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The Secret Life Of the Sonoran Desert


I'm Ira Flatow. Now for a look at the lush life of the desert. We're here in Phoenix, Arizona this week, at Arizona State University, where it's a sunny 76 degrees. Spring training is in its final week. You'd never know from the swimming pools and the golf courses that Phoenix sits in a desert. The Sonoran Desert is about 100,000 square miles and much of it in Arizona.

But before you start thinking sand dunes and tumbleweed, this desert is anything but a dry, dusty wasteland. Just 30 minutes outside the city, you'll find one of the most diverse desert ecosystems in the world. If birds, flowers and frogs float your boat, there are plenty of them here, along with reptiles and tiny microscopic life that's not on your tourist map.

We also have some photos on our website, some scenes from the Sonoran in springtime. You can see those at sciencefriday.com/sonoran. There are some great photos out there for you to look at. And for those of you in the northern parts of the country, where snowdrifts still cover the ground, just soak in the rays coming from your radio or your smartphone as we attempt to transport you, at least for a little while, to the lush desert Southwest.

And if you're here in the audience, we invite you to step up to the microphone and ask a question, and you can also tweet us, @scifri, @-S-C-I-F-R-I, or go to our website at sciencefriday.com for more information.

Let me introduce my guests. Kevin Hultine is a plant physiologist at the Desert Botanical Garden in Phoenix. Thanks for being with us today. Ferran Garcia-Pichel is a microbiologist. He's also the dean of natural sciences, professor at Arizona State University in Tempe. Thank you for being with us today, Dr. Garcia-Pichel.

FERRAN GARCIA-PICHEL: Pleasure to be here.

FLATOW: You're welcome. Jon Davis is an environmental physiologist and course manager for biology at ASU's Downtown Phoenix campus. Thank you for being with us today, Dr. Davis. Let me begin with you, and let's just back up for a bit and describe the Sonoran Desert for us. What is - as a desert? Does it get much rain here?

JON DAVIS: Like most people think of deserts, it certainly doesn't get most rain, and what makes it a little different than what you might imagine is that it's highly seasonable rain. So we have a wet monsoon season in the late summer, we have a sometimes wet winter in which we get rain from maybe January, February, a little bit in March.

Those two pulses of rain are what sets the Sonoran Desert apart from some others. It's dry the rest of the year between those times. When it does rain, we certainly are only getting maybe a couple of inches overall. Four inches is a good year in many cases.

FLATOW: So it's not the tumbleweed desert we see in the movies, right?

DAVIS: Not at all. Those pulses of rain really do allow the desert to come alive, and anyone who's been out in our area in the last month or so has really seen that because we had some decent winter rain.

FLATOW: Yeah, and we have those pictures up on our website, at sciencefriday.com. Dr. Hultine, how much rain does it get in the desert here?

KEVIN HULTINE: Well, it varies across the region of the Sonoran Desert. It could be anywhere from about two inches or less in some areas up to 25 inches up in some of the mountains.

FLATOW: Twenty-five inches?

HULTINE: Yeah, you know, we have these - an area called the Sky Islands, and some of those mountain ranges do get quite a bit of rain. But, you know, for instance here in Phoenix, we get about seven inches of rain per year, and it is bimodal, as mentioned earlier. And we get roughly half of that rain in the - during the summer monsoon in July and August, and the rest comes in these low-intensity rainfall events during the winter.

FLATOW: Can you notice global warming having any effect on the weather, the rainfall, or any of that stuff?

HULTINE: There has been a - you know, we've been in a drought for the last decade or longer. Whether you could attribute that directly to global warming or not is debatable. But for sure the climate model suggests that this region is going to experience some of the most dramatic impacts of global warming in North America in the next century.

FLATOW: What do you mean by that?

HULTINE: Well, temperature here, if you look at the models, temperature by the end of this century is predicted to change by anywhere between four and 10 degrees Fahrenheit. So far over the last 30 years, temperature has increased in the region by one and a half degrees Fahrenheit. So that's a pretty dramatic change if that does, in fact, come to fruition.

FLATOW: Wow. Are we looking at the kind of weather that we're seeing in Australia, that super-hot summer? They actually had to add another color to their temperature chart because they couldn't go that high.

HULTINE: We are potentially looking at that kind of scenario, yes.

FLATOW: Wow. What makes this desert different than other deserts? What makes the wildlife here different than other deserts?

HULTINE: Well, I think there's two things. Again, we do get a fair amount of rain in the summertime. But also this is sort of a convergence of plant life in particular from multiple regions, from the subtropics even from the temperate forest, as well. And so we have this convergence of plant life that supports a lot of fauna, as well, that you don't get in a lot of - in most of the other deserts.

