March 12, 2024 • 40 mins
We are creatures of the epigean world: the world of light on Earth’s surface. But there is another world – a world beneath the surface. In this episode of Stuff to Blow Your Mind, Robert and Joe venture into the world of cave biology or biospeleology. (part 3 of 4)
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Speaker 1 (00:03):
Welcome to Stuff to Blow Your Mind production of iHeartRadio.
Speaker 2 (00:12):
Hey you welcome to Stuff to Blow Your Mind. My
name is Robert Lamb.
Speaker 3 (00:15):
And I am Joe McCormick, and we're back with part
three of our series on cave biology and cave environments.
Let's see what did we talk about in the last
two episodes of the series. Obviously, if you haven't listened
to those already, maybe you should go back and check
those out first, But if you'd rather just jump in here,
that's okay too. In the previous parts, we talked about
(00:36):
some of the common characteristics of cave environments and especially
in ways that would affect animal life. We talked about
the presence of guano in some caves, bat dropping guano
as sort of the base of a food chain, the
equivalent of sunlight to the outside world to the inside
of the cave. And we also talked about some specific
(00:58):
cave organism, such as the blind Mexican cavefish, about which
there has been a lot of research research on how
exactly these fish evolve. These various populations of fish in
northeastern Mexican caves evolved to lose their sight and lose
the pigment in their flesh and so forth. Why that
evolutionary pathway takes place in the cave environment and so forth.
Speaker 2 (01:22):
Yeah, so we're so we've established to a degree, the
cave environment, the cave ecosystem. We've talked about characteristics, We've
talked about some individual species, and we're going to kind
of continue that trend here. We're going to talk about
some more specific organisms that make their homes in the
cave environment, or we're going to look at creatures that
(01:46):
dip into that ecosystem, dip into that biomass that is
already living in the cave.
Speaker 3 (01:52):
All right, well, I think I'm going to kick things
off today with a full cave entry.
Speaker 2 (01:57):
All right, let's do it.
Speaker 3 (01:59):
No, no halfway on this one.
Speaker 2 (02:01):
An obligate cave dweller.
Speaker 3 (02:03):
Right, So, according to one source I was reading, actually
this has been claimed as the first animal to be
recognized as permanently adapted to a cave environment. I couldn't
verify that priority, but that's the claim at least, so
that may be true. This animal is an aquatic cave
salamander called the oulm, also known as the proteus scientific
(02:27):
name Proteus. I think you would say Anguinus proteus a
n g ui in us. The oulm occupies underground waterways
in Europe, especially Kars caves of the Dynaric Mountains, which
is the region of the Balkans along the eastern coast
(02:48):
of the Adriatic Sea, so you can think east of Italy,
across the Adriatic from Italy. And I was looking around
for some good sources on the history of human knowledge
of this animal, because I know the first writings about
it were very interesting. And I came across a paper
in the Journal of Cave and Karst Studies from twenty
twenty one by Evo Lucik called an underworld tailored to tourists,
(03:11):
a dragon, a photomodel, and a bioindicator. And Lucik does
an interesting thing in this article. It's not really focused
on biology. Instead, he's sort of focused on the history
of how this animal has been perceived and categorized by
the media and the public. So the earliest writings about
the ulm are sort of famous. There is an account
(03:32):
in the writing of a seventeenth century author and natural
historian named Johann Weikard von valvasor VLVASR. Valvasor, who was
from the region then known as Carneola what is today Slovenia,
and Valvasor famously published a sort of encyclopedia of the
(03:54):
region known as The Glory of the Duchy of Carniola,
and because of the sting geology of this region with
the kars the caves, the work did contain some investigations
of the local its caves, its associated culture and life.
So Here, summarizing Valvasor, Lucik says that around sixteen eighty nine,
(04:16):
Valvasour reported that he had heard stories from peasants in
a region known as the Vernica that they had seen
a baby dragon in the local water source known as
the Bayliss Spring, and the people who knew this spring
said that the water would flow from it reliably twice
a day, once around midnight and once again around nine am,
(04:39):
and this apparently was linked to some kind of belief
in an underground dragon, which, when it became angry, would
spit out water and perhaps one of its own young
One of the peasants that Valvasore spoke to said he
had seen three young dragons spit up in this way
by the spring, and a local male care claimed that
(05:01):
at one point he took one of the baby dragons
home with him and it was about as big as
his hand and looked like a lizard.
Speaker 2 (05:08):
And it does sort of look like a lizard, but
I would say a little bit lizard, a little bit
vampire princess, a little bit just you know, it depends
what the lightings like. But yeah, it's this long, slender
organism with this elongated head and these wonderfully dainty little limbs.
Speaker 3 (05:28):
Yeah, so it is a salamanderin form. It has a
kind of flat, almost elongated I was gonna say shovel
shaped head, but it's not really shovel shaped. It's more
kind of if you look down from above, the head
is sort of crocodile head shaped. But yeah, it is
a kind of flat head. It has frilly red gills
extending out from the base of its head around its neck.
(05:51):
It has yeah, as you say, delicate little limbs that
don't look like you know, they would do a whole lot,
but it can use them. And otherwise the body is
like a long kind of white snake. It is a translucent, white,
fleshy skin going in the snakelike shape. I've heard some
authors say that if you look at it closely, you
(06:11):
can actually sort of see its organs through its skin
that like the light can sort of penetrate it, and
you can see its insides. And you can look up
pictures of the ulm online. They're they're pretty readily accessible.
It's it's a creepy looking organism. I mean, it does
in some of these photos it almost seems to kind
of glow because I guess of the maybe low light
(06:33):
conditions in which it is being photographed, and its very
pale skin is like reflecting a lot of light.
Speaker 2 (06:40):
Yeah, I mean, I guess, kind of creepy, but also
just haunting, almost kind of elfin in its in its appearance,
you know, like this is a being from another world
and it's its body and form, it's is entirely alien
to us.
Speaker 3 (06:54):
And it's funny. So the rest of this paper by
Lucik really emphasizes the to which sort of mythological themes
have permeated the public understanding of this creature and are
even in some ways still prevalent because of the ways
that this creature is marketed by the local cave systems
(07:16):
as a tourist attraction, and those that marketing places a
lot of emphasis on mythological themes, like referring to it
as a dragon. However, of course, over the following generations
after valvasor, a scientific view of this creature began to
take shape. That it was not a dragon, of course,
but an amphibian, an amphibian that lived in waterways underneath
(07:39):
the earth, which could explain why specimens were sometimes disgorged
from a spring or cave opening after heavy rains. And
so I wanted to get a scientific perspective on this creature,
and I dug up a paper that I thought was interesting.
This was a paper published in the Journal of Zoology
in twenty twenty by belaws, l, Warn and Hurts called
(08:00):
extreme site fidelity of the oulm Proteus anguinus revealed by
a long term capture mark recapture study. So I'm going
to try to do a bit of a recap of
what this paper does in reviewing some of the main
biological characteristics of this animal and then discuss the findings
of their specific experiment. One thing they do, and this
(08:22):
is important to do, I think in the episodes of
this series is they remind us about the common characteristics
of cave habitats. There can be some variation between different caves,
but cave ecosystems are usually going to be shaped by
a reduction or total absence of light that changes a
lot about how organisms survive food scarcity. This is common
(08:44):
to a lot of caves because, as you might recall
other organisms we talked about, like the blind Mexican cavefish,
seem to have adapted to their environment by having lower
nutritional or energy needs than their surface surface variant cousins.
That they need less food to survive, and they have
to adapt to be this way because there's less food
(09:06):
in a cave. Another thing the authors identify is what
they call simplified communities. I looked this up to make
sure I was understanding it right, so I found one
other paper discussing this concept in the journal Bioscience, and
according to their definition, simplification seems to be a quote
reduction in niche diversity. So I think that means you know,
(09:26):
fewer ways for organisms to specialize, which kind of makes
sense within a cave. And then finally they mention that
the cave environments are usually shaped by the fact that
there the cave environment is a major buffer against changes
in climate and other environmental variations. So living in a
deep cave largely removes the variation of things like the
(09:50):
night day cycle, seasonal changes to weather, and so forth.
So a cave environment, though some changes can still come.
