E4: The reshuffling of life on Earth

Madison Goldberg: Science happens in a lot of places. Sometimes it’s in a lab. Sometimes it’s at a computer screen. And sometimes it happens on the side of a mountain in New Hampshire.

Here, the landscape around you is shaped by elevation. When I visited with a pair of researchers, the air got colder as we climbed. Snow piled up, and there were more spruce and fir trees. It felt like we were moving through multiple worlds as we hiked up the path.

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Alexej Sirén: This is where we get our ideas from, right? This is where you develop these really deep hypotheses, because it's the first part of the scientific method, is to observe, right?

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MG: Alexej Sirén works at the University of New Hampshire, studying how things like climate change and habitat change affect wildlife—including many of the animals who live up here, in the cold of New England’s White Mountains.

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Toni Lyn Morelli: These species go all the way up into Alaska. These are these cold-adapted, snow-adapted species.

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MG: That’s Toni Lyn Morelli, of the U.S. Geological Survey and the University of Massachusetts Amherst. She also studies how wildlife is responding to climate change—and how we can conserve species in the face of it. And here’s a big question that’s on both ecologists’ minds: how is a warming world reshaping where species live?

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TLM: We're just particularly worried because the marten and the snowshoe hare and the red squirrels, they're all species that—

[Boreal chickadee calls.]

AS: And the boreal chickadee.

TLM: And the boreal chickadee. These are all species that are dependent on it being snowy in the winter. So as a result, we think, okay, well, where's that chickadee going to go? Like, is it going to stick around here or is it going to, in, you know, twenty years, have to have gone somewhere else?

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MG: Welcome to Ask MIT Climate. I’m Madison Goldberg. Today, we’re exploring what a warming world means for our fellow species here on Earth—and, specifically, where on the planet they can survive and thrive.

TLM: Species are trying to keep up with their temperature that they evolved in, that they are most comfortable in, and that they will survive and reproduce best in. And so they're starting to move around.

And it would be great if we could predict exactly where they're going to go. And we're getting better at it. But it seems pretty complicated, because ecosystems and species are complicated by all of their different needs and behaviors and traits.

MG: But let’s start here. What does it actually mean for a species to move? It’s not like all the boreal chickadees turn to each other and say, “Okay, guys, time to pack it up and head somewhere colder.”

To help us imagine how it might happen, Dr. Morelli gives the example of a tree species in North America.

TLM: When it spreads its seeds, those seeds go far and wide, often, if they're wind-dispersed.

MG: The area of the world where this tree lives is called its “range.” We’re in the northern hemisphere, so broadly speaking, the northern part of the range is colder, and the southern part is warmer. And the planet as a whole is warming up with climate change.

Okay, so these seeds get carried off by the wind.

TLM: Now, maybe, a hundred years ago, they would have been dispersed into an area to the north where it was just too cold for that seed to set. Now, that area might be warmer. And so now when the seed falls, it doesn't just die off, it actually can sprout into a new, eventually, adult tree.

We can also imagine a contraction on the warmer edge of the range. So that's the southern edge. And there we might see a totally different mechanism, that could be individuals dying from heat waves or drought. They could be not able to reproduce there, so you just, eventually, over time, see that nobody's growing. There's no new baby trees.

MG: We could also picture this tree on a big mountain, where temperatures broadly drop the higher you go. And so you can make a first, rough guess at how you’d expect species to move as the planet warms.

TLM: The coarsest, simplest predictions for the ways that species will respond to climate change by shifting their ranges is upslope, poleward, and deeper in the water, whether that's the ocean or a lake.

MG: So, what are we seeing?

Well, Dr. Morelli and her colleagues sifted through tons of scientific papers to gather tens of thousands of recorded observations. Some looked at whether the warm or cool edge of a species’ range had moved over time. Others looked at whether there had been a change in “abundance”—that’s the number of individuals in a given area—in part of a species’ range.

TLM: And we found about fifty percent, less than fifty percent, have met our simple predictions.

MG: The other half of the observations didn’t line up that way—like, maybe they showed a species moving toward the equator, or not moving at all.

So, the question is: why aren’t we seeing everyone move in the same, predicted directions?

TLM: There's two layers here. It's like, is it actually happening? And then can we record it? We might have trouble recording it if we're looking at the wrong season or we're looking at the wrong life stage.

MG: This is hard research to do. Like, it’s tough to be sure you’re mapping the true boundaries of a species’ range, or that a shift you’re seeing isn’t just noise.

But our simple predictions might also sometimes be wrong. For example, maybe a species doesn’t actually need to move—or, at least, not yet.

TLM: So, in a way, maybe some of this is good news, in that maybe individuals are behaviorally or even evolutionarily able to adapt in place. It may be, though, that we are now going to see reduced reproduction or some higher mortality or something as a result of them staying in place.

MG: Or maybe a species can’t move, or can’t move very fast. Maybe they live in the woods, but deforestation has made the landscape too patchy for them to get very far.

Also, we’ve been thinking about how species will respond to temperature changes. But in our warming world, there’s a lot more than temperature that’s getting shaken up.

TLM: So maybe they're responding to precipitation, which isn't moving just as simple as poleward or upslope. You can also imagine that, well, species don't just respond to climate, they respond to other species and habitat and their food sources. And those could be driving in a different direction.

MG: Which is my cue to introduce you to the American red squirrel.

