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.

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

Listen on Spotify and Apple Podcasts!

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 of them being across all these various habitats.

Sarah

So what led you to move away from that initial interest in the thermal refuges to where you are now?

Marshall

I needed another paper to finish my PhD and this was sort of the low hanging fruit.

Sarah

Got it. Yeah. So did you know, were you familiar with the Parton-Logan function before beginning this, or is that totally new?

Marshall

Not at all. So the way I came about this idea was just digging through all these tons of analyses. That R script never went anywhere, but it was like thousands of lines long. And at one point I was like, what happens if you bump up the environmental temperature, like which ants thermal niche overlaps more or less with that sort of like simulated future temperature? And I got that negative result in the last figure of this relationship where the ants that are found at higher temperatures actually lose activity time when it warms up, which I was confused by and I assumed I did something wrong. And it took me a while. I sort of thought through it for a few hours and was like, oh, it might have to do with this second derivative of the temperature, like not the change in temperature per se, but that it’s actually changing at different rates throughout the day, that it’s stable near the peak and the minimum temperatures. And that’s when I sort of started looking at who has done this sort of thing before the climatology literature and found the Parton-Logan function and was like, oh, okay, somebody’s named this function that we see and its characteristics have been explained from basic meteorological principles. Cool. That’s good. That’s citable.

Sarah

Yeah.

Marshall

It was sort of a circuitous path that led me to like, oh, this is a general characteristic of daily temperatures. It very much wasn’t like I had the idea that I went out and tested it. It was like I stumbled on the result accidentally and then sort of had to explain it because I couldn’t find a mistake in the code. In trying to explain what I assumed was a mistake, I was like, oh, okay. Actually, it’s this shape of that curve that’s driving that pattern.

Sarah

That’s so funny. I feel like so many projects come out of the published work is this neat leading the reader through to a nice, neat conclusion, but the actual process of doing it is just kind of what’s going on. This makes no sense. I totally screwed something up.

Marshall

And at one point I wrote the paper. Like, that sort of like telling the narrative.

Sarah

I was going to ask. Yeah.

Marshall

But I got feedback that it was sort of hard to follow. Like, why are you showing us this result and then going back and explaining it? I thought it was like a neat sort of like, here’s how science is done. But I think people are sort of have an expectation and reading a paper of here’s an idea here, we’re going to test it and we’re going to then take it out into the field. I think it’s just sort of easier to digest, at least. I don’t know. I don’t think I was talented enough of a writer to make it a compelling story.

Sarah

Yeah. I always wonder if that’s, I don’t know, I don’t want to say correct, but an honest way to tell our science. I’ve often struggled with that in my own work because I’ve also had many projects where it’s been: I definitely screwed something up. This makes no sense. I’ll never be able to answer this and then coming back to a conclusion after doing a lot more work, but then you have to write the paper like you had that conclusion in mind from the start. And I don’t know, that just feels kind of gross to me.

Marshall

Yeah. I feel that tension for sure. It’s like I want as many people to understand this paper, and so I’m willing to sort of like, provide these in an order in the expected way. But then occasionally you get feedback that’s like, oh, it has to be hypothesis driven, and you need to sort of lay out the hypothesis at the end of the introduction. And yeah, I start to sort of feel that that narrative misleads the reader rather than just sort of helps them along. I feel like there’s a real trade off there in terms of how much we embrace that sort of expected narrative structure for paper.

Sarah

Yeah. I just think it’s funny because we all go through this and we can relate to this, and yet we won’t talk about it when we share our work.

Marshall

I know. Yeah, it’s funny. And I tried to sort of buck the tradition with this one, but the resulting paper is like, people sort of read it and said, like, I don’t think it flows that well. I understand that’s the order that it happened in, but it’s hard to understand that way. It’s something we all struggle with, I think.

Sarah

Definitely. So it sounds like you were very surprised by your predictions. Clearly that took a lot of work to figure out what was actually going on there. So how do you think you or another researcher would test these predictions under warming? Like the fact that a species that has a cold, active window would actually expand that window during warming? How would we look at that?

Marshall

Yeah, that’s a really good question. It’s easy in the simulations because they’re not real animals, so they don’t misbehave in a lot of complicated ways. Real thermal physiology is so incredibly difficult and complicated. I feel like this is sort of an interesting example of this behavioral pattern and an expectation of one of the many ways that the animals might experience climate change. But then they have so many compensatory mechanisms that are sort of available to them that you might not even expect to see a difference in fitnesses or population numbers because they could easily expand their seasonal range if that’s available to them. Or you could actually see the effect of this process through species ranges, like shifting at different rates, or they could switch prey items and it’s a slightly riskier prey. I guess there’s so many different compensatory mechanisms. I reached out at one point and almost started like a Museum collection based project to try to see if species ranges were shifting or species phenologies were shifting in accordance with whether they were diurnal or nocturnal. And so to try to test this, but it was such a course metric diurnal nocturnal. And no one writes collection time like the actual time of day.

Sarah

True.

Marshall

On a Museum specimen. And even after doing this work for a while, I still don’t write the collection time on most like accessions that I do because it takes a lot of time to add that little piece of information. But anyway, I guess I was sort of thinking about doing a Museum sample sort of study, but the short version is no one records collection time and the diurnal nocturnal dichotomy was only working. Lepidopterin a lot of organisms are flexible based on where they are, what time of year it is, and I sort of had enough skepticism going into the project, but I didn’t pursue it any further.