And obviously if you're living in an under ground waterway,
like changes in water flow are possible, like heavy rains
could still cause you know, increasing currents in the in
the waterway and so forth. But there are going to
(10:11):
be fewer cyclical, seasonal day, night, and other environmental changes
in a cave than there are outside.
Speaker 2 (10:19):
You mean, of course, you also might want to throw
in seasonal habitation by certain organisms such as bats or
historically things like a cave bear. But even then, the
deeper into the cave you get, you could potentially be
even further removed from the influence of sad.
Speaker 3 (10:37):
Organisms, right, And so the authors say, as several authors
we've looked at have mentioned this, that the evolutionary ecology
of caves is kind of hard to study for maybe
obvious reasons, like aquatic caves especially are kind of hard
to access, they require difficult diving and so forth. And
they say that in the continent of Europe, vertebrates that
(10:58):
are fully adapted to cave life are actually somewhat rare.
There are more species that might go in and out
of caves, but the ones that are the full on troglobions,
the fully adapted to cave organisms that there are not
a whole lot of those. But one of the best
known exceptions is the ome. It is not only a
(11:18):
fully cave adapted organism, it is the largest cave dwelling
vertebrate on Earth. The authors cite a couple of studies
from boulog in nineteen ninety four and Tronte in two
thousand and seven to suggest that the ancestors of the
OLM probably colonized caves somewhere between eight point eight and
(11:39):
twenty million years ago. All known populations except for one,
have regressed eyes and lack pigment in their bodies, so
they appear eyeless and pale or translucent. The one accepted
population is in a cave system in southeast Slovenia.
Speaker 2 (11:58):
There's one called the black Ole. I remember running across,
and it stuck with me because that sounds like such
a like a death metal home in your European caverns.
Speaker 3 (12:09):
But apparently just the difference is for some reason, this
is the one population that has retained its pigment within
the caves. They are top predators, which is kind of
funny because when you look at them, they don't look
like top predators. They look kind of unassuming, maybe creepy,
but you know, they don't look scary. If that distinction
makes sense.
Speaker 2 (12:29):
Yeah, I guess it comes down to again, how scary
do you have to be in order to be the
top predator in a cave ecosystem where again, you have
you do have food chain, you do have a certain
amount of biomass available, but it is it is, it's
all nache. It's reduced, so you're not going to have
(12:50):
these enormous organisms. You know, everything's going to be on
a smaller, hungrier, and more versatile scale.
Speaker 3 (12:56):
Yeah, totally. And to be clear, I mean I'm not
saying I actually think scariness is a biological indicator of
whether you're a top predator or not. But you know,
it's just the intuitions they don't seem to match. But
they are the top predator in their cave environments. They
prey on small animals like cave shrimp, snails, little insects,
and they have no natural predators of their own, so
(13:18):
there's nothing they have to normally watch out for preying
on them. They're the top of the pyramid because they
have no predators. There's a part later in this paper
where the authors observe that the olm do not seem
to engage in hiding behaviors that they observed. At least
they said, it's possible that some olms are like hide
back in cracks and crevices that they were never able
(13:41):
to access on their dives, so you know, they couldn't
locate them back there. But the ones they saw float
out in the open, maintaining their place within the current
of the cave waterway, Like you know, they're just not
worried about that. They don't have to go hide. Now,
another way in which our naive intuitions about what it
means to be a top predator and be violated. You
(14:01):
might hear top predator and you think voracious appetite. You know,
they're eating a lot, eating everything around them. No, Actually,
the ole is famous for having an incredibly incredibly elastic
energy needs, Like it can survive years apparently without food
and can avoid starvation, so it can go into very
(14:22):
low energy mode, can maintain a low metabolism and can
go for a long time without food.
Speaker 2 (14:29):
Yeah, yeah, because again the reduced availability of prey and
a given environment, you need to be able to really
stretch out those the spaces between meal times.
Speaker 3 (14:39):
It's noted that they are neotonic, meaning they retain juvenile
features into adulthood, and there's some other salamander species that
do this as well. They can tolerate water with very
little dissolved oxygen in it, so they have low food
energy needs and low oxygen needs. And while they are
blind to light, they do have a number of compensating
(15:02):
sense mechanisms. The authors mention one of them is what's
known as raeotaxis. Raeotaxis is the ability to sense the
direction of flow within the water, and then that's also
paired with a behavioral instinct that causes the salamander to
turn to orient its body facing into the water flow,
(15:24):
and this is a common way for fish and other
aquatic organisms to remain stationary rather than drifting away with
water currents. They also use other senses than site. They
have underwater hearing, they use their sense of smell or oldfaction,
and they appear to have a magnetic sensoryability as well,
which may help them orient with respect to Earth's magnetic field,
(15:47):
possibly useful for orientation and navigation. As I said, the
ulm has very restricted food needs like some other troglobiants
we've discussed. You remember the blind Mexican cave fish had
very low food needs compared to its surface variant cousin.
They have what the authors call extreme life history adaptations,
(16:08):
meaning their life just appears to sort of sort of
go in slow motion compared to salamanders you might find
on the surface. So I was looking up the maximum
life span of surface amphibians, and of course that varies,
but you know, on average it's going to be more
in the range of ten to twenty years. For large
amphibians that live on the surface. The olem is thought
(16:31):
to live for one hundred years or more, with females
only reproducing once every twelve and a half years roughly.
So that is incredibly long life for an amphibian, incredibly
long in between mating and reproduction. So this experiment tried
to study the behavior of the olm, especially the movement
(16:52):
and migratory patterns of the olm, by using a capture
mark and recapture method. So you know, they catch one,
they mark it, and then they would come back and
see if they could capture the same ones again later,
note where they were relative to the original capture and
so forth. Specifically, they were studying an eastern Herzegovinian population
(17:13):
and the authors found what they called extreme site fidelity.
Most of the creatures that they captured had barely moved
since the years before. The average distance was about five
meters from the original capture location a year before. And
they also did multiple interval studies, so like capturing them
(17:34):
at different times and then checking up on them again.
They found that moving distance was not correlated with the
time since capture. So for a lot of species, you
might expect that the longer you go in between captures,
the farther away from their original location they might have moved.
In these salamanders, not the case. The longer you go
(17:55):
in between captures, it does not, on average effect how
far away they are from the first time. So the
question is why do they move so little? There could
be a number of answers here, and the authors say
to be fair extreme site fidelity, the extreme site fidelity
of these salamanders is not necessarily extreme among amphibians. There
(18:17):
are also some surface amphibians that may have very limited
movement ranges. The authors could not find any reason based
on the environment itself that would limit movement. In other words,
there were no gaps in the movement patterns that would
indicate environmental features they were trying to avoid, And so
they say their best guess is that this hyper sedentary
(18:39):
lifestyle is probably related to energy constraints. The author's right quote.
We can only speculate that animals feeding on a very
low food supply and as consequence, resistant to starvation, reproducing sporadically. Again,
females reproducing on average only once in twelve point five
years and living for a cinch, are very energy cautious
(19:02):
and limit their movements to the minimum. It's a different
kind of animal life to imagine, isn't it like an
animal that to be clear, it's not incapable of moving quickly,
like if you try to capture one and it has
to perform an evasive maneuver, essentially like it's trying to
get away from you. They can move quickly. It just
seems like undisturbed in their natural environment. If you use
(19:27):
the capture recapture method, they haven't moved much after a year,
after two years and so on.
Speaker 2 (19:33):
Wow.
Speaker 3 (19:33):
The author is also note I thought this was interesting
that I don't know exactly what to make of it,
but they say that they have never seen a dead individual.
Kind of interesting.
Speaker 2 (19:42):
H Yeah. I mean, obviously we're dealing with creatures that are,
like we said, difficult to observe anyway, and you know,
we can't count out various other organisms that then scavenge
a dead one. We also have to take into account,
you know, the movements of the waters that have at
least historically been attributed to ones occasionally washing out and
so forth. And even if one didn't wash out all
(20:06):
the way to where humans could have observed them, it
might wash them out to where other organisms would have
a shot at scavenging them. But still it's an interesting tidbit.
Speaker 3 (20:17):
Yeah, yeah, yeah. To be clear, I don't think they
meant like humans have never observed a dead one obviously.
I think they mean like in the in the region
where they're looking at the live ones, they've never seen
a dead one there, right right, yeah.
Speaker 2 (20:29):
Yeah, And like I said, that could be because it
is they do get periodically fleshed out, I'm guessing, or yeah,
scavengers of one sort or another.
