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>> Welcome, everyone, to
Wednesday Nite at the Lab.
I'm Tom Zinnen.
I work here at the UW-Madison
Biotechnology Center.
I also work for UW Extension
Cooperative Extension, and on
behalf of those folks and
our other co-organizers,
Wisconsin Public Television,
the Wisconsin Alumni
Association, and the
UW-Madison Science Alliance,
thanks again for coming to
Wednesday Nite at the Lab.
We do this every Wednesday
night, 50 times a year.
Tonight it's my pleasure
to introduce to you
Claudio Gratton.
He's a professor in entomology,
and he's also with the
Wisconsin Energy Institute.
He was born in Italy, but at the
age of eight he and his family
moved to Illinois.
His dad was on the faculty as a
physicist at the University of
Illinois in Champaign-Urbana.
That's also where Claudio got
his undergraduate degree.
Then he went to UC-Berkeley to
get his PhD, did a postdoc at
the University of Maryland in
College Park, and then in 2003
came here as part of a cluster
hire of a series of folks
working on agroecology.
Claudio tells me he does about
80% of his time on agroecology,
and the other 20% of his time
is on Iceland.
So we get to hear about the
icing on the cupcake, the work
that he does in Iceland.
Tonight's all about Midge
Madness in Iceland, and yes the
NCAA did let us use that phrase.
I'm very happy.
That would be the National
Center for Agronomic Acronyms.
[LAUGHTER]
Please join me on
welcoming Claudio to
Wednesday Nite at the Lab.
[APPLAUSE]
>> Thank you, Tom, for the
invitation and thanks for the
opportunity to come here and
talk to you about the minority
of my research, but, in many
ways, it's actually some of the
research that I'm most
excited about.
I get to work in very exotic
places and on some very
unusually abundant insects.
Most people try to find places
to go where there aren't any
insects.
[LAUGHTER]
And I actually try to find those
places where there are lots of
them, and this is really one
of them.
So what I want to do today is
introduce you to the stars of a
show in northern Iceland which
are very small, these little
midges, and hopefully by the end
of today, I'll have convinced
you that not only are they
interesting here, but they're
actually very important and
interesting in other places
as well.
And I'll talk a lot about their
ecology and how they affect the
ecosystems in which they occur.
The work that I'm going to talk
about is really part of a large
collaborative effort.
It involves a series of
postdocs, students,
collaborators on the faculty
here at University of Wisconsin,
a collaborator at the
University of Iceland as well,
Augie Arnason who's the director
of the research station out of
which we work there, and of
course the funding that we have
for this has been absolutely
critical.
So when we think about animals
that move, we often think about
animals like this big salmon.
These are not insects.
Salmon, they live in the water
and they move between the ocean,
where they spend most of their
adult lives, and the streams,
where they go to spawn.
So they have these mass
migrations where they move from
one ecosystem, the oceanic
ecosystem, and they move into
these stream ecosystems inland.
In the process of doing so, they
end up as food for big
carnivores on land.
They move energy and material
that originates in the ocean,
and they move it inland.
So this is a big movement of
energy in our environment.
Well, small things also move
large distances.
You've probably heard of the
mass migrations that
monarchs do.
They live their juvenile lives
and a generation or two in the
Upper Midwest and Canada, and
then at some point they move
down to Mexico where they
overwinter in these large
aggregations, and then they
slowly migrate back up into the
northern part of North America.
Big locusts migrations, these
are made famous in Africa.
As the monsoons come, the
locusts pick up and they move
thousands of miles to places
where the vegetation is
greening up.
So insects also have these large
scale movements that, as they do
this, they bring with them
energy, carbon, nitrogen across
large parts of the landscape.
So these terrestrial examples
are somewhat similar to what I'm
going to talk about today, and
that is these little guys.
They're not so little on the
screen here, but they're midges.
And these midges are non-biting,
they live mostly in the water,
and they act to link the aquatic
ecosystems in which they live
and the land where they end up
going to.
That's really the story that I'm
going to unfold today.
Most of the times when we think
about lakes in the landscape, we
really think about places that
accumulate stuff.
Water gets pulled down by
gravity into depressions in our
landscape, and that's where you
get streams and rivers and lakes
as well.
In fact, even in this picture
here you can see it as this kind
of bowl-shaped depression where
the water accumulates.
Well, there's a lot of really
interesting things that happen
in the water, not the least of
which is that this is habitat
for insects.
And the insects that live there,
and this is food for all kinds
of aquatic predators such
as fish.
If you're a fly fisherman, you
depend on understanding these
relationships between the
insects that live in the water
and the fish themselves.
You take advantage of that when
you go fishing.
But these insects also emerge
out of the water, and they end
up as prey for spiders,
for birds, for bats, for lizards
and other things.
Most of this work that is
summarized here has really been
looking at insects that live in
streams.
In fact, most fly fisherman will
tell you these are good places
to go fishing.
