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Welcome back to Scishow TalkShow! In this episode Hank learns more about Biocrust explained by Rebecca Durham. Jessi Knudsen CastaƱeda also brings a ball python named Puzzle.

Hosted by: Hank Green
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 (00:00) to (02:00)

*scishow intro*

H: Hello and welcome to the Scishow talk show - that day on Scishow where we talk to interesting people about interesting stuff. Today our interesting person is Rebecca Durham, a botanist who studies plants, and also fungi, and also algae, and

R: Lichens?

H: Lichens. Well what is a lichen?

R: A lichen is a symbiosis between a fungi and an algae and/or cyanobacteria.

H: Ok. So - but - ok. I feel like I got close enough!

R: That was good.

H: So you are - right now your active area of study is biocrusts.

R: That's right.

H: Living soil matrix things...that I do not understand. And they look like they came from another planet, and they're like these tiny little forests that tiny fairies live in, and I think they're beautiful... Are these from around here?

R: They are. Yes. They're from just -

H: Oh wow I didn't even know we had such things!

R: Yeah! Biological soil crusts are really important all around the world in arid and semiarid environments. These are about, y'know, from 20 miles south of Missoula and y'know a lot of the grassland and sage steppe areas...the biological soil crust plays a really big component in the ecosystem. 

R: So ours are a little - most people are only aware of biocrusts in the southwest like in Canyonlands and in that area, because of all the signage and things like that. 

R: Here they are just as important. They're probably a little bit less fragile here than they are down there, because down there you can have just, just a thin layer of biocrust species and then like dirt and sand and it's like kind of humped up. And if you step on it, it shatters.

R: Now here are crusts - you know obviously - are - they've evolved with larger ungulates and things like that, that you know, the elk can walk on some of these crusts and they won't just, you know, fall apart.

 (02:00) to (04:00)

R: So they're a little hardier here, but they can be easily disturbed, um, especially with, um, you know, ATVs or...

H: Right.

R: Recreational, um, vehicles, things like that.

H: Yeah, and these are fragile things 'cause I always (?~2:15) in a National Park and they'll be like "Cryptobiotic crust: Careful! Don't walk on that!"

R: Right. That's true.

H: It's not just dirt.

R: Right.

H: It's more than that.

R: That's true.

H: What's the difference- When I say cryptobiotic crust, that's what they always say on the signs...

R: Right.

H: On the National Park.

R: Yeah.

H: What is that?

R: Well, they- the naming has evolved over the years. They've been called--

H: 'Cause probaby cryptobiotic crust was a little too esoteric.

R: Yeah, it sounds--yeah.  It sounds--

H: It sounds awesome.

R: Yeah, cryptogamic, cryptobiotic, microbiotic, biological soil crust--

H: Okay, that's a little less awesome. 

R: We were kinda using that and shortering it to biocrust, that's the--that's the thing now, it's biocrust.  

H: Where does somebody find, like, if I wanted to go find one of these on my own, where would I go? 

R: Um, anywhere where there's grassland or you know, an area with like, (?~2:59), you know, kind of shrubland, grassland that hasn't had tons and tons of disturbance, you'll find crust.  They--there's higher diversity and more crust coverage on, you know, more north-facing aspects around here.  The aspect can be (?~3:16

H: Does it stay wetter (?~3:20)

R: Yeah, it gets a little more shade, it has a little more moisture, so it kind of--it makes the crust component a little richer than--but even on the, even the really hot south-facing, really rocky stuff in the bunch grasses, like edge of the bunch grass, if you look in there, yup, there's some syntrichia, so, it's everywhere.  I haven't seen one spot on the ranch that we've surveyed, even the places that have been just hammered with disturbance from the past, everywhere has crust.  Everywhere I look, so.

H: How did you--how did you start doing this?  How did you get into the--did you mean to become a biocrust specialist?

R: You know, I've been always interested in lichens.  

 (04:00) to (06:00)

I took Lichenology from Bruce McHugh when I was in Grad School at OSU and so a few years ago, I looked at the lichens, the macrolichens at the ranch and I was at a conference and there was a researcher talking about just kind of his successes and failures in restoration, and he was talking about work that he was doing in Southern California and he said, yeah, we would just put a bunch of stuff in the burlap bag, you know, that was gonna be disturbed, and then we'd go and just shake it over afterwards and he was like, and we grew crust, and I was like, is it just that easy, you know?  If it is, that's fabulous, right, and I wanna do that, so anyway, I met this, I met a PhD student, Mandy Slate, at a moss sort of, gathering and--

H: Wait, a moss gathering?