Speaker 3 (20:37):
The author is add a conservation note in their paper,
which is that the extreme site fidelity of the of
the olm makes it quite vulnerable to water pollution. You know,
it changes to water quality, especially like if it can't
I think, if it can't really migrate very effectively to
get to a place where there's better water, it's more
vulnerable to changes in water quality locally. Though. Vulnerability to
(21:01):
water pollution I think is also true of many surface amphibians,
who are especially vulnerable because of the permeability of their skin.
So yeah, another reason why, I mean, not like we
needed that. Many more reasons why water pollution is a
bad thing. But here's another one. But final note, if
you haven't seen a picture of the ulm, you should
look this one up. You want to see this flesh.
Speaker 2 (21:22):
Oh yeah, absolutely, it's a very it's.
Speaker 3 (21:24):
A very Cronenberg biodesign.
Speaker 2 (21:28):
Yeah, they're like I say, they're a little creepy, a
little cute. They're very unique. All right. I want to
get into a topic here that that came up early
on in my research and a paper that came up
(21:50):
pretty early on in researching these episodes, and it has
to do with intra gilled predation, that's the killing and
eating of potential competitors with any ecosystem, which is apparently
a pretty big deal in the food chain of the
Hypogean world. So, as we discussed in previous episodes and
specifically in the last episode, you know, bat guano is
(22:11):
kind of an alternative sunlight that forms sort of the
base of the subterrane and ecosystem a lot of the
times as bats roost in the cave and defecate, thus
bringing new resources for various organisms to feed on, which
in turn feed other consumers. And as discussed in a
twenty twenty one paper published in Scientific Reports by param
(22:31):
Mutchova at all quote the food web in a subterranean
ecosystem is driven by introgild predation. So in this paper
they drive home some of what we discussed last time
that quote, detrit us based food webs are prevalent in
cave systems. Though you do have cases where again sunlight
enters cavern openings or through other fissures, and also have
(22:55):
situations where some manner of chemo autotrophy is taking place,
but still, you know, it often falls to back guano
as well as other transportation networks for dead plants, and
to try it as such as the gravitation pawn or streams.
It's like a like a steep sinkhole situation percolating water.
(23:17):
And also animal cadavers, the animal cadaver being something that is,
you know, the animal has gone in there and died
or something has brought the animal couldaver into the cave generally.
Speaker 3 (23:27):
So that's a good list. So, as you said, there
are places where the sunlight it's in chemo autotrophy would
be an alternative to photo autotrophy. You know, mostly we're
on the on the surface. The autotrophs are making energy
out of sunlight, but it can also be done with
certain types of chemicals in the darkness. And then as
(23:47):
you said, back guano, and then just basically various ways
for stuff to fall into the cave or be brought
into the cave that could.
Speaker 2 (23:54):
Be eaten, Yeah, falling in and potentially flowing in in
the same way that a dead own might flow out
of a cave, if we're to take that earlier account
at face value. So anyway, that's the base, and you
have all of these consumer interactions atop of all that.
In a cave, and this particular study examined the subterranean
(24:15):
ecosystem of the Autovaska Cave in Slovakia. The predators they
examined were all arthropods living in the cave, including a
species of might a beetle, two different spiders, and a
couple of other species, and they were able to examine
DNA in the guts of each species to see what
(24:35):
they were eating. As expected, they found a complex system
of intragil predation again killing and eating of potential competitors.
And they included a handy visual guide that I really liked,
so I included it here for you to look at, Joe.
They have essentially five dots scored here on the illustration,
(24:56):
each one representing one of these five species they looked at.
In each one is color coded with color coded lines
indicating which one feeds on which, and you end up
with this complex almost pretty much a star pattern, but
with a few more lines on some connections, and sometimes
there's not a line connecting one species to another.
Speaker 3 (25:17):
It looks like almost all of them are eating each other.
There's one that's really eating everybody and almost and all
the others are eating at least two other ones.
Speaker 2 (25:28):
Right, right, And then you know they acknowledge their limitations
and their study and so forth, so it's not this
is not necessarily all that ever happens between these these species,
but this is what they're they're got syndicated when they
were studied, and so they stress that intragil predation is
often important in nitrogen poor diets, as is cannibalism, which
(25:52):
that which they found evidence of, and it should be
stressed that scavenging may be part of both cases. So
you know, on one hand, you have like straight up
predation like well there's my competitor, I've got the drop
on them. I shall eat them, but also a situation
of well there is my competitor, they have died.
Speaker 3 (26:10):
What you're going to do, right, yeah, because often in
energy relationships like this, trying to prey on a healthy
adult of like a of a competitor within the food
chain is usually going to be kind of dangerous. So
I think we've read about integuild predation before, some of
(26:30):
it being not predation but scavenging, but other ones being
like adults of one species preying on the young of
the other.
Speaker 2 (26:38):
Yeah, because you know, otherwise going toe to toe with
someone or something in the ecosystem that is your equal, Like,
that's that's a gamble, and survival is on the line
regardless if you engage in that struggle, And you might
only engage in that struggle if survival is already on
the line. And yeah, in the impoverished food web of
(27:01):
the dark, you get what you get. You don't pitch
a fit. Each of the species here that they looked
at consumed a wide variety of prey and indulged in
integral predation as presumably necessary. So it would seem, based
on what I was reading here that Yeah, while you know,
integral predation of course, as you said, occurs in the
sunlit world as well, and in the oceans and so forth,
(27:25):
within the cave environment, it might be more pronounced again
due to the limited scope of the available biomass, available
nutrients and so forth.
Speaker 3 (27:35):
Right, Yeah, I mean, the fact that it's a place
where food is scarce creates weird biological incentives and emphasies.
Speaker 2 (27:42):
Yeah. So yeah, I thought this was very interesting. But
I want to get into this other area here for
the remainder of the episode here having to do with
outsiders in the cave, creatures who have come into the
cave to take advantage of what is there. Because once again,
and there's the there, the there's the idea that the
cave environment comes with pros and cons. One con as
(28:05):
we as we've discussed already, is that the food chain
here is just less robust, uh specialized, obligate. Cave organisms
generally have carved out a very narrow niche in which
to live. A big pro, however, is, as with the OLM,
you're often dealing with fewer predators and a more secluded life.
Speaker 3 (28:24):
Mm hmm.
Speaker 2 (28:25):
It's like the Phantom of the Opera. You know, you
have this vast catacomb empire over which to rule and
row your boat around, and you have great acoustics, you know,
for your singing, for your your your cool pipe organ.
But the real music scene is upstairs in the sunlit world,
and you are, you know, to a large extent cut
off from that.
Speaker 3 (28:44):
You really need to kidnap a singer from up there
to to make your make your songs work better down there. Yeah.
Speaker 2 (28:51):
Yeah, So there there is a potential advantage here for
creatures of both worlds and creatures of the surface that
have figured out how and when to venture into caves
to take advantage of the creatures that live there, at
least live there periodically. And you know, I don't think
(29:11):
we've run across anything that's going in to harvest the olms.
But as we've been discussing one of the most abundant
life forms you might pray or scavenge upon the in
caverns are creatures that spend part of their time there
as well. That being bats, they roost in great numbers.
They enjoy a great deal of security there. But a
(29:33):
specialist could get in there and reap the bounties.
Speaker 3 (29:37):
Oh, I don't know if I ever thought about that.
So what would do that?
Speaker 2 (29:41):
Well, a number of organisms. Actually, I was looking at
a paper from nineteen seventy two. This is by Winkler
and Atoms titled utilization of Southwestern Bat Caves by Terrestrial Carnivores,
and this is published in the Journal of the American
Middland Naturalist. And they put out that various predators venture
into caves to enjoy the occasional bat feast, either via
(30:02):
active hunting or by scavenging for fallen bats. And this
includes broadly like various reptiles, raptorial birds, and mammals. For instance,
they point out that at Bracken Cave, raccoons and some
skunks were observed to venture into the cave to prey
on fallen bats at the cave mouth. Because you know,
(30:25):
I think we discussed this at least in passing earlier.
You have large populations of bats residing in many of
these caves, and occasionally bats do fall be they you know,
young bats, older bats, in firm bats, et cetera. They're
just too many of them this for this not to happen.