FLATOW: Dr. Garcia-Pichel, you study something we don't normally associate with deserts. Those are the tiny microbes that we never - it's not on the tourist map to go out and see the microbes, but you see them.

GARCIA-PICHEL: Well, we see them, and they're starting to become part of the tourist maps.

FLATOW: Is that right?

GARCIA-PICHEL: Yes, if you go to some of the national parks, for example, there's - in the area, in the Southwest, you see some of these announcements where they tell you that these microbes exist and that they play an important role in the ecosystem, and they tell you to be careful about trampling on them.

FLATOW: Is that right?

GARCIA-PICHEL: That's correct.

FLATOW: So what role do they play, then?

GARCIA-PICHEL: Well so in general, microbes are as important in the desert as in any other ecosystem. Only - the only difference, I would say, in terms of the role is that because the general lack of water and the extreme temperatures that are typical of the hot desert, like the Sonoran Desert, restrict a little bit the total importance of plants, for example, in the ecosystem.

So while the Sonoran Desert is luxurious if you look at it from the level of standing on the ground, if you look at the surface area, most of the surface is actually not covered by plants, like say in a temperate region. Those areas, typically now what happens is that the light from the sun can now hit directly the mineral part of the soil, creating a habitat for microbes that run photosynthesis.

So now you have, in the deserts and not in other ecosystems, very much so, microbial communities working in the soil surface or on the soil surface in the first two or three millimeters of the soil where light can penetrate an eighth of an inch or so.

FLATOW: So they must have to be very strong microbes.

GARCIA-PICHEL: They are indeed very strong microbes. They are extremophiles, as we call them, in many respects. The surface of the soil, the surface of the dirt in the desert when it's dry, in the Sonoran Desert, can get extremely hot in the summer. As you heard before, microbes are also exposed to this pulse nature of water, and they can only do things when water is available.

But they have no roots. They are too small for that. They cannot regulate their temperature. They're too small for that. They're exposed to the ultraviolet in the sun for months, and so they have to have developed specific adaptations to cope with these extreme conditions.

FLATOW: So they develop their own sunscreen?

GARCIA-PICHEL: That's correct. That's one of the things we studied in my group, and so some of these microbes actually can put up to 15 percent of their own bodyweight into one single sunscreen that they put up to withstand the ultraviolet rays in the sun. And in so doing they can, for example, change the color of the soil surface. And in so doing, they change how the soil surface reacts to light and how hot it gets so what we call the albedo of the soil.

And so these adaptations of the microorganisms have implications beyond their own small sort of small millimeter-sized areas.

FLATOW: Fascinating stuff. Dr. Davis, you study Gila monsters.

DAVIS: That's correct.

FLATOW: Are they really monsters?

DAVIS: I don't think they are. To most folks that aren't from around here, you might hear that name, and you've heard that they're venomous, and they're dangerous and things like that. But really, as was just commented, they're also sort of extremophiles. So I've become very fond of these animals just for their sheer ability to survive sort of life on the edge under these highly seasonal, very harsh conditions.

FLATOW: And so what is their niche in this little ecosystem here?

DAVIS: They're really a mid-level predator. So most people are familiar with things like rattlesnakes here in the Sonoran Desert, and they're right along that line. So they're certainly not a top predator in the system, but they're right in the middle and prey on things like anything that lives in a nest, so rabbits and rodents and birds that nest on the ground. That's what they are consuming. And they're trying to avoid things like coyotes and bobcats and mountain lions.

FLATOW: Describe what they look like, and how would you know if you saw one?

DAVIS: They are very distinctive. So people still confuse them a bit, but they're a large lizard. They're roughly 18 inches from head to tail on the large end of the scale so about the - a little longer than our nameplates up here. They are orange and black patterned and so not quite tiger stripes, but they have that same feel, where they have the orange mixed with the black, and that really allows them to disappear when they get under the shadow of branches of plants.

The sun comes through and gives sort of an orange light onto the ground. The shadow makes the dark. And they'll virtually vanish. The orange is also valuable because it's what's called a warning coloration. Because these animals are venomous, oftentimes what you see with things like poison arrow frogs, a very bright color to tell predators don't mess with me, I'm dangerous.

And so they sort of have that combination of color and pattern that helps them with camouflage and also with some defense.

FLATOW: But they're not out there lurking, waiting for you, are they?

DAVIS: No, most people, even lifers in Arizona, natives, often haven't seen them, even if you go hiking frequently. They're secretive. They're actually seldomly on the surface, and so if you're really anxious to see one, go now. March is when you tend to...