R: Yeah.  It's actually called (?~4:50), they have 'em every year, it's a really fun--around the West, so I went to this moss gathering and people, you know, they just look at mosses and everyone's just--you know, a bunch of (?~5:07) and moss enthusiasts and it's fabulous.  So anyway, I met her and we, you know, I was like, she was interested and so we started--we have this, a restoration project going for moss and biocrust and right now we've really successfully grown a lot of (?~5:22) which is great, but that kind of like, sparked that collaboration and so, here I am.  

H: So I'm--you've got a bunch of different samples here.  I assume these are all different species of lichen.  Are they all lichen or are they a mix of different things?

R: There's some moss mixed in here.  Now, the algae isn't a huge component, we do see it, and then the, there's also in here, I mean, what we're looking at in biocrusts are lichens, mosses, algae, cyanobacteria, free-living fungi, so what we're really, when we're studying biocrust, we're kind of looking at the macroscopic things mostly.

 (06:00) to (08:00)

So we're looking at the lichen species and we're looking at the moth species, so there's other, there's another--there's more, like, you know, microscopic matrix of other species in there, but really what we're looking at here are the lichens and the mosses, so they kind of grow all intersperced.  In some areas, you have higher lichen coverage than others.  In some, it's more moss dominated.  It partly depends on the site, so, but the diversity is really high in the lichens, so we have maybe about a dozen moss species that we've identified so far in this part of the crust, but there's probably about 65 different lichen species that we've found so far, so the diversity's really high and they're really intricate and fascinating.  So here we have--so this is Peltigera, this is a cyanolichen and so it has cyanobacteria in it, so it's fixing nitrogen as well and that's a really common one in the system.

H: So this is happening on soil rather than like, mostly when I think of lichen, I think of it happening on rocks.  

R: Well, lichen will colonize pretty much any surface, you know, anything that is stable surface and there's actually even one lichen that lives underwater, but most lichens can live anywhere, so you know, when you're looking at the, like, the stuff hanging down from the trees, people are like, oh, look at that moss, that's usually a lichen.  In our area, it's all lichen, so lichens are in the trees, they're on bark, they're on rock, but they're everywhere.

H: Right, right.

R: They're on bones, so--but this is--yeah, go ahead.

H: This lichen wouldn't grow in like, in lots of different places.  It wouldn't just grow as a biocrust or does it--are there some that prefer--?

R: Right, so there are some species that prefer, you know, there are definitely species that prefer certain habitats, so like, all the peltigeras, which this is a peltigera, they all grow on the ground, so you wouldn't find them, like, growing up on the trees or something like that, and so, and there are certain species of peltigera like this one that likes to grow out in the open in the biocrust, but there's also some that are a little bit more moisture loving.  

 (08:00) to (10:00)

They'll be in the forest on the forest floor doing a little bit different thing, like, growing in intersperced with the leaf layer and things like that.

H: So this structure isn't just made of biological life, though.  There's also inorganic matter in there, and like, it feels like it's not just happening on top, it's also happening inside.

R: That's right.  

H: Is that sort of like, the thing that makes biocrust, biocrust?

R: Well, I mean, it's the top few centimeters of the soil, so it's like, you have a lot going in, so you--so a lot of these lichens, they'll make not roots, but they have like, you know, (?~8:54) kind of things that are going in and like, physically stabilizing and then in that, yeah, you have an organic, you know, non-living layer of nutrients and things like that that are all like going on, and even smaller things, and then you have the parts of the biocrust that are sticking up, you know, on top, so it is, you know, like a, you know, the biocrust layer is, you know, what's on top a little bit and then what's below a little bit, so it's the living layer and there are nonorganic components to that.

H: So and that's sort of like a stabilizer, I'd imagine?

R: Exactly, yeah, so biocrusts play a huge role in reducing erosion and you know, soil stabilization and nutrient cycling, you know, there's a lot happening just in these top few layers.  You know, every time a moss hydrates and dehydrates it--there's like a little tiny nutrient pulse of like, shedding from the leaves of the mosses, so there's, you know, nutrient cycling happening on like a really, really small scale.

 (10:00) to (12:00)

H: Are these all dead now or do they still live?