The work that I'm going to talk
about, and I should also say
that most of the work that
people think about when they
talk about lakes and land really
is from that perspective of
things getting drawn into the
water.
So the lakes are kind of the
recipient of things.
They're not the source of
materials.
So what I'm really going to talk
about is kind of that reverse
side of the story today.
What happens when organisms
leave bodies of water and enter
into the terrestrial areas
around.
And what I'll argue is that
insects, aquatic insects in
particular, by virtue of having
one life stage in the water and
another life stage out of the
water, act as a link between
water and land.
And that link is unappreciated
but very important.
So I'll use a case study from
where we work in Iceland as an
example of this ecological link
between lakes and land.
What I'll first do today is give
you a little background as to
where we do our work.
It's a really interesting place
in northern Iceland, a lake
called Myvatn.
The midges that occur there,
midges are in a family of flies
called the chironomids.
And then I'll talk about how
these flies move around the
landscape and what effects they
have on land when they get
there.
And hopefully by the end, I'll
be able to try to wrap it up and
convince you that this doesn't
only happen in Iceland but it
actually happens everywhere,
everywhere that there's water,
and that these effects are
actually much more widespread
than we typically appreciate.
So a little bit about where
we work.
Here's Iceland.
A nice satellite image.
The star is on Reykjavik which
is where most of us would go and
visit if we have any sense.
Most of the population is in the
south.
In fact, you can see it's also a
little warmer.
There isn't as much snow
and ice.
This is probably an early
springtime picture.
And you can also see that this
image was taken when the
Eyjafjallajokull volcano was
erupting.
This would have been in 2010.
You can see the ash plum kind of
moving southwards.
This is disrupted all those
flights in northern Europe
around that time.
Our work actually occurs at the
northern end of Iceland, in the
northeast, and you should know
that, if you don't know already,
the Arctic circle just touches
kind of the top of that red box
right there.
So we're really pretty
far north.
The eruption that's currently
happening right now, if you've
been following the news, is
actually just south of that
red box.
This is the Bardarbunga volcano.
And this is an image that I got
from one of our colleagues
that's there just a couple of
days ago.
It's a dramatic landscape.
This is actually not too far
from one of the places that
we work.
The land is raw and new, and you
can almost think of it, if
you've been to Hawaii and kind
of seen that on the big island
of Hawaii as kind of those fresh
lava flows, well pick that up
and put it in Alaska, and that's
kind of what Iceland is like.
Cold but stark and absolutely
stunning.
This is the lake where we work.
Lake Myvatn in Iceland.
As I said, it's just almost
touching the Arctic circle.
You can see that this in an
active geologic area as well.
You can see a big volcanic
caldera just to the right.
The steam that you see in the
top there in the image is
actually some geothermal areas
that are actually harvested for
energy.
And these odd creations on the
water over here are called
pseudo craters.
They're actually not craters,
but it's the action of lava
moving over a body of water and
then the steam that's trapped
underneath forms these
pillar-like formations.
There's only a few places in the
world where these actually
occur.
It's a shallow lake about the
same size as Lake Mendota, but
it's only about nine feet deep
on average.
There's a couple of deep places
that get down to 12 feet.
So it's kind of a shallow
bathtub.
And in some parts of the lake,
the water that comes in is
actually warm.
It's at around 75 degrees.
And it comes in high in
phosphorus, high in nitrogen,
high in silica, and as a
consequence of this, the
shallowness, the nutrient
richness, this is a great place
for algae to really bloom.
So the productivity, what's
produced, the algal production
in this lake is much higher than
one would expect at these
latitudes.
It's also a place of great
biological diversity.
Because of this productivity,
birds from all over
North America and primarily from
northern Europe and actually
Africa as well go to spend the
summers.
Here you can see a German artist
from the 1820s who spent some
time there, made some beautiful
drawings here of the pseudo
craters and all the different
birds and the eggs.
The eggs are actually harvested
by the local communities there
for food.
And it didn't escape this artist
here, if you look on the right
side of that image there, he
actually drew in the midges.
Myvatn, in Icelandic, actually
means midge lake.
My means midge in Icelandic.
So this lake is not only famous
for this biodiversity but for
these little guys.
This is what happens when you go
out on the lake and you drop a
core, a tube, a clear tube, into
the sediment of the lake and you
pull it up.
And what you can see here is
that top sediment, that greenish
networky sort of looking thing,
is actually all of the tubes of
the larvae of the midges that
live inside of the lake.
The midges, the adults live out
of the lakes.
They lay their eggs on the
surface.
The eggs kind of drop down.
They hatch out, and the larvae
live moving around the surface,
feeding on algae, feeding on
dead things, detritus.
Some species, like these here,
actually build tubes, silken
tubes that then actually grow
algae on the outside of the
tubes.