FLATOW: Not right this second.

DAVIS: Not now but in a couple of hours. Head out to one of our mountain ranges around town here and go on a hike, especially in the earlier morning hours up until 10 or 11, before it gets too warm. You might see one out basking. But generally they're fairly secretive.

FLATOW: We're going to take a break. When we come back, we're going to take questions from the audience. Don't be afraid to get up to the microphone there and ask a question. We'll come back and talk lots more about the Sonoran Desert. Stay with us. We'll be right back after this break.


FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY from NPR.


FLATOW: This is SCIENCE FRIDAY. I'm Ira Flatow. We're at Arizona State University in Phoenix, talking this hour about the secret life of the desert with my guests: Kevin Hultine, Ferran Garcia-Pichel and Jon Davis. And you can ask a question right here in our audience, and let's - yes, young man, ask your question.

UNIDENTIFIED CHILD #1: Why are some saguaro cactus crested?

FLATOW: Why are some saguaro crusted, did you say? Crested.

HULTINE: I think what he was getting at is why do they have a really rare crested shape. And that's a great question. There's a very small number of saguaros that take on this sort of fan crest at its top. And that is just a very rare mutation that is non-lethal. And so occasionally you'll come across a plant that has that crested shape. Again, they're extremely rare.

I think if you find one happening to grow in your yard, you should take plenty of pictures of it and make sure no one takes it.


HULTINE: And enjoy it.

FLATOW: We have plenty of pictures on our website at sciencefriday.com/Sonoran, you can go see the pictures up there. Thank you. One thing that I learned in the research for this: Is it true that the arm on those cacti, they take like 75 years before they grow that arm?

HULTINE: You know, it depends on the location. If it's a wet area, relatively wet, the plants could grow quite a bit faster. And so you may - they may produce arms in 40 or 50 years.

FLATOW: Oh, just 40 or 50, OK.

HULTINE: But yeah, it takes some time, some energy.

FLATOW: All right, let's go to another question in the audience. Yes?

UNIDENTIFIED CHILD #2: So I heard about Gila monsters, and so like what are some of like the common animals that they would eat?

DAVIS: So Gila monsters aren't very fleet of foot. They're slow. They go out and search very slowly for their prey, and they use their sense of smell to detect these things. So what they tend to find are animals that are in nests. We're talking quails, they lay their eggs on the ground so they can find those eggs and eat those; any rabbits or rodents, some of the desert mice and desert rats that will have their babies in nests, they'll actually go and eat those guys because they're so slow they can't run fast enough to catch something like an adult rabbit. So they eat nestlings, always.

FLATOW: Good question. I have a question, a tweet came in from Yamina(ph), who says: Are there any flora and fauna that live only in the Sonoran Desert and nowhere else? Who wants to jump in on that. Dr. Hultine?

HULTINE: Well, there's - one of the things that defines the Sonoran Desert is the type of vegetation that you find here. And so you have a number of plant species I know of that are only specific to the Sonoran Desert. For example, the giant saguaro only grows in the Sonoran Desert along with many other cacti species.

FLATOW: Why is - that's amazing, only in the Sonoran.

HULTINE: That's right.

FLATOW: And what is it about that - what do they need that they don't get in other places?

HULTINE: It's a combination of enough rainfall at the right time and no frost or very little frost. Saguaro has very low tolerance for frost. It has some...

FLATOW: Like one day maybe?

HULTINE: Yeah, yeah, one day, depending on how low the temperature gets. But it's just a combination of environmental qualities that allow some of these plants to occur here and not anywhere else.

FLATOW: Yes, ma'am?

UNIDENTIFIED WOMAN #1: Hi, yes, I guess actually following up on something you were just saying. Is there any other way that plants in this area, there's such a fluctuation in one day from the daytime temperatures to the nighttime temperatures, that they've adapted to handle those temperature changes?

HULTINE: Yes, there's the - to a certain extent, again, if there's very little frost, then they tend to do quite well. Cacti plants in particular have a very unique strategy for photosynthesis, and that is they take up carbon at night, when it's not quite as hot, and then they - when the sun comes up, they fix that carbon into various materials that it uses for energy.

And this is what a lot of desert plants do, especially succulents like cacti, and that's a way to deal with those really large temperature gradients that you find over the course of a day.

FLATOW: Dr. Garcia-Pichel, let me ask you a question about these extremophiles, these bacteria, the microbes you study. Would they be - are they very old? Would they have been around at the beginning, as being maybe the first forms of ancient life? And are they the kinds of things you might find on Mars or other places?