(30:45):
It will occasionally rain a little bit of food in
the form of a bat, and an organism that is
operated into tunistic enough can get in there and collect
those and eat them, or you know, eat them before
they're able to crawl across the cave floor and then
back up the walls to enjoy their roost again.
Speaker 3 (31:04):
So the cave buffet underneath the bat roost is mostly guano,
but occasionally bat meat as well.
Speaker 2 (31:10):
That's right. So ringtail cats were observed at another cave,
but it seemed as if, especially at Bracken Cave, raccoons
were the most likely to take advantage of the bat
bounty during both the day and the night. And in
you know, this this makes sense concerning the raccoon, because,
as we've talked about in the show before, you know,
(31:32):
they're they're great opportunists. Uh, they are. They're nocturnal omnivores,
and they have exceedingly wise pause.
Speaker 3 (31:41):
Oh that's right. I'm just now recalling that we did
an episode a while back about their apparent their strange
apparent washing of food behavior and the question about like
whether that really is washing or some other type of
behavioral instinct. And oh, I can't remember off the top
of my head what episode that was in, but I
remember that that that one really got my mind going.
Speaker 2 (32:01):
Yeah, I remember talking about like, for instance, they are
they are they're great opportunistic organisms that can adapt to
various environments. So they've done quite well with urban environments.
Uh and uh and yeah. We also discussed the heartbreaking
video footage that you can look up online of a
raccoon attempting to to dunk it's uh it's a plunder
(32:24):
of cotton candy into the water, and then seemingly confused
as it draws the bounty back out of the water
and finds that it is no longer uh there for it.
It's again kind of heartbreaking to.
Speaker 3 (32:37):
Watch yeah, totally. I just looked it up. By the way,
it was in our series on animals, quote cooking things
on the cuisine and kitchen behaviors observed in animals, including
the apparent washing of food. But again, I think there
was a question of whether that's really what raccoons are
doing or not.
Speaker 2 (32:55):
Yeah, but they're they're they're they're little paws, they are
little hands. If you will are are are excellent. I've
seen it described that they can essentially see with their
hands in ways that we could maybe relate to on
some level, But as is often the case with the
sense worlds of animals, of non human animals, we generally
(33:15):
can't fully imagine what it's like. Like they can see
with their hands is the best way that we can
perhaps understand it.
Speaker 3 (33:23):
Yeah, yeah, that was one of the hypotheses. It was
like that the water somehow hypercharges the sensitivity of the
hands and sensing the food. Yeah.
Speaker 2 (33:32):
Yeah. Now this cave in question, Bracken Cave. This is
a Texas cave outside of San Antonio that is home
to the largest known bat colony in the world. Some
twenty million Mexican free tail bats roost here between March
and October. This also apparently makes it the largest known
concentration of mammals period, including humans. I'm assuming, and I
(33:56):
imagine this takes into account the size of the cave
and the estimation estimated concentration of bats as compared to
human cities. But even among human cities, there are only
something like six cities with populations of more than twenty million.
So we're talking a lot of bats. And I didn't run,
I didn't look up or do the math on this,
but you know, you think about twenty million bats, how
(34:17):
many bats are going to potentially fall? So that does
create a certain opportunity for animals that are willing to
get in there day or night and pick them off
before they can get back up to the top.
Speaker 3 (34:29):
Yeah, with twenty million bats, I mean, even if you
assume a low death rate, that's got to be thousands
falling into the floor all the time.
Speaker 2 (34:36):
Yeah. Now, reptiles also get on in the action as well,
as that paper indicated, And one of the more alarming examples,
I don't know, it could be alarming, depends on what
you think about snakes is the example of yellow red
rat snakes found in a cave in Mexico that is
sometimes referred to as the Cave of Hanging Snakes.
Speaker 3 (34:58):
Hanging snakes.
Speaker 2 (34:59):
Yes, so, the yellow red rat snake is endemic to
Mexico and Central America, so it's fairly widespread. It's non venomous.
It prays mostly on rodents and birds and lizards, but
also on the menu are bats. So the Mexican cave
in question is Cantemo Cave in the Mexican state of
(35:22):
kintani Roo, about one hundred and eighty miles from Cancun,
known locally just as the bat Cave. According to Jose
Maria Morells, writing for Atlas Obscura, the snakes here have
developed an amazing method of eating those bats that doesn't
involve picking them off on the cave floor. So what
(35:46):
they do, apparently, is they crawl up into the cracks
in the ceiling of the cave as well as high
up on the cave walls. And then when the bats,
you know, the bats are roosting in there, so they
leave and then they come back. They leave to feed,
and then they come back. And when they're doing this,
when they're going in or out of the cave, that
(36:07):
is when the snakes will either dangle down or otherwise
like lash out to catch a passing bat in its mouth.
Speaker 3 (36:15):
Wow.
Speaker 2 (36:17):
And I've included a couple of photos here for you
to look at, Joe, one of the snake grabbing having
grabbed a bat and it's like, you know, just swallowing it.
And then there's another one of the snake up in
the recesses. This is these are actually, these are excellent photos.
They're from a Newsweek article that put that that profiled
these snakes.
Speaker 3 (36:37):
That is crazy. Now, I had a question that I
think I may have partially answered, but I just looked
up more images of these snakes jumping out to snag bats,
and my question was, well, how do they have the
leverage to do that? Because I was imagining them just
sort of like crawling up a cave wall. But in
some of the pictures I'm looking at, they have found
(36:58):
like a they're in like a recess, like a cubby
hole in the wall, and so I think they're gripping
something back there with the back half of their body
where they while they lunge out with the front half
to to grab a bat.
Speaker 2 (37:09):
Now you mentioned looking up images of this, Yeah, there
there are a lot of images of these of these snakes.
There's some footage as well. This cave has become an
ecotourism destination, so a lot of people have gotten to
go there. It's been covered in a lot of by
a lot of news outlets, various documentaries, so you can
definitely see some images of these snakes either you know,
dangling from the ceiling or consuming the bats that they
(37:32):
have acquired.
Speaker 3 (37:34):
Wow, that's one of those behaviors where it's like, I
would love an evolutionary account of how that arises, if
that's known, or if there's something suspected, like like how
long have these snakes specialized in attacking bats this way?
And like what were they doing before that?
Speaker 2 (37:51):
Yeah? Yeah, I mean I guess it's kind of a
natural extrapolation of surface world environments, especially thinking our boreal environments, right. Yeah,
the cave is just like a novel form of that.
And with the bat population, you have just such a
concentration of potential prey. You're going to have organisms that
(38:12):
are drawn to it and ones that are able to
adapt their existing practices, their existing predation and scavenging practices
to it, or as with the raccoon, are just generally
great opportunists. You know they're going to be able to
help reap some of that bounty for themselves.
Speaker 3 (38:29):
Well, Rob, thank you for introducing me to these hanging snakes.
I didn't know they existed, and now I love them.
So I think we probably have to call it there
for part three of our series on cave biology, but
I think we're going to be back for one more.
Three was not enough. There will be one more episode.
Speaker 2 (38:45):
I think, so. I think a fourth episode will wrap
it up for this journey into the caves, but you know,
after that, we'll probably be back in the future at
some point or another. Caves and their ecosystems and human
traditions associated with them are just too fascinating, all right.
In the meantime, we're going to go ahead and remind
everybody that's stuff to blow your mind. Is primarily a
science and culture podcast that publishes new core episodes on
(39:07):
Tuesdays and Thursdays, Sandwiched in between there on Wednesdays, there's
a short form episode for you monster fact Artifact, or
Anamalia stipendium. On Mondays we do listener mail, and then
on Fridays we set aside most serious concerns to just
talk about a weird film on Weird House Cinema. Usually
those are self contained single episodes, but if you're just
(39:28):
tuning into our channel for the first time, this week,
we are covering David Lynch's nineteen eighty four adaptation of
Dune in two parts, because it is that weird, that
packed with talent, and also, you know, Dune is in
the air right now, the spice is in the air
and we have to acknowledge that.
Speaker 3 (39:46):
Cool wahad Huge thanks as always to our excellent audio
producer JJ Posway. If you would like to get in
touch with us with feedback on this episode or any other,
to suggest a topic for the future, or just to
say hello, you can email us at contact at stuff
to Blow your Mind dot com.