And if you were to take this
tube here and actually dump it
out onto a tray, which is what
we do pretty regularly, and
count up all the things that are
there, this is what it would
look like.
There's two species that are the
most common.
There's the big ones up there
and these kind of smaller sized
ones and then a series of other
kind of rarer things.
Two species of midges form the
majority of the biomass and of
the diversity that's actually
found inside of these in the
bottom of the lake.
You can get numbers up to 60,000
of these individuals per meter
squared.
That doesn't mean much to me,
but hopefully you'll see what
that translates to.
So this is what the adults
actually look like.
This is what happens when the
midges emerge.
When their larval stage is done,
they come out to the surface as
a pupa, they hatch out of their
pupa, and then they fly out as
adults.
All of this brown scum on the
surface is the pupil skins that
have been left behind by the
midges, and the boat is kind of
cutting through this right now.
That scum washes up onto shore.
If you pick it up and look at it
closely, there's all kinds of
little creatures that are
actually feeding on this dead
and decomposing material that
used to be midges.
And this is what the adults look
like from a distance.
The adults, this smoke that's on
the land right here are
aggregations of the adults after
they've emerged out of the lake
that move over the land and are
looking to mate.
This was in 2010.
This is what it looks like on
the side of a hill, also in that
particular year.
It's absolutely astounding.
Hopefully this will start.
This is a video that I actually
took this year.
This is what it looks like on
the grasslands.
They're coating everything.
When you're actually in some of
these swarms, it sounds like a
lawnmower.
There's no good audio right
here.
You have to keep your mouth shut
when you're working.
[LAUGHTER]
They're non-biting midges so
they're not looking for you.
They're not trying to get into
your eyes or your ears.
They're just very abundant, and
so it's inevitable to actually
get them in your eyes and in
your mouth.
The other interesting thing
about these midges that I won't
talk about today is that they
have very interesting population
cycles.
The populations aren't that
high, like I showed, every year,
but they actually fluctuate over
five orders of magnitude here to
the point where in some years
they're virtually impossible
to find.
We will drop that core down and
we will find one larva the
entire summer.
And other times we will find
60,000 per meter squared.
Or, as you can see here, some
years are bigger than others.
The periodicity of those cycles
is a question, is open for
debate.
What causes those cycles.
They happen irregularly, about
five to seven years.
From long-term sediment cores
that colleagues of ours have
made in the lake, there's
evidence that these cycles go
back probably several hundred
years probably to the beginning
of the lake, which was about
2,000 years ago.
So the midges have always been
there.
They've probably always been
cycling.
What causes these five- to
seven-year cycles we don't
really understand.
What seems not to be one of the
drivers is predators in the
water.
So this probably is not one of
your classic predator/prey links
sorts of interactions.
>> Are the cycles similar to
the locust?
[INAUDIBLE]
>> So the question is, are the
cycles similar to the locust,
the plague locusts that you
find, the biblical locusts?
Not that I know of.
Those tend to be more driven by
climatic factors.
Whereas, these seem to be driven
by some other endogenous factors
that have to do with how they
eat the algae and how they
displace themselves out of house
and home by completely
saturating the sediment of
the lake.
And we have an ongoing project
that's trying to understand the
cyclic nature of these midges.
I'm not really going to talk
about that today, but you'll see
some remnants of this.
So this, because of this
interesting and unique geologic
area, is actually one of the
best studied lakes in the world,
similar to Lake Mendota here.
A lot is known about what is
happening in the lake, all the
species that are there, the
nutrient flows, the things that
eat the midges inside of the
lake, the ducks, the fish,
arctic char and the
sticklebacks.
When I started working there, I
asked the obvious question of
the researchers that had been
there.
And I said, well, great, there's
all these midges here, you guys
know a ton about what's
happening inside of the lake, so
what happens when they end up on
land?
And they looked at me and they
said, we don't know.
Nobody knows what happens when
they end up on land.
We've been focusing on the
water.
So I thought, wow, this is going
to be a really interesting place
to come and actually understand
how it is that, what happens
when you have these mass
emergences of insects and the
kinds of interactions that
happen that can occur between
the water and the land.
And if you walk around the
grasslands and the lands that
are just around the lake, this
is often what you see.
All kinds of things taking
advantage of these insects.
These kind of soft-bodied
unprotected little guys that
come onto land looking for
mates.
Spiders here catching them in
their webs.
Here's a picture that I took at
around 11:30 at night, actually.
This was around sunset.
You can see this one grassland
here with all of these silver
silken strands of spider silk on
the grass.
Densities of these spiders that
you would never be able to
explain based on just the
availability of food that comes
from the grass itself.
The only way that we can explain
these high densities is by
understanding the midges and how
they come onto land.
There are some plants there.
This little pinguicula it's
called, butterwort, that
actually catches the midges in
its bract right here.
And we've since found that
plants that catch more midges
actually flower sooner and have
bigger flowers than plants that
don't.