GARCIA-PICHEL: Yes, these are two very interesting aspects of these communities we study in the desert. In a way, if you think about it, these communities of soil crust that, like, we call them, that grow in the plant interspaces in the desert, for example, but also in polar areas, where there is also no plant cover, there is no reason they wouldn't have been able to grow on the continents before plants evolved.

And it just so happens that plants, for example, as my colleagues here will surely know, evolved only 400 million years ago or so and probably around the Devonian, the era we call the Devonian, whereas the continental surfaces are much older than this. Actually, the continents have been present on Earth for a much longer period than those 400 million years.

And so what we think is that crust or crust communities such as we find now only in desert areas, where no plant cover exists, was actually the whole of the terrestrial ecosystem globally during most of Earth's evolutionary history. So yes, they are important probably in this regard. Now the problem we have with this is we don't have proof of that, or very direct proof, because things on deserts or things on terrestrial surfaces do not fossilize very well.

And so fossils of these communities are very hard to come by, and the only ones we have are not very old or not very telling. So yes, they are very old, and yes, if we think about things like potential life on Mars, if there was life on Mars once, as the planet dried out, potentially these communities that we have now of microbes in deserts would have been very good potential analogues to see if there is any signatures that they may have left in there.

So in this sense these communities we study, and they are important to our ecosystem now, are also important in terms of looking at questions of that - the nature that you mentioned.

FLATOW: But even though they're tough little critters, they can be damaged, right?

GARCIA-PICHEL: Oh yes, they can be damaged. They are very tough against temperature extremes and ultraviolet radiation and so on. And yet the ecosystem as a whole is not very tough against compressional forces. So you can damage those crusts very simply by trampling, by, you know, walking on the desert, by having vehicles run across the desert surface.

And so this is really an environmental problem now, not in the past or in Mars, but this is a real thing that occupies us now, because when you trample and destroy this cover, then what happens is that the soil becomes a lot more erodible and a lot more sensitive to, say, erosional forces from wind and water. And we have these big haboobs. These are typical things we know, the locals here, as dust storms and so on, because the desert surfaces are no longer being kept by its microbial cover.

FLATOW: Wow, interesting. Yes, ma'am.

UNIDENTIFIED WOMAN #2: I'm also interested in these super-microbes and their ability to self-create sunscreen or sun protection. And I'm curious if there might be something we could learn that would applicable to humans and sun protection.

GARCIA-PICHEL: Sure enough. We are always trying to learn things from what the microbes can tell us, right? In this case in particular, the adaptations with the microbial sunscreens, we have studied those secondary metabolites, as we call them, the chemical nature and the potential biological applications that they have. And of course they maybe have an application in terms of biomedical application.

Some of these compounds that we've isolated from microbes in the crust have actually biological potential. Some of them surprised us with activities that are anti-cancer activities. So all of these potential - you ought to always look at what this novelty may bring to us.

FLATOW: Let me - before I go to a question here, speaking of human applications, could there - speaking of the Gila monster again, could there be medical applications to the venom or the saliva of the Gila monster?

DAVIS: There are, in fact. There are several proteins in the saliva, in the venom of the Gila monster, that scientists have been studying for more than decade now. One particular component actually is effective in treating diabetes and has gone to market by one of the pharmaceutical companies. Some of the other research that's ongoing now are related to things like Alzheimer's and dementia treatment. One of the proteins in the Gila monster saliva is actually thought to trigger memory, help that predator remember not to mess with the Gila monster. It's an evolutionarily beneficial component. So by extracting that, can we use that to then improve memory in adults, in humans? And at this stage, of course, we don't know that, but that's the type of thing that people are looking at.

FLATOW: That's fascinating. Yes, ma'am.

UNIDENTIFIED WOMAN #3: My question is for everyone who has an armless saguaro and is waiting impatiently for it to have an arm. So we've had our house about seven years. We don't know how old our saguaro is, but it's about 15 feet tall. And finally last year, it bloomed. We hadn't noticed it ever bloomed before, and we see a thickening a little in the middle. Does that mean anything?

FLATOW: It's going to have a baby? No.


HULTINE: So that's an interesting question. What we typically find is if you look at a saguaro that has small arms just start over the last decade or so, you'll find that at the point where the arms start to come out of the main stem is that the stem itself is much narrower at that point. So I'm not sure your - in your case what to expect. But given that it is 15 feet tall, my guess is you probably will start seeing some arms, but it'll be a slow process. And I hope you...

FLATOW: You know, you can see homeowners in this state have some other things to worry about than they have in other states. Certainly, you know, since this is the only place where the saguaro grows, you're anxiously - we're waiting for the roses to come out, and you're waiting for the arms to come out...


