Short Wave - Climate Change Stresses Out These Chipmunks. Why Are Their Cousins So Chill?

Episode Date: December 23, 2022

Kwasi Wrensford describes the subjects of his research as "elfin": skittish little squirrel-cousins with angular faces, pointy ears and narrow, furry tails. He studies two species in particular: the Alpine chipmunk and the Lodgepole chipmunk. As the climate warms, these two chipmunks have developed different ways of coping. The Alpine chipmunk has climbed higher, in search of cooler habitat, while the Lodgepole chipmunk continues to thrive in its historic habitat. On this episode, Kwasi explains to Emily Kwong how these squirrelly critters typify two important evolutionary strategies, and why they could shed light on what's in store for other creatures all over the globe. See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Quasi Runsford studies chipmunks, and they keep him on his toes. I would describe them as elfin, like elf-looking. They have these really angular faces and the pointy ears. They're very zippy. They're small and they're fast. So it's like the two things you don't want for something you have to spend a lot of time looking for and observing. And they're full of personality.

something Quasi's seen firsthand over summers of field research observing their every move. I do my work up in the Sierra Nevada Mountains of California. You'll see a chipmunk. It'll kind of be posted up on a rock and it'll just be really still. And then it'll just take off like a rocket. To be more specific, Quasi studies two chipmunks in the Sierra Nevada Mountains, the lodgepole chipmunk and the alpine chipmunk. They eat similar food, act in similar ways. But between these two species, he's observed one clear.

difference. And so we have these two chipmunks, very similar habitats, very closely related, similar ecologies, but very different responses to climate change. What makes an animal more likely to be resilient to climate change versus sensitive to climate change? Today on the show, with the tale of two divergent chipmunks, could teach us about how other animals may fare in a changing climate. I'm Emily Kwong, and you're listening to Shortwave, the Daily Science podcast from NPR. Quasi Rensford is a PhD candidate at the University of California, Berkeley, in the Department of Integrative Biology. And he's super interested in how animals are responding to and coping with climate change, specifically two species of closely related chipmunks. One is the alpine chipmunk and one is the lodgepole chipmunk.

And these species both live in sort of the higher elevation levels in the Ceras. So the lodgepole lives between sort of seven. thousand to 10, 11,000 feet in elevation. And the alpine chipmunk lives between 9,000 and 13,000 feet of elevation. So they're sharing habitat and they're coexisting in similar environments. But what we've been able to see over the past 100 years is that the alpine chipmunk, its range has been shrinking over the past 100 years, we think due to climate change and moving further up in elevation, that pattern we've observed in a lot of other species in response to warming temperatures. However, the lodgepole chip bunk has not shown that same upward movement in its range.

In fact, it still can be found in the majority of its historic range. And so that sets up the question then. What is different about these two species that makes one sensitive and one resilient to climate change? Do you know when these two species diverged? Right. So our best guess for when all of this diversification took place is during the last periods of glacial maxima. of the chipmunks were treated, and that time they spent cut off from other chipmunk populations, allowed them to diversify and diverge into new species. And then when the glaciers receded,

they kind of all came back into contact, but diverge far enough that they don't really reproduce anymore. And so we're thinking all of this, most of the chipmunk species are at least a couple million years old. We're talking about a really specific ecosystem here, which is the alpine. Can you describe what that is and the challenges that? animals who live in the alpine face, especially as the climate warms. Yeah, alpine ecosystems are a particularly challenging one for animals to live in. First of all, there's a lot less oxygen, right? It's also usually cooler and drier.

Winters are a lot longer in these high-elevation habitats. Therefore, the growing season, the time of year when plants are out, that's a much narrow window of time. And so for a chipmunk, it maybe finishes its hibernation around April or so. And then it has until October to do everything it needs for the year. So find a mate, get enough food for its offspring, and to have enough energy and fat reserves for the winter. It has to do all of that between April and October. And so what we're seeing with climate change in alpine environments, and particularly in the Cierras, is that as the temperature is warming, the growing season is getting longer, which intuitively might seem like a good thing, and in some ways it is,

in that the animals now have more time to do all those things they need to do versus in the colder times. However, these animals are adapted to that time frame, and so shifts in that timing that animals aren't prepared to cope for can have drastic effects, even if it technically gives them more time to do what they need to do. And so it's throwing their whole calendar out of whack. Yeah, the timing, it sounds like, really matters for these chipmunks. So in looking at these two species and figuring out why they diverged and why their ranges are so different, you had to actually catch chipmunks. How did you do that? Right. So we do that using these really simple live traps. We kind of pick spots that we know or have a good suspicion that there's chipmunk activity. And then we set up these traps, these metal box traps we call Sherman traps. And they're very simple. There's a little metal box with a trap door. And then we bait them with something chipmunks find delicious, usually peanut butter, bird seed or oats or something like that. Peanut butter would work on me if I were a chipmunk. I would just walk right into that trap.