So they affect the plants.
They affect the predators.
So, as an ecologist, I was
interested in the interactions
between organisms on land.
This is kind of a cartoon
version of how we often simplify
our food webs on land.
We think of them as, well,
there's plants there and the
plants provide food for some
herbivores, little insects, in
my case it's little insects that
feed on the plants, and then
there's some predators that feed
on those herbivores.
That's kind of your classic
food chain.
Well, at Myvatn, things are
turned around a little bit
because not only do you have
this traditional food chain, but
you also have these midges that
are coming in.
And the midges act as food both
for the predators, I showed you
those pictures of the spiders
eating them, but they can also
affect the plants as well.
So what happens to these
interactions when the midges are
around?
Do the predators just ignore the
herbivores and start feeding on
the midges, and so the herbivore
populations can explode?
Or are the midges affecting the
plants in a way that the
herbivores can take advantage of
that?
So everything that we had
thought of in this very nice
kind of neat way needs to be
rethought.
When you add this extra
component, this link from the
water to the land now makes us
rethink our food webs on land.
And to give you a little more
concrete example, the predators
that I think about on land are
things like these little wolf
spiders up here, harvest men or
web spinners like the ones in
the top right.
The herbivores are often sap
feeding insects that feed on
grasses and caterpillars or
other things that feed on the
foliage.
And the reality is that most
midges, with the exception of
that pinguicula that actually
can take advantage of the midges
directly, most midges are
actually decomposed by a series
of small arthropod decomposers,
springtails, mites, things that
decompose, that break down the
dead midges and then liberate
their nutrients so that plants
can actually take advantage of
them.
And the plants in these areas
are what we refer to as
heathland vegetation.
These are short, shrubby
vegetation that often doesn't
get much above the middle of
your leg.
Willows, dwarf birches, lichens.
So it's not forests.
In fact, there's almost no
forest in Iceland at all.
So we learned a little bit about
the midges.
They move onto land.
There's lots of them.
How many of them actually, the
first question we were trying to
get at was, how many are there
really?
Those pictures look nice, but
does that actually translate to
anything of significance?
So my student Jamin, who
actually gave one of these
Wednesday Nite at the Lab talks
a few years ago, went out and
tried to quantify how much
actually comes out of the lake.
And what he did is he moved
around the lake and he set up
these aquatic emergence traps
that actually sit just below the
surface of the lake and
intercept those flies as they're
trying to emerge out of the
water.
And we catch them in the top, we
do this in different parts of
the lake, and then we multiply
by the area of the lake to
figure out how much production
actually occurs.
And then we also catch the
midges on land through these
what we call infall cups.
And they're basically just deli
cups with a little bit of
preservative in them.
We leave them out for a few days
or a week, and after a while
they fill up like this and we
use that to tell us where are
the midges going and how many of
them are there.
And so what Jamin found is that
in 2008, which was one of our
high midge years, coming out of
the lake, out of the surface of
the lake, were about 55 metric
tons of midges.
55 metric tons of midges.
Again, that number doesn't mean
a lot to me, so did a couple
calculations here that might
help you.
So 55 metric tons converts to
about 110,000 kilograms in wet
weight.
So that was dry weight of
midges.
And I'm hungry right now because
I haven't had dinner, so I was
thinking how many Big Macs
is that.
If the average Big Mac is about
a pound, it's actually a little
less than a pound,
2.16 kilograms, every year
coming out of the lake is about
half a million Big Macs.
That's four tractor trailer
fulls of Big Macs produced every
year that comes out of the lake
and then gets scattered around
in the landscapes.
Boy, if that doesn't have an
effect on the landscape, I don't
know what will.
We actually saw that the midges
distribute themselves away from
shore in kind of these classic
dispersal curves, but they
aggregate themselves near the
shore.
And that's kind of a mating
phenomenon.
They're not right on the shore.
They're a couple, maybe
10 meters inland.
They like to move in just a
little bit where they have their
mating swarms, and the males and
the females kind of do their
thing.
Somehow they find each other.
Most of them drop to the ground,
and that's where they die.
The females will go back, lay
their eggs, and then we don't
really know what happens to
them.
Do they come back and mate
again?
Do they just die on shore?
Do they get blown away by the
wind?
We really don't know what
happens.
So this is kind of the
dispersal.
If you take the dispersal away
from shore and you calculate
what happens if we take those
55 metric tons and disperse them
over land, you can come up with
estimates of how many midges
should be landing per meter
squared of land.
And that's actually what this
picture over here is showing.
That we can get as much as
approximately 100 kilograms
dry weight near shore
of midges.
100 kilograms per hectare
per year near shore.
Since each midge is about
10% nitrogen, which is actually
pretty good, plants are about
2% to 3% nitrogen, insects are
about 10% nitrogen, this
converts to about 10 kilograms
of nitrogen being deposited in
the areas on the grasslands per
hectare per year just by the
midges coming out of the water
and dying on land.