FLATOW: ...on a cacti. It's kind of - it's unique. It's wonderful to hear. Yes, ma'am.

UNIDENTIFIED WOMAN #4: Hi. You mentioned earlier about the weather extremes and the changes in the climate. Any predictions or expectations about what's going to happen to our weather and our flora or with the weather changes that you're seeing?

HULTINE: Well, one thing that is - it's hard to predict and it depends on the plant, but there's one potentially positive impact, I guess, if you're a homeowner in Arizona, is that there's a lot of really charismatic cacti species that are somewhat similar to saguaros that are very limited by frost. And you don't see them actually in Arizona. They only occur in parts of Sonora, Mexico and Baja. We may see some of those species start to migrate northward into Arizona over the next century.

But otherwise, the - when you increase the evaporative demand as much as is being predicted, it's going to have a very deleterious impact on a number of plants and plant species. And we've already seen some evidence of this just based on what happens in Phoenix. We have what's known as the heat-island effect, so nighttime temperatures here are very warm. And plants have a hard time just dealing with that extra heat load that's on them and that extra evaporative demand. So we'll see what happens, but for the most part it's going to be a tough time for many plant species, but we will see a change in the distribution potentially in its range.

FLATOW: I'm Ira Flatow and this is SCIENCE FRIDAY from NPR. A tweet coming in from Andrew Middleton(ph). It says: What concerns do your guests have about large-scale solar operations planned for Arizona? Are we afraid that those desert creatures are going to be affected? No? Dr. Garcia-Pichel?

GARCIA-PICHEL: Well, so far I don't have a lot of concerns about that, in that it's always, I guess, a compromise. So we may derive a lot of benefits from having more solar power plants being set up. Certainly the populations of plants and animals and microbes and what we call the biogeochemistry of the desert will change very much locally. But again, it's not that we are thinking of turning Arizona into the power plant for the West and so...

FLATOW: Right. Let me go to a question here in the audience. Yes, ma'am.

UNIDENTIFIED WOMAN #5: Hi. So, in the - I've been here since '93, and the amount of desert that's disappeared since '93 is incredible. You know, there used be a lot of desert in Scottsdale. Now there's practically none, and now it's going out further and further. And is there anything in place to actually ebb that tide? Is there anything that is being - actively being done to make sure that it stops at some point...

FLATOW: Dr. Davis?

UNIDENTIFIED WOMAN #4: ...before it's gone?


DAVIS: It's a concern, I think, probably for all of us. Any time you have the expansion and the urban sprawl that is pretty characteristic of Arizona as a whole, you end up with some sort of habitat loss and certainly changes to existing habitat. I'm not aware of anything that is slowing that, especially with the rate it was going before the economic downturn. Now that Arizona is starting to bounce back, I would expect the foot to go back on the accelerator and those homes to keep going just to fuel the economy even more.

In the state it's driven by that. I would like to see there be some limitations - growth boundaries, city boundaries and things of that nature - but I'm not aware of anything currently.

FLATOW: Well, I think we have time for one more question before the break, and I'm afraid to ask - the gentleman says - his T-shirt says: I am silently correcting your grammar.


FLATOW: So I will be very careful how I approach this.

UNIDENTIFIED MAN #1: It's mostly for the Cronkite students here, but thank you all for being here. My question is a follow-up to the other - the last two audience questions. They were talking about the future. What about in the past? In every city in - every major city in Arizona, you find a dried-up, once largely flowing riverbed, and that's got to have affected the flora and fauna. What have you seen in your research that can tell us what species did and did not exist just 100 or 200 years ago?

FLATOW: I've got about 30 seconds for that answer.

HULTINE: You know, that's a really good point. Around the major streams you had these riparian systems where you had, for instance, large cottonwood trees that occurred. They've disappeared many years ago, and I - without intensive restoration and re-watering of these systems, those really unique gallery forests will not be returning.

DAVIS: I would say go visit the San Pedro River existing riparian area, and you can sort of contrast what we have.

FLATOW: Gentlemen, thank you all very much for a very interesting discussion. Kevin Hultine, a plant physiologist at the Desert Botanical Garden, Ferran Garcia-Pichel, microbiologist and dean of natural sciences, a professor at Arizona State University in Tempe, and Jon Davis, environmental physiologist and course manager for biology at ASU downtown Phoenix campus. Thank you all for coming.

We're going to take a break. When we come back, we're going to look at cosmic collisions, including one that might happen on Mars. Transcript provided by NPR, Copyright NPR.