Sarah

Yeah. I think it’s a really smart idea. I think another challenge with that could be that I don’t know how many species there would be good records of their thermal physiology dating back through time. I know you had to do a lot of that work for your Ant species to actually measure what is their thermal range in the lab. But I don’t know if that data exists for a lot of other creatures.

Marshall

Yeah. And another abandoned project was the measurement techniques for ectotherms to get their thermal physiology like what’s their CTmax, what’s their CT min? They’re really challenging to standardize across studies. For this study, I think the CT minimum Max only made it to the supplement. But for this study I collected in the field and sort of brought the lab to them. So they were tested immediately. But that’s not standardized across different researchers. Some people will drive a few hours, some people take it and put it in the lab and it acclimates there and then they test it. And so when you get into the sort of small details just because the ability of organisms to acclimate is so strong that it’s a challenging metric to standardize. It’s hard to use the literature for some of those things.

Sarah

Definitely. Yeah. Getting into one of the small details, I do want to mention that I loved your method for collecting the ants. I thought that was so ingenious because I guess I was picturing you out there with a magnifying glass just looking on the ground. It’s so much smarter to pit trap them.

Marshall

That’s what I did the first year.

Sarah

Yeah?

Marshall

I think I did like baits. And so I put out tuna and honey, which is like pecan Sandy’s, which are traditional tuna. Yeah. So really like tuna. Tuna and hot dogs are available worldwide and ants love them. Like, universally, ants love tuna, hot dogs, and Pecan Sandy’s, which is like one specific cookie that everyone has sort of gravitated towards. So you have your bases covered with your different Ant diet types. If you put out pecan Sandy’s and hot dogs Fortuna.

Sarah

Good to know. Good to know.

Marshall

Yeah. So I was walking this transact constantly and pounding and identifying the different ants. But you could imagine it’s hard to work 24 hours a day. And so the amount of data that I was getting for the effort was just tiny.

Sarah

Yeah.

Marshall

And so I sort of needed to automate the collection process somehow, and it took a long time to figure out. But at one point I was talking to a friend and they suggested that I sort of adopt, like, an Ant Gatling gun, which was like, there’s like an automated Chamber that swivels around to the collection funnel. And then I sort of looked into it and someone had actually done this before, sort of like small computers were available. And so their version of it was huge. It was like 3ft by 3ft by 3ft. And so they dug like, this grave sized hole for every device that they use to monitor arthropods.

Sarah

Wow.

Marshall

It’s an insane amount of work. And it was also just too much soil disturbance for ants. Like, they like soil disturbance. And so if I dug this huge hole, I don’t know what I would necessarily be measuring Ant activity, but it’s probably just given that they’re attracted to soil disturbance.

Sarah

They would gravitate to that. Yeah.

Marshall

That wasn’t an option for ants, so I needed to make it smaller. And fortunately, the open source hardware community is this really well documented and supported community where everybody puts their code online, everybody says, what hardware and puts their wiring diagrams. And so it wasn’t starting from scratch. They were sort of like, this is how you control the rotation with a stepper motor. Like, this is how you make a data logger. This is how you record data to an SD card. All of those components were there individually. I just had to put it together into a working all at once machine and then make it so it didn’t break anymore. Yeah. So it was 150 or so collection days, but it was using 15 traps, usually not simultaneously, because there was a digging in period at the beginning because, like I said, ants are attracted to soil disturbance. And so basically I left the trap sitting there, not collecting for the first day, and then it automatically kicked on 24 hours later. And I sort of, like, uncapped it to let the ants fall in. Yeah. So it was a fun project, but, yeah, open source hardware is really cool. It’s amazing what people the problems people have already solved. Basically, if you can figure out how to Google it, then you can find instructions on how to build it.

Sarah

Wow. Yeah. That’s a great resource. Like, you learned a lot about the weather and mechanics and all kinds of stuff with this project.

Marshall

Yeah, it was cool. There’s a spin off paper that’s like just how to build these traps. Basically, nobody reads any of the papers that I write, but that one is, like, the most cited. I don’t know why. I think it’s maybe just like an example of open hardware. Most people aren’t building their own arthropod collectors, but just in terms of citations, it’s funny that that one actually gets the most. Yeah, I guess it’s been helpful. So that’s good.

Sarah

Where is that published?

Marshall

Hardware X, which is like an open source hardware Journal, the inaugural issue of that Journal, and so they made it free to publish there, and it was open source, so that’s why I went with that one.

Sarah

That’s awesome.

Marshall

Instead of like an entomology Journal.

Sarah

Well, you’ve got a really wide breadth of publications then. Hardware, Entomology. AmNat.

Marshall

Yeah. It’s been fun.

Sarah

Well, it sounds like you’ve had a really fascinating journey And I’m really glad we got to see a piece of it in AmNat and I’m also really glad I got to hear a little more about the exciting and confusing and complicated project behind it.

Marshall

Yeah, definitely. It came out of a complete accident, so I’m excited that it, hopefully is a paper that people enjoy and others can build off of.

Sarah

I think it definitely is.

Marshall

Thanks.