I should say that in these areas
in the high Arctic, the amount
of nitrogen that just rains down
through precipitation is about
two to three kilograms.
So this is well above the
background rates of what's
normally falling.
Farmers in this area probably
fertilize with about 50 to 75
kilograms of nitrogen that they
put on their fields.
So these numbers are not
trivial.
And, in fact, the farmers
themselves, when you ask them,
you say do you think there's any
value in all these midges coming
out of the lake and then dying
on land?
They say, oh, yeah, of course,
we actually think that they have
an effect on the grass.
We have a term for that.
We call it midge grass,
my grass.
And that's the fertilization
effect that happens after the
midges come out and the grasses
actually respond.
And I thought, really?
I wonder if we can actually
measure that.
So with my colleague
Phil Townsend here in Forest
and Wildlife Ecology who's a
specialist in remote sensing, I
said, Phil, the farmers there
are saying that they see a
response or they argue that
there's a response of the
grasses around the lake after
the midges come out.
I that true?
And after I gave this talk, a
similar talk, he went back and
we dredged up some images.
This is a -- false color
infrared where the redder the
image is, the more vegetation
there is.
And what you can see is that
right around Myvatn, right here,
is this hot red ring.
And, in fact, what's really
interesting is that in that top
right corner over there where
it's mostly gray, that's a lava
flow from about the 1750s.
And if you look very carefully
right along the edge of the
water where it's black, you'll
see this pink hue right there.
So even where there is no grass
that the farmers are growing,
you're seeing some kind of
response by the vegetation right
there.
So this gave us an indication
that, wow, there's probably
something going on.
And, in fact, the areas nearest
to the lake look like this on
the right.
They're mostly grasslands.
Phil then actually quantified
this relationship, and he found
that using an index of redness
in these images you can see that
that redness actually decreases
as you move away from shore.
Boy, does that look familiar.
And that actually when you
compare that to lakes that don't
have midges, there are some
lakes nearby that don't have
them, their relationship
is flat.
So at Myvatn, you have high
redness which then drops off,
and at these other lakes you
tend to have no relationship
at all.
So, again, this gave us an
indication that there's a signal
there that is coincident with
what the midges are showing that
is also seen from remotely sense
satellite imageries.
We call this the midges from
space effect.
When you actually go into these
grasslands and you look at the
relationship between how many
midges are ending up on land and
how much plant material there
is, you actually see this
positive relationship.
The more midges there are, the
more biomass there is.
And the more midges there are,
the less heathland there is and
the more grasses you actually
have.
Grasses are actually
out-competing the native
heathland where all these midges
are coming in.
Grass is actually really good at
capturing the nitrogen.
Whereas, the native heathland
plants are adapted for low
nitrogen conditions.
So when the midges come in, the
grasses can actually out-compete
them, and so you have this shift
of the plant community from one
that's typically a heathland to
one that actually looks like a
grassland.
So this was all nice and good.
We've got these correlations.
The midges come in.
They're really abundant.
We see these patterns from space
that are coincident with what we
would hypothesize would happen
if the midges are having some
kind of fertilization-like
effect.
We see these patterns in the
grassland communities as well.
We thought, is this a real
effect or is this just a
coincidence?
This is just a big correlation
that I'm showing you right now.
Is this actually because of the
midges, or could it just be that
the conditions next to the lake
are just conducive for grasses
and maybe they're warmer.
Who knows?
Maybe there's something else
that's actually going on.
So what we did is we said, all
right, why don't we actually
experimentally try to create a
midge effect.
So what we did is during one of
these big midge emergences we
all went out with our insect
nets.
You can see David, my postdoc,
there with his insect net.
And we swept them around until
we literally had bags and bags
full of midges.
This looked so ridiculous that
the Icelandic television came to
actually video us doing this.
We literally have pillowcases
full of midges which we then
painstakingly dried, put them
into little baggies, and then we
went to a lake nearby that does
not have any midges, it's not in
the influence of those midge
emergences, and has a heathland
community, which is the typical
kind of low productivity
community.
And we actually took the midges
and sprinkle them on by hand
into little plots.
You can see one of our
assistants there taking the
midges and pretending that they
were depositing themselves onto
the grassland.
And then we started monitoring
these plots over time.
And here's what the plots look
like one year after the first
sprinkling of the midges.
And I'm going to, one plot is on
the left here.
You can see kind of the white
square, and there's another one
on the right.
Which one do you think got the
midges?
Absolutely.
This is one of those great
experiments where you don't even
have to do the statistics if you
don't want to.
You can just say, geez, that one
got the midges and that one
didn't.
We replicated this.
Obviously, you can actually
quantify this.
There is more biomass there.
That was a very rapid response.
So it's not to say that there
was no grass on the left to
start with.
The grass was there, it just
wasn't thriving.
