences on the environment.
BW: Well it’s fascinating, if slightly morbid research, and we thank you for joining us today.
AS: Yeah, thank you.
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