Speaker 1 (40:11):
Stuff to Blow Your Mind is production of iHeartRadio. For
more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts,
or wherever you're listening to your favorite shows.
Welcome to Stuff to Blow Your Mind production of iHeartRadio.
Speaker 2 (00:12):
Hey you welcome to Stuff to Blow Your Mind. My
name is Robert Lamb.
Speaker 3 (00:15):
And I am Joe McCormick, and we're back with part
three of our series on cave biology and cave environments.
Let's see what did we talk about in the last
two episodes of the series. Obviously, if you haven't listened
to those already, maybe you should go back and check
those out first, But if you'd rather just jump in here,
that's okay too. In the previous parts, we talked about
(00:36):
some of the common characteristics of cave environments and especially
in ways that would affect animal life. We talked about
the presence of guano in some caves, bat dropping guano
as sort of the base of a food chain, the
equivalent of sunlight to the outside world to the inside
of the cave. And we also talked about some specific
(00:58):
cave organism, such as the blind Mexican cavefish, about which
there has been a lot of research research on how
exactly these fish evolve. These various populations of fish in
northeastern Mexican caves evolved to lose their sight and lose
the pigment in their flesh and so forth. Why that
evolutionary pathway takes place in the cave environment and so forth.
Speaker 2 (01:22):
Yeah, so we're so we've established to a degree, the
cave environment, the cave ecosystem. We've talked about characteristics, We've
talked about some individual species, and we're going to kind
of continue that trend here. We're going to talk about
some more specific organisms that make their homes in the
cave environment, or we're going to look at creatures that
(01:46):
dip into that ecosystem, dip into that biomass that is
already living in the cave.
Speaker 3 (01:52):
All right, well, I think I'm going to kick things
off today with a full cave entry.
Speaker 2 (01:57):
All right, let's do it.
Speaker 3 (01:59):
No, no halfway on this one.
Speaker 2 (02:01):
An obligate cave dweller.
Speaker 3 (02:03):
Right, So, according to one source I was reading, actually
this has been claimed as the first animal to be
recognized as permanently adapted to a cave environment. I couldn't
verify that priority, but that's the claim at least, so
that may be true. This animal is an aquatic cave
salamander called the oulm, also known as the proteus scientific
(02:27):
name Proteus. I think you would say Anguinus proteus a
n g ui in us. The oulm occupies underground waterways
in Europe, especially Kars caves of the Dynaric Mountains, which
is the region of the Balkans along the eastern coast
(02:48):
of the Adriatic Sea, so you can think east of Italy,
across the Adriatic from Italy. And I was looking around
for some good sources on the history of human knowledge
of this animal, because I know the first writings about
it were very interesting. And I came across a paper
in the Journal of Cave and Karst Studies from twenty
twenty one by Evo Lucik called an underworld tailored to tourists,
(03:11):
a dragon, a photomodel, and a bioindicator. And Lucik does
an interesting thing in this article. It's not really focused
on biology. Instead, he's sort of focused on the history
of how this animal has been perceived and categorized by
the media and the public. So the earliest writings about
the ulm are sort of famous. There is an account
(03:32):
in the writing of a seventeenth century author and natural
historian named Johann Weikard von valvasor VLVASR. Valvasor, who was
from the region then known as Carneola what is today Slovenia,
and Valvasor famously published a sort of encyclopedia of the
(03:54):
region known as The Glory of the Duchy of Carniola,
and because of the sting geology of this region with
the kars the caves, the work did contain some investigations
of the local its caves, its associated culture and life.
So Here, summarizing Valvasor, Lucik says that around sixteen eighty nine,
(04:16):
Valvasour reported that he had heard stories from peasants in
a region known as the Vernica that they had seen
a baby dragon in the local water source known as
the Bayliss Spring, and the people who knew this spring
said that the water would flow from it reliably twice
a day, once around midnight and once again around nine am,
(04:39):
and this apparently was linked to some kind of belief
in an underground dragon, which, when it became angry, would
spit out water and perhaps one of its own young
One of the peasants that Valvasore spoke to said he
had seen three young dragons spit up in this way
by the spring, and a local male care claimed that
(05:01):
at one point he took one of the baby dragons
home with him and it was about as big as
his hand and looked like a lizard.
Speaker 2 (05:08):
And it does sort of look like a lizard, but
I would say a little bit lizard, a little bit
vampire princess, a little bit just you know, it depends
what the lightings like. But yeah, it's this long, slender
organism with this elongated head and these wonderfully dainty little limbs.
Speaker 3 (05:28):
Yeah, so it is a salamanderin form. It has a
kind of flat, almost elongated I was gonna say shovel
shaped head, but it's not really shovel shaped. It's more
kind of if you look down from above, the head
is sort of crocodile head shaped. But yeah, it is
a kind of flat head. It has frilly red gills
extending out from the base of its head around its neck.
(05:51):
It has yeah, as you say, delicate little limbs that
don't look like you know, they would do a whole lot,
but it can use them. And otherwise the body is
like a long kind of white snake. It is a translucent, white,
fleshy skin going in the snakelike shape. I've heard some
authors say that if you look at it closely, you
(06:11):
can actually sort of see its organs through its skin
that like the light can sort of penetrate it, and
you can see its insides. And you can look up
pictures of the ulm online. They're they're pretty readily accessible.
It's it's a creepy looking organism. I mean, it does
in some of these photos it almost seems to kind
of glow because I guess of the maybe low light
(06:33):
conditions in which it is being photographed, and its very
pale skin is like reflecting a lot of light.
Speaker 2 (06:40):
Yeah, I mean, I guess, kind of creepy, but also
just haunting, almost kind of elfin in its in its appearance,
you know, like this is a being from another world
and it's its body and form, it's is entirely alien
to us.
Speaker 3 (06:54):
And it's funny. So the rest of this paper by
Lucik really emphasizes the to which sort of mythological themes
have permeated the public understanding of this creature and are
even in some ways still prevalent because of the ways
that this creature is marketed by the local cave systems
(07:16):
as a tourist attraction, and those that marketing places a
lot of emphasis on mythological themes, like referring to it
as a dragon. However, of course, over the following generations
after valvasor, a scientific view of this creature began to
take shape. That it was not a dragon, of course,
but an amphibian, an amphibian that lived in waterways underneath
(07:39):
the earth, which could explain why specimens were sometimes disgorged
from a spring or cave opening after heavy rains. And
so I wanted to get a scientific perspective on this creature,
and I dug up a paper that I thought was interesting.
This was a paper published in the Journal of Zoology
in twenty twenty by belaws, l, Warn and Hurts called
(08:00):
extreme site fidelity of the oulm Proteus anguinus revealed by
a long term capture mark recapture study. So I'm going
to try to do a bit of a recap of
what this paper does in reviewing some of the main
biological characteristics of this animal and then discuss the findings
of their specific experiment. One thing they do, and this
(08:22):
is important to do, I think in the episodes of
this series is they remind us about the common characteristics
of cave habitats. There can be some variation between different caves,
but cave ecosystems are usually going to be shaped by
a reduction or total absence of light that changes a
lot about how organisms survive food scarcity. This is common
(08:44):
to a lot of caves because, as you might recall
other organisms we talked about, like the blind Mexican cavefish,
seem to have adapted to their environment by having lower
nutritional or energy needs than their surface surface variant cousins.
That they need less food to survive, and they have
to adapt to be this way because there's less food
(09:06):
in a cave. Another thing the authors identify is what
they call simplified communities. I looked this up to make
sure I was understanding it right, so I found one
other paper discussing this concept in the journal Bioscience, and
according to their definition, simplification seems to be a quote
reduction in niche diversity. So I think that means you know,
(09:26):
fewer ways for organisms to specialize, which kind of makes
sense within a cave. And then finally they mention that
the cave environments are usually shaped by the fact that
there the cave environment is a major buffer against changes
in climate and other environmental variations. So living in a
deep cave largely removes the variation of things like the
(09:50):
night day cycle, seasonal changes to weather, and so forth.
So a cave environment, though some changes can still come.
And obviously if you're living in an under ground waterway,
like changes in water flow are possible, like heavy rains
could still cause you know, increasing currents in the in
the waterway and so forth. But there are going to
(10:11):
be fewer cyclical, seasonal day, night, and other environmental changes
in a cave than there are outside.