It wasn't doing very well.
As soon as it got a little bit
of that midge nitrogen, they
immediately exploded like this.
We repeated this experiment in
the greenhouse.
We had plants that either had
nothing done to them, we either
added inorganic fertilizer, this
is what the farmers actually add
to their areas, potassium
nitrate, or midges themselves.
And you can see the same effect
in more controlled conditions.
And, in fact, the midge effect
was much greater than that of
the inorganic fertilizer.
So the midges are coming in, and
they bring in a tremendous
amount of carbon.
Carbon you can think of as
energy, food, calories for
things that are eating them.
They also bring nitrogen.
And the amount that they bring
in is much greater than that
that's observed from just
natural processes, natural
atmospheric deposition.
The plants seem to be
responding.
We saw this both in this
correlative sense across the
landscape, as well as through
our more manipulative
experiment.
And our next question was, well,
what about the other critters
that are living there?
Those things like the spiders?
The other organisms that we
cared about?
In those plots where we added
the midges, now mind you, these
are dead midges.
So web-building spiders that are
looking to catch things in their
webs are not going to be all
that excited about a dead,
crusty little thing that we're
adding.
So when we do this, the response
that we're expecting to get is
not going to be for those things
that need live prey.
But if you look at the total
number of other arthropods that
exist in those little
fertilized, hand fertilized
plots, compared to the control,
that's what this effect size is,
it's everything compared to a
reference condition that didn't
get the midges, we see that
there's a significant increase
in the abundance of arthropods
that are there.
Most of these arthropods are
things like maggots and other
small decomposers, like mites
and springtails.
So things that are taking
advantage of that dead midge
biomass that we're adding on
there.
In a couple of years, two years
after we started these
additions, we also saw the
increase of some predators and
some parasites.
And those particular little
hymenopterans, those were little
wasps that are actually
parasites of those maggots of
the fly larvae.
So you add the midges, the
plants respond, the decomposers
start to decompose the midges,
and then eventually their
predators, the predators of the
decomposers, start to build up
in those plots as well.
So we're feeling pretty
satisfied at this point.
To the point where we thought,
hey, if we can do a midge
addition experiment, why don't
we do a midge subtraction
experiment?
Why don't we go to Myvatn where
we know that there's a ton of
midges, and why don't we make
big cages and try to keep the
midges from coming in, and let's
see what happens in the soil in
those communities where we can
exclude midges.
And here you can see kind of
this top down view of one array
of plots that we had.
Those big white things are
closed cages.
There were some open reference
plots that obviously you can't
see from here.
And then those tattered things
are actually partial cages that
we intentionally wanted to allow
access by the midges but then to
create kind of a cage effect.
It's more of an experimental
thing.
But, no, we weren't bad at
constructing cages.
That was actually intentional is
another way to say this.
So we want to exclude the midges
and see if we got the reverse
effect.
So this is actually what one of
the cages look like as those big
swarms of midges, like I showed
you in that video earlier, is
actually occurring.
And the cages were great at
keeping the midges out.
Almost nothing could get in.
And I should point out that the
cages actually are open at the
bottom.
They actually don't quite go
down to the bottom.
They're just kind of rested on
the grass.
And the intent was that if
there's anything that wants to
crawl in and out of those cages,
we wanted that to happen.
The only thing we wanted to
change was access by the midges
to those cages.
So what do we get?
Well, I'm going to show two
pieces of information to give
you a little bit of insight.
The midges is really
interesting.
Because they live in the water,
they have a slightly different
chemical signature than things
that live on land.
And we're able to actually
measure that.
That's what's shown here on the
Y axis.
So midges have this carbon
signature that sits at around
negative 12.
Things that are on land look
more like negative 27.
Don't worry why it's negative or
exactly what this chemical
signature actually is.
But what we found was when you
take the midges out, when you
exclude the midges and you look
at the organisms that are in
those cages, you find that every
time you remove the midges, the
consumers, those things that are
feeding on land, have a decrease
in that chemical signature,
suggesting that the midges
aren't there anymore, they've
got to eat something else.
And they start eating things
that are more terrestrial-like.
And we see big differences with
some of those predators, the
opiliones, the --, the
harvestmen, those are the daddy
longlegs, what we call daddy
longlegs, wolf spiders, those
--, show these big decreases but
so do the decomposers, the
mites, the collembola, and some
others.
So you take the midges out and
all of a sudden there's a
different food that they're
switching to.
And so our thought was, okay, if
they're feeding on food that
comes from land and is clearly
less abundant than all those
midges that were there, we
should see a difference in
numbers as well.
Oh, I wanted to show you this
first.
This is a clever little
experiment that Jamin did where
we actually found that the
spiders, the wolf spiders in
particular, are really keen
about the midges.
There's something about the
presence of a midge that is very
attractive to the spiders.
Here's the experiment that
he did.