R: They--so the thing about biocrust, which is so fascinating is lichens and mosses are able to tolerate extreme dessication tolerance, you know, that they like drought, they can just hang out for a really long time and they're totally fine, and so what that--actually, that has a really nice word, it's called poikilohydry.

H: Okay, we'll spell it out on the bottom.

R: And that's the ability to, you know, to really just have these drought situations and not have cellular damage, which is what happens to most vascular plants, so these will become biologically active if we sprayed some water, and you know, I should have brought a water bottle and we could, you know, watch them, 'cause the mosses will just go whooo, and that's why they can find, you know, 400 year old mosses like, you know, pulling out of an ice sheet and it's still like, viable, right, because these things, they can just hang out for a really long time and then, you know, come back.

H: So this is more moss (?~11:04) have in here.

R: Yup, that's Gemmabryum caespiticium.  That's one of the real common biocrust mosses there.  

H: I feel like I have probably stepped on this before and not even thought about it.  Is that possible?

R: Yes.  Yeah, yeah, most people, I mean, even--this is--there's all sorts of new slogans, right?  Well, they're not new, but you can say "Don't bust the crust", "Tiptoe the crypto", or "In crust we trust", so if we wanna, you know, and I--we need to spread the word, because so many people, even ecologists, even researchers, will go out and look at the landscape and they won't even think about this soil crust layer either, so--but it's obviously a huge part of the system.  

H: Cool.  So you wanna meet an animal?

R: I would love to meet an animal.

H: Okay, let's do that.

R: Okay.

H: I'm glad I still have my hand lens.  

 (12:00) to (14:00)

R: Wow!

J: This is Puzzle.  Do you know what Puzzle is?

H: A snake.

J: You probably shouldn't touch her right in the face.

H: Oh yeah.

J: Nice work, Hank.  

R: It's not like a cat, where you're like, smell me?

J: No, don't let her smell you, not in the face.  Alright, snake, well, you know, it could have been a lizard.

H: That's true, it could have been one of those glass things.

J: Yeah, legless lizards, yeah, yeah.  But it's not.  It is a snake.

H: It's a constrictor?

J: It is a type of constrictor.  

H: Is it a Boa?

J: Not a Boa.

H: Is it a Python?

J: It is.

H: Okay.

J: Nice work, nice work.

H: How could I tell the difference?  How would I have known if I was the kind of person who would know?

J: You would look at their facial structures but also you'd also study, you know, how they give birth.

H: Oh, right, right, so like, if I was really paying attention.

J: So your Python would lay eggs and a Boa would retain the eggs and then they would hatch inside giving birth to kinda, fake live birth.  

H: Interesting.

J: And she is fully mature.  She's fully grown.  These guys are small.  They're like, 3-5 feet and--

H: I wouldn't necessarily call that small.

J: Well, considering like a reticulated python that gets up 30 feet.

H: Yes.

J: 3-5 feet is pretty small, yeah.

H: Pretty small.

J: They get their name for, can you guess how they got the name ball python?

H: Ball python.  They curl up in little balls?

J: They juggle balls.  No.  No, they roll up into a ball, and a lot of snakes are, a handful of snakes, I guess, will roll up into a ball and put their heads on the inside as a defensive mechanism, but these guys are like, once they do that, you cannot un--

H: You cannot, they're like your headphones if you accidentally put them in the dryer.

J: Exactly.

H: Yeah, it's like that. 

J: It's like that.  Forever.  

H: Just might as well throw them away.

J: Forever.  So, they--that's--they get their common name because they roll up into a ball and they just sit there and that's it.  

H: But Puzzle is happy right now, so--

J: She's not feeling upset.  The first sign that I would know that she was upset is she would hiss.  She would exhale a bit, she'd be like, ohh (?~14:00).

 (14:00) to (16:00)

But if she was scared, yeah, she'd roll up into a ball, but look, and we call her Puzzle because she has a really cool pattern on her, and if you look closely, look at some of these--

H: Eyespots?

J: Yeah.  

H: Or like an alien.

J: It does.  It looks like an alien head with eyes.

R: Yeah.

J: So when they roll up into a ball, it actually looks like faces and so whatever predator is going to be like, whoa, whoa, whoa, I didn't--I don't wanna take up on ten of you.  I'm out.  

R: How long do they live?

J: They can live up to 30 years.

R: Wow.