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TLM: They’re sort of like the noisy neighbor of the forest. And so if you have the luck to be walking through the White Mountain National Forest, you are likely to hear a red squirrel chatter at you because they want you to know they're there and they've seen you, and so you shouldn't try anything fishy.

AS: Or you may have bumped one of their neighbors and that neighbor is going away from you, and that triggers the other one to be like, get out of my territory. How many times?

TLM: How many times?

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MG: Here’s what a red squirrel sounds like, by the way.

[Red squirrel calls.]

MG: And it turns out those calls can be useful for keeping tabs on where red squirrels are living. Dr. Morelli and Dr. Sirén, along with their fellow researchers, have used them to ask: Are red squirrels here moving in line with the changing temperature? Or—are they doing something else?

Because here’s the thing. Dr. Morelli says that the red squirrel’s habitat has also been changing here. After a period of dieback, the conifer trees the squirrels rely on have been regrowing.

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TLM: They're actually filling in downslope because they’re recovering from these other stressors.

So it turns out we think the red squirrels are actually tracking their habitat and not their temperature. For now. A researcher in one hundred years might find a different pattern.

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MG: Other animals in this region also show how complex these questions can be. Dr. Sirén, for instance, has studied Canada lynx. Where these thick-coated wild cats live has a lot to do with where they can find prey. But they also compete for that prey with their close cousins the bobcats. And which cat has the upper hand depends on a whole other factor: snow.

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AS: So when you'd have these really, really, really deep snow years, it kind of gave lynx this competitive advantage. And they'd be able to colonize those areas where there was a lot of snowshoe hares. And when it was really shallow years, they would kind of disappear from those areas and those would be dominated by bobcats.

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MG: So this stuff is complicated. The world is changing in a lot of ways at once. Temperatures are rising, rain and snow are shifting, humans are constantly altering the landscape. And this messiness means that even if a species is shifting in the direction we expect with climate change, we can’t jump to the conclusion that it’s shifting because of climate change.

TLM: We aren't able to, like, manipulate all the different pieces and understand what the responses are in a closed system. We want to be able to say, really rule out that it wasn't all these other things that caused this response. And that's really hard.

MG: If we spot lynx somewhere we don’t expect, we can’t stop them and ask, “did climate change bring you here?” Scientists combine different kinds of evidence, like lab experiments and long-term data on a species’ range, in order to say confidently: Yes, this species is moving, and they were pushed by climate change.

These changes matter for species’ wellbeing and for the health of larger ecosystems. They  also matter for humans, because the species around us shape our lives—from our economies to our cultures to our health.

For example, scientists are worried about disease-carrying ticks and mosquitos moving into new areas.

Or consider the American lobster, one of the most valuable seafood species in the country. Warming waters off the U.S. east coast—plus, potentially, differences in management strategies—have led to dramatic range changes since the 1990s. The lobster fishery in southern New England has collapsed, while farther north in the Gulf of Maine, there’s been a boom.

TLM: And so you could imagine, for example, if lobsters start showing up in your hometown and you are fishing for a living, that could be great news. If you have the gear and the boat and the flexibility to change from the fishery you used to focus on to the one that is now moving in.

That is one end of that lobster fishery. The other, the southern end, there's people there that have spent generations as lobster fishermen, and they have the boats and the time and the expertise, the generational knowledge, to catch lobsters, and the lobsters are going away.

MG: And as plants and animals respond to climate change, people can also lose contact with species or practices or foods that are crucial parts of their culture, history, and connection to where they live.

TLM: For example, we know that the center of sugar maple and maple syrup production is going to be shifting. And there are communities that central to their culture and history is maple sugaring.

MG: As long as we continue warming the planet, we can’t stop our fellow species from responding. But we can try to make things easier for ourselves and the life all around us. Dr. Morelli studies climate change “refugia”—pockets of habitat where the effects of climate change aren’t quite so acute.

TLM: So if we can find those places that seem like they're buffered from climate change, at least for the near future, and protect them from other stressors, they can provide safe havens for populations, or stepping stones as they move to track their climate.

MG: We also can try to make sure the landscapes around us provide species with the food and shelter to stay—or the safe passage to move if they have to.

TLM: So if we think about species needing to shift their ranges, well, we have a very patchy landscape that is broken up with roads and parking lots and other barriers. So we can think about increasing connectivity among areas of habitat.

And then, finally, it's really important that we record what's happening. So monitoring is just really important, and the public can really help with that.

MG: You can actually do this from your phone! There are online databases where you can log the different species you see; we’ll put a few examples in our show notes. 

TLM: The more information we have about where individuals are, when, what they're doing—we can really better understand how species are responding to climate change and how we can help them adapt to these stressors.

MG: Ask MIT Climate is the climate change podcast of the Massachusetts Institute of Technology. Aaron Krol is our executive producer. David Lishansky is our sound editor and producer. Michelle Harris fact-checks our episodes. The music is by Blue Dot Sessions. And I’m your host and associate producer, Madison Goldberg. I also wrote today’s episode.

Many thanks to Dr. Toni Lyn Morelli and Dr. Alexej Sirén for speaking with us, and for showing us the field sites in New Hampshire. You can find more of the show at climate.mit.edu. We’re also on TikTok, Instagram, and Youtube @askmitclimate. And if you’re feeling out of your comfort zone on a climate topic, we’re here for you. Send your questions to askmitclimate@mit.edu.