He took a container, like these
over here, and he either put a
sitting duck prey, a little
leafhopper or a little fly
maggot, in there, and then he
saw how many survived by
themselves in the absence of
spiders.
And that's the big white bar
there.
A bunch of them survived.
As soon as you throw a spider in
there, the dark gray bar,
survivorship goes way down.
The spiders are eating the prey.
That's great.
As soon as you add as few as
five midges into the container,
all of a sudden the spiders
become distracted, and they're
no longer feeding on those other
sitting ducks that were left
before.
And it doesn't matter if you add
five midges or a hundred midges
to those tubes, the spiders all
of a sudden are mesmerized.
And they're no longer paying
attention, at least not as much,
to those other prey that
previously they were feeding on.
And, clearly, when there's a
hundred midges around, the
spiders are not eating every
single one.
So there's something about the
movement or the buzzing or what
it is.
We don't know exactly what it is
that is very captivating to the
spiders that distracts them from
actually feeding on the resident
prey.
So back to the other story.
That is, what happens to the
numbers?
Given that when we block the
midges, this distraction effect
shouldn't be happening.
We know the spiders shift to
feeding on things that are on
land.
What's going to happen?
And here's a bunch of data, and
all I want you to do is kind of
tell me if there's any pattern.
The blue is the control, that is
full access of the spiders, of
any of these consumers, to the
midges, and the red is where we
completely block them out.
All right, the bottom line is I
don't see any difference here.
For four years we did this
study.
We actually continued it one
more year.
And to me those lines look like
they track themselves almost
perfectly up and down.
Yeah, there's variations.
Some years are higher than
others.
Yeah, sometimes they go up and
they go down.
But for the most part, there
were no differences in numbers,
which really baffled us.
So the midges are so abundant,
they should provide this great
food resource.
We know they're feeding on them,
and yet, when you completely
block them out for four years,
we see no differences in the
abundance of any of these
organisms.
We're still scratching our head
about this a little bit.
But one of our interpretations
of this is that if midges come
on land long enough, centuries
perhaps, and the plants grow and
they die and they accumulate
dead material and the dead
material decomposes and then it
creates conditions to get more
plants, that there's an
accumulated layer of resources
there that even if you block out
the midges for four years is
still able to fuel these
communities here, even in the
absence of midges.
In a sense, the experiment that
I showed at the beginning where
we go to an area that's never
seen a midge and we add some
midges, we get this very rapid
response.
If we were to do that for a
hundred years and then we stop
adding midges, it may take a
very long time for that system
to kind of go back down to what
it was before.
To kind of re-equilibrate to
these no midge conditions.
Four years clearly wasn't enough
to actually get there.
And we don't know how long it's
going to take.
So in a sense, the plant
community changes, but they
change and they have this
storage capacity.
They kind of have this long-term
dynamic where as the midges come
in every year and then they have
these cycles, the plants
actually act in a slightly
different timescale.
And, in fact, maybe from the
plant perspective, they can't
even tell that the midges are
cycling because of that storage
capacity that they might
actually have.
This is a hypothesis that is
going to require, clearly,
long-term data to actually
get at.
All right, where does this leave
us?
Midges are bringing in lots of
carbon, the plants respond, and
so do the consumers on land, in
particular the decomposers, but
so do the spiders, at least on a
short-term basis.
They have this behavioral
distraction effect by
the spiders.
So hopefully at this point
you're saying, okay, Claudio,
this is pretty cool,
but this is Iceland.
This is just a freak of nature
lake that you're studying.
It's very peculiar.
How does this apply to
anywhere else?
Why should I care about this,
other than this is just kind of
an interesting story?
So is Myvatn special?
Is there anything that we can
learn from our studies at Myvatn
that we can apply anywhere else?
You guys live here in Wisconsin,
maybe some of you have been on
the Mississippi in July.
This is a Doppler radar image,
Doppler is a ground-based radar,
taken on a clear night, so
that's not clouds and rain
that's actually forming, during
a mayfly emergence on the
Mississippi.
This is large enough that it can
actually be detected from these
ground-based radar.
And I took this from a 2006
image.
You can actually go on the NOAA
website and every year they have
a new update, and you can see
this every year.
So this wasn't just a freak
year.
I saw the one from this year as
well.
Here's a picture from 1966 in
the La Crosse area where this
gentleman here is literally
picking up handfuls of mayflies.
Who knows where this is?
Excellent.
This is Devil's Lake.
Yeah.
This is a picture that I took in
2009.
One of my friends said, hey, you
got to get down here.
There's midges.
It looks like Iceland.
And I drove there, and, well,
it's like a mini version of
Iceland.
In fact, if you ask the park
rangers there about the midges,
they kind of roll their eyes and
they hand you a brochure.
[LAUGHTER]
Actually on the midges of
Devil's Lake.
So mass insect emergences are
not exclusive to Iceland.
In fact, they occur everywhere.