J: Average is about 20.  I shouldn't say up to 30 years, I mean, 30 is really doing really good.  They can--the oldest was 48, I believe, but average is about 20, 10 in the wild because they do have quite a few predators.  They are also hunted by humans.  They were captured a lot for the pet trade and there's still a bunch of them like, 30-50,000 are still exported from Africa into the pet trade.  They're also taken for food and for leather, so right now they're not threatened, but they are kind of close, because they can adapt so well to habitat destruction or change, they're actually doing pretty well.  Have I talked to you about how snakes constrict their prey?

H: No.

J: So new research.

H: Okay.

J: We used to think that snakes would strike and then suffocate their prey, right?  And every time--I was taught ten years ago that they would--prey would exhale and they would squeeze tight and then exhale and squeeze tighter and tighter until they couldn't--yeah, so that's not how they actually kill.

H: That's wrong.

J: Well, they might do that, but the thing that's actually killing that animal is they are squeezing so tight that they're stopping the blood from pumping from the heart into the rest of their bodies so they're actually having a kind of a heart attack, 'cause they can't get the--

H: Right.  They just pass out, it's like a headlock.

J: Yeah, and it's quicker than suffocation, so these guys are like, the best predators, the most humane, I guess, predators?

 (16:00) to (18:00)

H:  Well, except for the part where, you know, you're eating them alive sometimes.

J: Well, they--well, yeah, yeah.  It's just sometimes though.  These guys are cool because like, some other python species, they don't just lay their eggs and leave.  Most snakes do that.  So these guys will actually curl up on their clutch of eggs and sit there until they hatch, which is about two months.

H: And not eat, not leave?

J: Nope.

H: Just stay there the whole time?

J: Just stay there.  And they think the main reason they do that is to prevent moisture loss and so that they can be a nice heavyweight and produce a heavy offspring, but they can also, which I think is super cool, they are ectothermic, so they can actually heat up their clutch of eggs if it starts to be too cold up to seven degrees Fahrenheit, so they will shiver and then raise the temperature to make sure they don't get too cold.  I think that's awesome. 

H: Yeah, this whole differentiation between warm-blooded and cold-blooded, it's all--there's always exceptions.

J: Yes.  Yes.  Always.

H: Always a fuzzy line.

J: Do you want to try and hold her?

R: Sure.  

H: It's always a little surprising how cold a snake is in temperature, for me.

R: Wow.  Cool.  She's beautiful.  

J: I like how they are so different on the bottom as opposed to the top.  They have these little tiny scales on the bottom and then these big scales on the--I'm sorry, little scales on the top and big scales on the bottom (?~17:36)

R: It's interesting to feel the muscle move, like, in your hand, like.  Now, how--what is the muscular system like for a snake?

J: So, I mean, the whole--they have just the same (?~17:47) two really long (?~17:49) that go down the sides of their spine there, but the way that they move is they move against themselves and so they're push--she's propelling from back here, propelling herself forward and then she'll see, see, she's kind of kinked around my finger here.

 (18:00) to (19:51)

So she's going to then use this muscle to pull the rest of her body forward.

R: Oh wow, cool.

H: I've heard that the muscles of snakes are more like the muscles of fish.  Not like, physiologically--well, physiologically, not like biochemically or anything, but because they are, you know, it's all about this motion--

J: Yes.

H: And so it's muscles pulling on muscles.

J: Yes.

H: Rather than most of our muscles pull on bones.

J: Yes, yes.  Yup.  It's muscle against muscle work for them, and that's how they're--yeah.  And then, they also, it's not just muscles helping them move.  It's also their scales.  So if you run your finger this way, it's very smooth, so she'd be going forward,  but if you went this way, you could actually catch a scale.  It's uncomfortable for her so I don't want to do it, but you can actually catch a scale because they're all facing this direction so if she's trying to go up a  tree or she's trying to go up a rocky area, those scales will actually prevent her from slipping backwards and so she can continue to use her muscles and your scales.  Good girl.

H: Easy enough.  Well, we're very lucky to have you in town and also Puzzle in town.  That's very cool.  If you wanna see more of what Jessi does, you can check out her--she has a YouTube channel where she talks about all of the animals that she works with.  You've got over 80 animals at Animal Wonders.  You can find that at and thank you so much for joining us.

J: Thank you for having us.  It's always so fun.

H: And thank you or joining us.  Remember, don't bust the crust.  Thank you all for watching.  If you wanna watch more, go to and subscribe.