SPEAKER: From zebra stripes, to cracked mud, to honeycombs,
patterns abound in nature.
Are these patterns just pleasing to the eye
or do they reveal something about biological processes?
For ecologists, understanding the mechanisms
underlying vegetation patterns can provide insights
into ecosystem dynamics.
Corina Tarnita never imagined biology would be her destiny.
As a three time Romanian mathematical Olympiad champion,
she excelled in geometry.
CORINA TARNITA: I was a pure mathematician to begin with,
so there was a lot of just sitting in my office
and thinking about very esoteric problems.
And then I think at around 25 I started
feeling that math is getting a little bit claustrophobic
and I'm learning more and more about less and less.
So I started to work on a mathematical biology
kind of question.
Africa, I think, is just fascinating.
Because a lot of what I do has to do with geometric patterns.
That in places where we have so many cities
and so much agriculture, you can't see natural pattern
anymore.
Whereas here you see it everywhere.
SPEAKER: Corina has come to Gorongosa National
Park, Mozambique, in search of new patterns.
CORINA TARNITA: Yeah, we're getting
close to those 100 meters.
SPEAKER: One of the main features
of the savanna landscape here are termite mounds.
Carina and her collaborator, Rob Pringle,
have shown that termite mounds are biological hot spots.
Termites create rich, moist soils
that enhance plant growth.
When seen from above, termite mounds
are islands of green on a drier and often more sparse
background.
ROB PRINGLE: If you look at this perfectly polka dot landscape.
CORINA TARNITA: Wow, look at this. look at all the mounds.
SPEAKER: Corina and Rob noticed that the spacing
of termite mounds looks very regular, but how regular is it?
Corina turns to a mathematical tool called the Voronoi diagram
and applies it to satellite images of termite mound
landscapes.
She uses the center of each mound
to generate a field of points that in turn partition
the landscape into regions.
Corina can now ask how many neighbors each mound has.
CORINA TARNITA: And so sometimes it will have five.
Sometimes it will have seven.
When you then average over all these counts
you'll find that the average number of neighbors is 5.99.
So it's basically six neighbors.
There was a Eureka moment when I realized,
they're actually hexagons.
They're packing the space in the optimal possible way.
SPEAKER: What sort of natural processes
could account for this regularity?
To find out, we have to know more about termite behavior.
CORINA TARNITA: Termites live in these mounds.
They are the centers of the territories.
I'm going to draw them as these green discs.
But in fact, they don't eat there.
SPEAKER: Termites forage for plant material
outside their mound.
Eventually, they bump into their neighbors.
Termites are extremely territorial
and this meeting zone becomes a battleground.
CORINA TARNITA: So what you find is
that they put a boundary exactly at the middle of the distance
between the two mounds.
SPEAKER: So a major driver in this system
is termite competitive behavior.
CORINA TARNITA: If the colonies are very different in size,
then the bigger is always going to win
and the other one is going to be killed.
So that explains why they should be roughly of the same size.
And all the same distance from each other.
Wow.
So this is 30 meters.
This is the neighbor.
Perfect.
SPEAKER: So termite competitive behavior
creates the hexagonal pattern that
allows the termites to optimize space and resources.
But are the termites in Gorongosa National Park
unusual?
How common is this packing pattern
of termite mounds across the thousands of acres of savanna?
CORINA TARNITA: Then it was just going to every single satellite
image that had termite mounds.
And every one that I took had exactly
the same hexagonal pattern.
That's what you hope to see.
That's something that's repeatable in every environment
where you have termite mounds.
SPEAKER: Competition between termite colonies
is not the only force producing patterns.
Corina's model predicted that in the areas
between termite mounds she should find vegetation patterns
at a smaller scale.
To find them, she needs to look from a lower elevation.
A drone is the perfect tool.
CORINA TARNITA: Oh, this is beautiful.
This is really beautiful.
So now we can actually see these patches
of darker and drier vegetation intertwined with the lighter
patches of soil.
SPEAKER: The maze-like pattern may not
be as obvious and regular as the mounds,
but it becomes clear when analyzed mathematically.
Together, these two patterns on different scales
combine to reveal a fundamental dynamic of the savanna
ecosystem.
CORINA TARNITA: Immediately after the dry season,
everything dies out, except for the mound.
And as you get precipitation, you
start to see that everything re-vegetates again.
As long as you have termite mounds there,
your system is much more resilient.
So things like you have an increased
frequency of droughts.
You may end up losing the vegetation
in between the termite mounds, but you're still
going to be left with the termite mounds.
If the precipitation comes back, they're
going to be able to reseed the whole system.
So they act as this double role of both delaying
the collapse of the system to desert and at the same time
helping with the rebound.
SPEAKER: So termite mounds are not only
major engineers of the savanna, they also
contribute to the stability and resilience of the ecosystem.
And the hexagonal pattern optimizes
the number and distribution of mounds across the landscape.
With climate change models predicting more water stress
in some savannas, understanding these vegetation patterns
on and between mounds will become a very powerful tool
for monitoring such ecosystems.
CORINA TARNITA: They're hugely important for conservation.
And they should be one of the primary things
that we think of conserving when we think about climate change.
Because they're going to help us keep
the system alive for a lot longer than we could otherwise.
SPEAKER: Understanding patterns in nature leads
to the discovery of new processes.
Mathematics is the language of nature.
And scientists like Corina are refining our dictionary
of that language every day.