Speaker 2 (10:19):
You mean, of course, you also might want to throw
in seasonal habitation by certain organisms such as bats or
historically things like a cave bear. But even then, the
deeper into the cave you get, you could potentially be
even further removed from the influence of sad.
Speaker 3 (10:37):
Organisms, right, And so the authors say, as several authors
we've looked at have mentioned this, that the evolutionary ecology
of caves is kind of hard to study for maybe
obvious reasons, like aquatic caves especially are kind of hard
to access, they require difficult diving and so forth. And
they say that in the continent of Europe, vertebrates that
(10:58):
are fully adapted to cave life are actually somewhat rare.
There are more species that might go in and out
of caves, but the ones that are the full on troglobions,
the fully adapted to cave organisms that there are not
a whole lot of those. But one of the best
known exceptions is the ome. It is not only a
(11:18):
fully cave adapted organism, it is the largest cave dwelling
vertebrate on Earth. The authors cite a couple of studies
from boulog in nineteen ninety four and Tronte in two
thousand and seven to suggest that the ancestors of the
OLM probably colonized caves somewhere between eight point eight and
(11:39):
twenty million years ago. All known populations except for one,
have regressed eyes and lack pigment in their bodies, so
they appear eyeless and pale or translucent. The one accepted
population is in a cave system in southeast Slovenia.
Speaker 2 (11:58):
There's one called the black Ole. I remember running across,
and it stuck with me because that sounds like such
a like a death metal home in your European caverns.
Speaker 3 (12:09):
But apparently just the difference is for some reason, this
is the one population that has retained its pigment within
the caves. They are top predators, which is kind of
funny because when you look at them, they don't look
like top predators. They look kind of unassuming, maybe creepy,
but you know, they don't look scary. If that distinction
makes sense.
Speaker 2 (12:29):
Yeah, I guess it comes down to again, how scary
do you have to be in order to be the
top predator in a cave ecosystem where again, you have
you do have food chain, you do have a certain
amount of biomass available, but it is it is, it's
all nache. It's reduced, so you're not going to have
(12:50):
these enormous organisms. You know, everything's going to be on
a smaller, hungrier, and more versatile scale.
Speaker 3 (12:56):
Yeah, totally. And to be clear, I mean I'm not
saying I actually think scariness is a biological indicator of
whether you're a top predator or not. But you know,
it's just the intuitions they don't seem to match. But
they are the top predator in their cave environments. They
prey on small animals like cave shrimp, snails, little insects,
and they have no natural predators of their own, so
(13:18):
there's nothing they have to normally watch out for preying
on them. They're the top of the pyramid because they
have no predators. There's a part later in this paper
where the authors observe that the olm do not seem
to engage in hiding behaviors that they observed. At least
they said, it's possible that some olms are like hide
back in cracks and crevices that they were never able
(13:41):
to access on their dives, so you know, they couldn't
locate them back there. But the ones they saw float
out in the open, maintaining their place within the current
of the cave waterway, Like you know, they're just not
worried about that. They don't have to go hide. Now,
another way in which our naive intuitions about what it
means to be a top predator and be violated. You
(14:01):
might hear top predator and you think voracious appetite. You know,
they're eating a lot, eating everything around them. No, Actually,
the ole is famous for having an incredibly incredibly elastic
energy needs, Like it can survive years apparently without food
and can avoid starvation, so it can go into very
(14:22):
low energy mode, can maintain a low metabolism and can
go for a long time without food.
Speaker 2 (14:29):
Yeah, yeah, because again the reduced availability of prey and
a given environment, you need to be able to really
stretch out those the spaces between meal times.
Speaker 3 (14:39):
It's noted that they are neotonic, meaning they retain juvenile
features into adulthood, and there's some other salamander species that
do this as well. They can tolerate water with very
little dissolved oxygen in it, so they have low food
energy needs and low oxygen needs. And while they are
blind to light, they do have a number of compensating
(15:02):
sense mechanisms. The authors mention one of them is what's
known as raeotaxis. Raeotaxis is the ability to sense the
direction of flow within the water, and then that's also
paired with a behavioral instinct that causes the salamander to
turn to orient its body facing into the water flow,
(15:24):
and this is a common way for fish and other
aquatic organisms to remain stationary rather than drifting away with
water currents. They also use other senses than site. They
have underwater hearing, they use their sense of smell or oldfaction,
and they appear to have a magnetic sensoryability as well,
which may help them orient with respect to Earth's magnetic field,
(15:47):
possibly useful for orientation and navigation. As I said, the
ulm has very restricted food needs like some other troglobiants
we've discussed. You remember the blind Mexican cave fish had
very low food needs compared to its surface variant cousin.
They have what the authors call extreme life history adaptations,
(16:08):
meaning their life just appears to sort of sort of
go in slow motion compared to salamanders you might find
on the surface. So I was looking up the maximum
life span of surface amphibians, and of course that varies,
but you know, on average it's going to be more
in the range of ten to twenty years. For large
amphibians that live on the surface. The olem is thought
(16:31):
to live for one hundred years or more, with females
only reproducing once every twelve and a half years roughly.
So that is incredibly long life for an amphibian, incredibly
long in between mating and reproduction. So this experiment tried
to study the behavior of the olm, especially the movement
(16:52):
and migratory patterns of the olm, by using a capture
mark and recapture method. So you know, they catch one,
they mark it, and then they would come back and
see if they could capture the same ones again later,
note where they were relative to the original capture and
so forth. Specifically, they were studying an eastern Herzegovinian population
(17:13):
and the authors found what they called extreme site fidelity.
Most of the creatures that they captured had barely moved
since the years before. The average distance was about five
meters from the original capture location a year before. And
they also did multiple interval studies, so like capturing them
(17:34):
at different times and then checking up on them again.
They found that moving distance was not correlated with the
time since capture. So for a lot of species, you
might expect that the longer you go in between captures,
the farther away from their original location they might have moved.
In these salamanders, not the case. The longer you go
(17:55):
in between captures, it does not, on average effect how
far away they are from the first time. So the
question is why do they move so little? There could
be a number of answers here, and the authors say
to be fair extreme site fidelity, the extreme site fidelity
of these salamanders is not necessarily extreme among amphibians. There
(18:17):
are also some surface amphibians that may have very limited
movement ranges. The authors could not find any reason based
on the environment itself that would limit movement. In other words,
there were no gaps in the movement patterns that would
indicate environmental features they were trying to avoid, And so
they say their best guess is that this hyper sedentary
(18:39):
lifestyle is probably related to energy constraints. The author's right quote.
We can only speculate that animals feeding on a very
low food supply and as consequence, resistant to starvation, reproducing sporadically. Again,
females reproducing on average only once in twelve point five
years and living for a cinch, are very energy cautious
(19:02):
and limit their movements to the minimum. It's a different
kind of animal life to imagine, isn't it like an
animal that to be clear, it's not incapable of moving quickly,
like if you try to capture one and it has
to perform an evasive maneuver, essentially like it's trying to
get away from you. They can move quickly. It just
seems like undisturbed in their natural environment. If you use
(19:27):
the capture recapture method, they haven't moved much after a year,
after two years and so on.
Speaker 2 (19:33):
Wow.
Speaker 3 (19:33):
The author is also note I thought this was interesting
that I don't know exactly what to make of it,
but they say that they have never seen a dead individual.
Kind of interesting.
Speaker 2 (19:42):
H Yeah. I mean, obviously we're dealing with creatures that are,
like we said, difficult to observe anyway, and you know,
we can't count out various other organisms that then scavenge
a dead one. We also have to take into account,
you know, the movements of the waters that have at
least historically been attributed to ones occasionally washing out and
so forth. And even if one didn't wash out all
(20:06):
the way to where humans could have observed them, it
might wash them out to where other organisms would have
a shot at scavenging them. But still it's an interesting tidbit.
Speaker 3 (20:17):
Yeah, yeah, yeah. To be clear, I don't think they
meant like humans have never observed a dead one obviously.
I think they mean like in the in the region
where they're looking at the live ones, they've never seen
a dead one there, right right, yeah.
Speaker 2 (20:29):
Yeah, And like I said, that could be because it
is they do get periodically fleshed out, I'm guessing, or yeah,
scavengers of one sort or another.
