NATURALIST SELECTIONS IS AN INTERVIEW SERIES PRODUCED BY THE AMERICAN SOCIETY OF NATURALISTS GRADUATE COUNCIL. WE SHOWCASE GRADUATE STUDENT AND POSTDOC AUTHORED WORK IN THE AMERICAN NATURALIST, A PREMIER PEER-REVIEWED JOURNAL FOR ECOLOGY, EVOLUTION, AND ANIMAL BEHAVIOR RESEARCH. CATCH UP ON EXCITING NEW PAPERS YOU MAY HAVE MISSED FROM THE JOURNAL, AND MEET SOME TRULY BRILLIANT EARLY CAREER NATURALISTS!

In this episode, Marshall McMunn talks with us about his new paper McMunn and Pepi 2022: ‘Predicted Asymmetrical Effects of Warming on Nocturnal and Diurnal Soil-Dwelling Ectotherms.’ We talk about the science of thermal activity windows and ant refuge-seeking behavior as well as the stories behind the science, including all the twists and turns on the long road to publication. How do you automate capturing thousands of ants in the Sierra Nevada mountains? How do you craft a paper when the results and explanation for your findings are all completely unexpected? Listen to our conversation and then read Marshall’s full paper here: https://www.journals.uchicago.edu/doi/10.1086/717431.

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Warmed up for more thermal ecology? Email Marshall at msmcmunn@davis.edu!

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Credits

Featured Guest: Dr. Marshall McMunn, University of California Davis

Host, Editor, Producer: Sarah McPeek, University of Virginia, US

Original Music: Daniel Nondorf, University of Virginia, US

Transcript:

You’re listening to Naturalist Selections, an interview series featuring graduate student and postdoc-authored work in The American Naturalist, produced by the American Society of Naturalists Graduate Council. I’m Sarah McPeek and today I’m talking with postdoc first-author Marshall McMunn about his new paper, ‘Predicted Asymmetrical Effects of Warming on Nocturnal and Diurnal Soil-Dwelling Ectotherms.’ Marshall completed this research during his PhD with Dr. Louie Yang at the University of California Davis, where he studied the thermal ecology of ground nesting ant communities in the Sierra Nevada mountains. Different ant species are adapted to different temperature ranges, which affects the window of time they spend foraging outside the nest. In the paper, he and his coauthor Adam Pepi ask how these species’ thermal activity windows will change with warming climates. Their model employs a meteorological phenomenon called the Parton-Logan function, which describes how the changing angle of the sun drives rapid warming around solar noon and slower cooling around solar midnight. Surprisingly, they find that ant species that are more active in cooler temperatures could experience expanded activity windows under warming, but species that are more active in the heat of the day could experience shortened activity windows. I talked with Marshall to shine some light on these intriguing patterns and learn about all the twists and turns along the way to publication.

Sarah

You talk a bit about heat being an ecological resource, and this was a new way of thinking about that part of the environment for me. So I was wondering if you could just explain a little more why you think that.

Marshall

Yeah, that’s an interesting question. I think time is sort of frequently considered as a limiting resource, especially in terms of optimal foraging ecology. I guess that’s sort of some of the basic theory where people started to consider how animals use their time really carefully. And a lot of other folks have worked on thermally restricted activity. I guess the interesting contribution I was trying to make was that temperatures don’t just occur randomly. They’re really quite predictable through the day, and that daily pattern of temperatures has some fairly universal characteristics that might impact these foraging decisions that a lot of animals use. I guess it’s sort of just building on the idea that time itself is a limiting resource for animals in gathering resources or reproducing or anything like that. And a lot of these animals live in these sort of extreme environments where they’re thermally restricted. And so it was sort of through those lenses, I think, that I was thinking that these temperature ranges could be a limiting resource for some organisms.

Sarah

Right. So heat is a part of the environment that can limit your time to interact. Do what you got to do. That makes a lot of sense. Do you think that that’s generalizable to all species, or do you think that that’s pretty specific to ectotherms like the ants that you work on?

Marshall

That’s a good question. I think certainly endotherms pay thermal costs of being less efficient, or even fitness costs in terms of the risk of death if it’s really high temperatures. And so they have optimal ranges as well. But I would expect the effects to be pretty well buffered by their ability to regulate their internal temperature, and so they could have different and more complicated costs. I guess for me, the reason I chose ants was that they displayed this really discrete behavior of either being in their nest or outside of their nest. And if they’re outside their nest, you can say that they made a deliberate choice. Whereas if you run into any other random insects, it might be in a thermal refuge. When you collect it, it might just be flying by. It’s hard to measure the temperatures that they’re experiencing. So I guess that the discrete nature of the foraging decision for ants made it clean conceptually for me that this is their activity window. They are otherwise in their nest. We can characterize what temperatures they’re actually experiencing.

Sarah

Yeah, I think that’s really smart. So ants don’t use thermal refuges when they’re outside of the nest?

Marshall

That’s a really good question.

Sarah

You know, they’re so small.

Marshall

That gets to like the first three years I worked with this data set, I was focused on something completely different, and so I was really interested in spatial heterogeneity and how that interacted with this thermal temperature curve through the day, because this habitat has these sort of scattered pine trees and these beds of pine needles, and then there’s open stretches where it’s just sage brush and bare soil.

Sarah

Yeah.

Marshall

You could imagine the temperature out in the bare soil spikes really high during the day, whereas the pine needles are much more buffered both by the overhanging shade and then also the substrate itself isn’t absorbing as much thermal radiation because it’s not just one flat surface, it’s this sort of matrix of pine needles.

Sarah

Yeah.

Marshall

And so I was exploring the different patterns of how the species overlapped in space and time and really trying to dig down and using network theory. And that’s like a paper I never wrote, basically. But there’s some interesting analysis to be done, but I’m sure they use spatial refuges, and the effect we document is sort of like what’s left over after they do that. This is where we collected them being active. And if you look at the temperature distributions, I think in the final figure, they’re super broad. And I think that’s as a result