They occur from rivers.
They occur from lakes.
In fact, if you do the following
thought experiment, which is
what we did, within 20 meters of
any body of water, if you
calculate the amount of area in
Wisconsin that's within
20 meters of any body of water,
either a lake or a stream, you
find that about 9% of the land
area is within 20 meters.
And if you take that out to
200 meters, that a third of the
land in Wisconsin is adjacent to
some body of water within a
200-meter radius.
If those dynamics that I just
explained, that are argue are
occurring in Iceland, if those
same dynamics are occurring in
Wisconsin as well, both in
streams and in lakes, perhaps as
much as one-third of the land in
Wisconsin could be under some
sort of influence of these
aquatic insects.
And so we actually did a little
model that took those dispersal
curves, and we made some
guesses, educated guesses, about
how many insects should be
coming out of the water in these
bodies of water in Wisconsin.
And we said, okay, where in the
landscape should we be seeing
insects, and how abundant should
they be?
And here's just a close up of
one area over here.
You can see over on the right,
over there, you can see
Lake Winnebago.
Big lakes should produce more
insects just because of their
size that then splatter
themselves up on the edges.
So you can see that dark red
ring there, which is where we
would predict we would find more
insects, more midges, or
actually more aquatic insects in
general.
There's a northern lakes region
where the lakes are smaller but
there's lots of them, and their
sphere of influence from one
another actually overlaps.
So there's an area up there that
we would expect that insects
would actually have, in total,
a much bigger effect as well.
Mendota and the Yahara Lakes,
you can see it kind of in the
lower area here.
Anyone who's been on the terrace
in the summer probably has seen
small little swarms of these
midges.
And most of them are
chironomids, the same thing.
These numbers that we come up
here correspond to about the
same amount of insects that are
produced from the insects that
actually just develop on land.
Those insects that feed on
plants and kind of grow based on
terrestrial food, the number of
those is equivalent to the
number that is actually coming
from the water and joining them.
So the aquatic influence is,
again, not trivial.
And I want to leave you with
this last example.
It's not an example.
It's an analogy that I've tried
to think about.
So should we think about lakes
differently now that we
understand these particular
dynamics?
And I think about the landscapes
where we walk through and we
live day in and day out.
Here's out beloved Madison and
the University of Wisconsin
campus.
If you were to walk around this
area south of Camp Randall
Stadium, Regent, Monroe, just to
the west of it, and you were to
say, there's some interesting
aspects to this landscape here.
I see a high density of shops
and restaurants and bars.
Is there a way that I can
actually explain this?
Is this just random pattern in
the landscape, or are these
patterns non-random?
Is there something that is
explaining these patterns in the
landscape?
And I'm making an analogy here,
but we know of some things that
happen in the landscape.
Here's one thing.
[LAUGHTER]
This fills up a couple of
weekends per fall, or every
other weekend in the fall.
People come in and when the show
is over, people burst out and
spill over and outside into the
landscape ready to spend money,
to frequent establishments, to
buy T-shirts and so on.
So what we see in our landscape
around us is actually affected
by some of these features that
are in there.
Now, we know some of the
dynamics that actually play out
in our neighborhoods and how
people are coming together and
then disperse out from them.
And in their dispersing, they're
moving, they're creating an
economy.
They're moving money and
resources around.
Well, I guess I think of insects
in lakes the same way.
We're learning something about
their dynamics within the lakes,
and what we didn't appreciate
before is that those dynamics
actually spill out into the
landscape and affect the
economics, if you will, the
ecology of the surrounding area
through the movement of the
currency that matters there,
which is energy, prey items,
nitrogen, and so on.
So I guess this is kind of the
last take-home message, the few
take-home messages that I want
you to leave with.
That aquatic insects, because of
that duality of their life, the
larval stage in the water, the
adult stage out of the water,
have the ability to link aquatic
and terrestrial systems.
They move their bodies, and in
doing so, they're moving energy,
carbon that can provide food, as
well as nitrogen which is a
limiting resource for plants.
And it has consequences for
those things that eat them and
those things that can take
advantage of that.
And hopefully the lessons that
we're learning from this remote
part of Iceland has shown us
that this is probably an
underappreciated phenomenon.
That even though it's in grand
scale there, it's probably
happening everywhere.
Even if to a much lesser degree,
including here in Wisconsin.
If you want to learn more about
what we do, visit our website.
There's information both at the
website, and we have a research
blog that highlights actually
some of the daily goings-on of
our research.
Next year will be my 10th summer
there, actually.
So I'll have seen two complete
cycles.
And, of course, you can follow
us on Twitter as well.
And it's been a great group of
people to work with.
If you really want to see some
of the goofy things that we do,
you can also look for one of our
music videos that we've
produced.
[LAUGHTER]
That highlight the beauty of
Iceland as well as some of
the people.
Thank you very much.
[APPLAUSE]