Yeah, everything loves peanut butter. And so the chipmunks will go in, but also other species of ground squirrels. I've had bears trample my traps because they just smelled like peanut butter. They don't even have peanut butter in them anymore, but they smelled like peanut butter. Those Sierra Nevada bears. Okay, so you're setting these traps in this grid pattern and checking them. And every so often you get a chipmunk. Tell us a little bit about this portable,

arena that you put your chipmunks in to like evaluate their behavior. What's going on there? Yeah. So it's my take on a pretty standard test of anxiety, boldness behavior that's used in a lot of animals called the open field test. And basically all you're doing is you're taking an animal, letting it acclimate for a bit, and then placing it in a new, potentially scary because it's not familiar space to that animal. And then you observe its behavior over that period of time. Is it zipping around trying to explore every nook and cranny? Is it huddled in a corner in fear for its life?

Those are differences that can tell you a lot, potentially, about how these animals respond to changes in their own environment. And what did you see? And what I've seen so far is that our alpine chipmunk, our high elevation species, whose range has been shrinking over the past years due climate change. It tends to be, A, a lot less active. So once it actually enters in the arena, it's a lot less mobile. It's a lot less busy than the lodgepole chipmunk. And it takes a lot longer for them to enter the arena. Interesting.

So these two chipmunks, they're not the same at all. At least they don't behave the same way in the arena. I understand you also compare data on their stress hormone levels. How does that work? So for hormonal data, the way we get that is through collecting fecal samples from the individuals that we capture and measure and mark and everything. So you feed them peanut butter and then you steal their poop. Exactly.

To study it. Yeah. I love science. This is the most glamorous part of my job. And so with hormones, you can get hormone levels from a lot of different sources. What feces tell you instead of blood is that they give you a much more sort of average over time picture of the hormone levels than a blood drop would. And so that's a lot more of a relevant measure for thinking. about environmental stressors and things like that.

And what differences did you see between the two chipmunks? Right. And so we see two major differences. One is that we see that the Alpine chipmunks, our higher elevation species, has much higher, like, spikes in stress levels. So we did these things called handling tests, which is very simply you take a fecal sample on the time series, and then you handle them, and then you take fecal samples after that, and then you see if there's a spike in the hormone levels in response to that handling stress. And what we see is that the alpines, you see it really sharp spike in the hormones after that handling test. On the lodge poles, you barely see anything.

They're cool as cucumbers. Yeah, they are chilling. And then the other difference that we see is that when the average highest daily temperature is higher, we see elevated baseline stress levels in our alpine chipmunks that we don't see, and we don't see that pattern in the lodgepole chipmunks. These are such interesting patterns you found that there's one chipmunk that has a lower baseline stress level, is totally down to enter the arena and poke around. The others, not so much. This is more hesitant, has higher baseline stress.

What do you think these differences suggest about how these chipmunks are living? That is the $100 million question of my research. The picture that's starting to form with these two species is the alpine chipmunk, the one that is his range has been shrieking. who seems to have these higher stress levels when exposed to unfamiliar, potentially risky situations, is showing all the signs of an ecological specialist. It has adapted and evolved into this very narrow, but very optimized strategy for surviving in these high-election habitats.

While our lodgepulled shipmunk are much more easygoing, are less stressed, our bolder, more active individual when exposed to newer or riskier situations, it displays all the characteristics of an ecological generalist. What big picture lessons do you take away from this tale of these two chipmunks? Yeah. I think when we talk about climate, a lot of things are going to struggle and potentially go extinct in response to climate change. The more difficult question that we have to face in animal ecology is which species are the ones that are going to go first, which are the ones that are most vulnerable. And what this chipmunk work seems to tell us is that species that are more specialized that have a narrower sort of toolkit in responding to their environment, even though that they're very good at using those tools, those might be at much greater risk in the short term from climate change than those species that have a more generalized toolkit that have a lot more strategies available to them.

And while there are animals that will survive and animals that will adapt and thrive as animals have done for millions of years, Those animals that are doing well are going to occupy a lot narrower range of diversity. There's going to be a lot of life around. It's just going to look really different. And part of it gives me solace, too, and that there are animals out there who are in other species of organisms or living things that are able to flexibly adapt and cope and tough it out. And it kind of reminds me that if you want to be resilient to the unpredictable,

you need to have a broad and diverse twist. kid. Absolutely. Quasi, it was very awesome to talk with you about your research and about chipmunks. Thanks so much for coming on the show. Oh, thank you for having me. This episode was produced by Burley McCoy, edited by Gabriel Spitzer, and fact-checked by Uby Levine.

The audio engineer was Josh Newell. Brendan Crump is our podcast coordinator. Beth Donovan is our programming senior director, and Anya Grundman is our senior vice president of programming. I'm Emily Kwong. Thanks for listening to Shortwe. The Daily Science Podcast from NPR.