Speaker 3 (20:37):
The author is add a conservation note in their paper,
which is that the extreme site fidelity of the of
the olm makes it quite vulnerable to water pollution. You know,
it changes to water quality, especially like if it can't
I think, if it can't really migrate very effectively to
get to a place where there's better water, it's more
vulnerable to changes in water quality locally. Though. Vulnerability to
(21:01):
water pollution I think is also true of many surface amphibians,
who are especially vulnerable because of the permeability of their skin.
So yeah, another reason why, I mean, not like we
needed that. Many more reasons why water pollution is a
bad thing. But here's another one. But final note, if
you haven't seen a picture of the ulm, you should
look this one up. You want to see this flesh.
Speaker 2 (21:22):
Oh yeah, absolutely, it's a very it's.
Speaker 3 (21:24):
A very Cronenberg biodesign.
Speaker 2 (21:28):
Yeah, they're like I say, they're a little creepy, a
little cute. They're very unique. All right. I want to
get into a topic here that that came up early
on in my research and a paper that came up
(21:50):
pretty early on in researching these episodes, and it has
to do with intra gilled predation, that's the killing and
eating of potential competitors with any ecosystem, which is apparently
a pretty big deal in the food chain of the
Hypogean world. So, as we discussed in previous episodes and
specifically in the last episode, you know, bat guano is
(22:11):
kind of an alternative sunlight that forms sort of the
base of the subterrane and ecosystem a lot of the
times as bats roost in the cave and defecate, thus
bringing new resources for various organisms to feed on, which
in turn feed other consumers. And as discussed in a
twenty twenty one paper published in Scientific Reports by param
(22:31):
Mutchova at all quote the food web in a subterranean
ecosystem is driven by introgild predation. So in this paper
they drive home some of what we discussed last time
that quote, detrit us based food webs are prevalent in
cave systems. Though you do have cases where again sunlight
enters cavern openings or through other fissures, and also have
(22:55):
situations where some manner of chemo autotrophy is taking place,
but still, you know, it often falls to back guano
as well as other transportation networks for dead plants, and
to try it as such as the gravitation pawn or streams.
It's like a like a steep sinkhole situation percolating water.
(23:17):
And also animal cadavers, the animal cadaver being something that is,
you know, the animal has gone in there and died
or something has brought the animal couldaver into the cave generally.
Speaker 3 (23:27):
So that's a good list. So, as you said, there
are places where the sunlight it's in chemo autotrophy would
be an alternative to photo autotrophy. You know, mostly we're
on the on the surface. The autotrophs are making energy
out of sunlight, but it can also be done with
certain types of chemicals in the darkness. And then as
(23:47):
you said, back guano, and then just basically various ways
for stuff to fall into the cave or be brought
into the cave that could.
Speaker 2 (23:54):
Be eaten, Yeah, falling in and potentially flowing in in
the same way that a dead own might flow out
of a cave, if we're to take that earlier account
at face value. So anyway, that's the base, and you
have all of these consumer interactions atop of all that.
In a cave, and this particular study examined the subterranean
(24:15):
ecosystem of the Autovaska Cave in Slovakia. The predators they
examined were all arthropods living in the cave, including a
species of might a beetle, two different spiders, and a
couple of other species, and they were able to examine
DNA in the guts of each species to see what
(24:35):
they were eating. As expected, they found a complex system
of intragil predation again killing and eating of potential competitors.
And they included a handy visual guide that I really liked,
so I included it here for you to look at, Joe.
They have essentially five dots scored here on the illustration,
(24:56):
each one representing one of these five species they looked at.
In each one is color coded with color coded lines
indicating which one feeds on which, and you end up
with this complex almost pretty much a star pattern, but
with a few more lines on some connections, and sometimes
there's not a line connecting one species to another.
Speaker 3 (25:17):
It looks like almost all of them are eating each other.
There's one that's really eating everybody and almost and all
the others are eating at least two other ones.
Speaker 2 (25:28):
Right, right, And then you know they acknowledge their limitations
and their study and so forth, so it's not this
is not necessarily all that ever happens between these these species,
but this is what they're they're got syndicated when they
were studied, and so they stress that intragil predation is
often important in nitrogen poor diets, as is cannibalism, which
(25:52):
that which they found evidence of, and it should be
stressed that scavenging may be part of both cases. So
you know, on one hand, you have like straight up
predation like well there's my competitor, I've got the drop
on them. I shall eat them, but also a situation
of well there is my competitor, they have died.
Speaker 3 (26:10):
What you're going to do, right, yeah, because often in
energy relationships like this, trying to prey on a healthy
adult of like a of a competitor within the food
chain is usually going to be kind of dangerous. So
I think we've read about integuild predation before, some of
(26:30):
it being not predation but scavenging, but other ones being
like adults of one species preying on the young of
the other.
Speaker 2 (26:38):
Yeah, because you know, otherwise going toe to toe with
someone or something in the ecosystem that is your equal, Like,
that's that's a gamble, and survival is on the line
regardless if you engage in that struggle, And you might
only engage in that struggle if survival is already on
the line. And yeah, in the impoverished food web of
(27:01):
the dark, you get what you get. You don't pitch
a fit. Each of the species here that they looked
at consumed a wide variety of prey and indulged in
integral predation as presumably necessary. So it would seem, based
on what I was reading here that Yeah, while you know,
integral predation of course, as you said, occurs in the
sunlit world as well, and in the oceans and so forth,
(27:25):
within the cave environment, it might be more pronounced again
due to the limited scope of the available biomass, available
nutrients and so forth.
Speaker 3 (27:35):
Right, Yeah, I mean, the fact that it's a place
where food is scarce creates weird biological incentives and emphasies.
Speaker 2 (27:42):
Yeah. So yeah, I thought this was very interesting. But
I want to get into this other area here for
the remainder of the episode here having to do with
outsiders in the cave, creatures who have come into the
cave to take advantage of what is there. Because once again,
and there's the there, the there's the idea that the
cave environment comes with pros and cons. One con as
(28:05):
we as we've discussed already, is that the food chain
here is just less robust, uh specialized, obligate. Cave organisms
generally have carved out a very narrow niche in which
to live. A big pro, however, is, as with the OLM,
you're often dealing with fewer predators and a more secluded life.
Speaker 3 (28:24):
Mm hmm.
Speaker 2 (28:25):
It's like the Phantom of the Opera. You know, you
have this vast catacomb empire over which to rule and
row your boat around, and you have great acoustics, you know,
for your singing, for your your your cool pipe organ.
But the real music scene is upstairs in the sunlit world,
and you are, you know, to a large extent cut
off from that.
Speaker 3 (28:44):
You really need to kidnap a singer from up there
to to make your make your songs work better down there. Yeah.
Speaker 2 (28:51):
Yeah, So there there is a potential advantage here for
creatures of both worlds and creatures of the surface that
have figured out how and when to venture into caves
to take advantage of the creatures that live there, at
least live there periodically. And you know, I don't think
(29:11):
we've run across anything that's going in to harvest the olms.
But as we've been discussing one of the most abundant
life forms you might pray or scavenge upon the in
caverns are creatures that spend part of their time there
as well. That being bats, they roost in great numbers.
They enjoy a great deal of security there. But a
(29:33):
specialist could get in there and reap the bounties.
Speaker 3 (29:37):
Oh, I don't know if I ever thought about that.
So what would do that?
Speaker 2 (29:41):
Well, a number of organisms. Actually, I was looking at
a paper from nineteen seventy two. This is by Winkler
and Atoms titled utilization of Southwestern Bat Caves by Terrestrial Carnivores,
and this is published in the Journal of the American
Middland Naturalist. And they put out that various predators venture
into caves to enjoy the occasional bat feast, either via
(30:02):
active hunting or by scavenging for fallen bats. And this
includes broadly like various reptiles, raptorial birds, and mammals. For instance,
they point out that at Bracken Cave, raccoons and some
skunks were observed to venture into the cave to prey
on fallen bats at the cave mouth. Because you know,
(30:25):
I think we discussed this at least in passing earlier.
You have large populations of bats residing in many of
these caves, and occasionally bats do fall be they you know,
young bats, older bats, in firm bats, et cetera. They're
just too many of them this for this not to happen.
(30:45):
It will occasionally rain a little bit of food in
the form of a bat, and an organism that is
operated into tunistic enough can get in there and collect
those and eat them, or you know, eat them before
they're able to crawl across the cave floor and then
back up the walls to enjoy their roost again.
Speaker 3 (31:04):
So the cave buffet underneath the bat roost is mostly guano,
but occasionally bat meat as well.
Speaker 2 (31:10):
That's right. So ringtail cats were observed at another cave,
but it seemed as if, especially at Bracken Cave, raccoons
were the most likely to take advantage of the bat
bounty during both the day and the night. And in
you know, this this makes sense concerning the raccoon, because,
as we've talked about in the show before, you know,
(31:32):
they're they're great opportunists. Uh, they are. They're nocturnal omnivores,
and they have exceedingly wise pause.
Speaker 3 (31:41):
Oh that's right. I'm just now recalling that we did
an episode a while back about their apparent their strange
apparent washing of food behavior and the question about like
whether that really is washing or some other type of
behavioral instinct. And oh, I can't remember off the top
of my head what episode that was in, but I
remember that that that one really got my mind going.
Speaker 2 (32:01):
Yeah, I remember talking about like, for instance, they are
they are they're great opportunistic organisms that can adapt to
various environments. So they've done quite well with urban environments.
Uh and uh and yeah. We also discussed the heartbreaking
video footage that you can look up online of a
raccoon attempting to to dunk it's uh it's a plunder
(32:24):
of cotton candy into the water, and then seemingly confused
as it draws the bounty back out of the water
and finds that it is no longer uh there for it.
It's again kind of heartbreaking to.
Speaker 3 (32:37):
Watch yeah, totally. I just looked it up. By the way,
it was in our series on animals, quote cooking things
on the cuisine and kitchen behaviors observed in animals, including
the apparent washing of food. But again, I think there
was a question of whether that's really what raccoons are
doing or not.
Speaker 2 (32:55):
Yeah, but they're they're they're they're little paws, they are
little hands. If you will are are are excellent. I've
seen it described that they can essentially see with their
hands in ways that we could maybe relate to on
some level, But as is often the case with the
sense worlds of animals, of non human animals, we generally
(33:15):
can't fully imagine what it's like. Like they can see
with their hands is the best way that we can
perhaps understand it.
Speaker 3 (33:23):
Yeah, yeah, that was one of the hypotheses. It was
like that the water somehow hypercharges the sensitivity of the
hands and sensing the food. Yeah.
Speaker 2 (33:32):
Yeah. Now this cave in question, Bracken Cave. This is
a Texas cave outside of San Antonio that is home
to the largest known bat colony in the world. Some
twenty million Mexican free tail bats roost here between March
and October. This also apparently makes it the largest known
concentration of mammals period, including humans. I'm assuming, and I
(33:56):
imagine this takes into account the size of the cave
and the estimation estimated concentration of bats as compared to
human cities. But even among human cities, there are only
something like six cities with populations of more than twenty million.
So we're talking a lot of bats. And I didn't run,
I didn't look up or do the math on this,
but you know, you think about twenty million bats, how
(34:17):
many bats are going to potentially fall? So that does
create a certain opportunity for animals that are willing to
get in there day or night and pick them off
before they can get back up to the top.
Speaker 3 (34:29):
Yeah, with twenty million bats, I mean, even if you
assume a low death rate, that's got to be thousands
falling into the floor all the time.
Speaker 2 (34:36):
Yeah. Now, reptiles also get on in the action as well,
as that paper indicated, And one of the more alarming examples,
I don't know, it could be alarming, depends on what
you think about snakes is the example of yellow red
rat snakes found in a cave in Mexico that is
sometimes referred to as the Cave of Hanging Snakes.
Speaker 3 (34:58):
Hanging snakes.
Speaker 2 (34:59):
Yes, so, the yellow red rat snake is endemic to
Mexico and Central America, so it's fairly widespread. It's non venomous.
It prays mostly on rodents and birds and lizards, but
also on the menu are bats. So the Mexican cave
in question is Cantemo Cave in the Mexican state of
(35:22):
kintani Roo, about one hundred and eighty miles from Cancun,
known locally just as the bat Cave. According to Jose
Maria Morells, writing for Atlas Obscura, the snakes here have
developed an amazing method of eating those bats that doesn't
involve picking them off on the cave floor. So what
(35:46):
they do, apparently, is they crawl up into the cracks
in the ceiling of the cave as well as high
up on the cave walls. And then when the bats,
you know, the bats are roosting in there, so they
leave and then they come back. They leave to feed,
and then they come back. And when they're doing this,
when they're going in or out of the cave, that
(36:07):
is when the snakes will either dangle down or otherwise
like lash out to catch a passing bat in its mouth.
Speaker 3 (36:15):
Wow.
Speaker 2 (36:17):
And I've included a couple of photos here for you
to look at, Joe, one of the snake grabbing having
grabbed a bat and it's like, you know, just swallowing it.
And then there's another one of the snake up in
the recesses. This is these are actually, these are excellent photos.
They're from a Newsweek article that put that that profiled
these snakes.
Speaker 3 (36:37):
That is crazy. Now, I had a question that I
think I may have partially answered, but I just looked
up more images of these snakes jumping out to snag bats,
and my question was, well, how do they have the
leverage to do that? Because I was imagining them just
sort of like crawling up a cave wall. But in
some of the pictures I'm looking at, they have found
(36:58):
like a they're in like a recess, like a cubby
hole in the wall, and so I think they're gripping
something back there with the back half of their body
where they while they lunge out with the front half
to to grab a bat.
Speaker 2 (37:09):
Now you mentioned looking up images of this, Yeah, there
there are a lot of images of these of these snakes.
There's some footage as well. This cave has become an
ecotourism destination, so a lot of people have gotten to
go there. It's been covered in a lot of by
a lot of news outlets, various documentaries, so you can
definitely see some images of these snakes either you know,
dangling from the ceiling or consuming the bats that they
(37:32):
have acquired.
Speaker 3 (37:34):
Wow, that's one of those behaviors where it's like, I
would love an evolutionary account of how that arises, if
that's known, or if there's something suspected, like like how
long have these snakes specialized in attacking bats this way?
And like what were they doing before that?
Speaker 2 (37:51):
Yeah? Yeah, I mean I guess it's kind of a
natural extrapolation of surface world environments, especially thinking our boreal environments, right. Yeah,
the cave is just like a novel form of that.
And with the bat population, you have just such a
concentration of potential prey. You're going to have organisms that
(38:12):
are drawn to it and ones that are able to
adapt their existing practices, their existing predation and scavenging practices
to it, or as with the raccoon, are just generally
great opportunists. You know they're going to be able to
help reap some of that bounty for themselves.
Speaker 3 (38:29):
Well, Rob, thank you for introducing me to these hanging snakes.
I didn't know they existed, and now I love them.
So I think we probably have to call it there
for part three of our series on cave biology, but
I think we're going to be back for one more.
Three was not enough. There will be one more episode.
Speaker 2 (38:45):
I think, so. I think a fourth episode will wrap
it up for this journey into the caves, but you know,
after that, we'll probably be back in the future at
some point or another. Caves and their ecosystems and human
traditions associated with them are just too fascinating, all right.
In the meantime, we're going to go ahead and remind
everybody that's stuff to blow your mind. Is primarily a
science and culture podcast that publishes new core episodes on
(39:07):
Tuesdays and Thursdays, Sandwiched in between there on Wednesdays, there's
a short form episode for you monster fact Artifact, or
Anamalia stipendium. On Mondays we do listener mail, and then
on Fridays we set aside most serious concerns to just
talk about a weird film on Weird House Cinema. Usually
those are self contained single episodes, but if you're just
(39:28):
tuning into our channel for the first time, this week,
we are covering David Lynch's nineteen eighty four adaptation of
Dune in two parts, because it is that weird, that
packed with talent, and also, you know, Dune is in
the air right now, the spice is in the air
and we have to acknowledge that.
Speaker 3 (39:46):
Cool wahad Huge thanks as always to our excellent audio
producer JJ Posway. If you would like to get in
touch with us with feedback on this episode or any other,
to suggest a topic for the future, or just to
say hello, you can email us at contact at stuff
to Blow your Mind dot com.
Speaker 1 (40:11):
Stuff to Blow Your Mind is production of iHeartRadio. For
more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts,
or wherever you're listening to your favorite shows.
Stuff To Blow Your Mind News
Hosts And Creators
Robert Lamb
Joe McCormick
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