The most dramatic moment of learning in my life
happened in less than a second.
I stuck my head in the water, and I thought,
"This is unbelievable."
50 years ago,
a group of scientists set off around the world to unlock the mysteries of nature.
I had never seen anything like this before.
Whether it was terrestrial or aquatic,
whether it was arctic or tropical,
it was all working in the same way.
We found the rules -- how systems work, how the world works.
This was a major deal.
Their collective knowledge proved
that some animals are more important than others.
If you lose the wrong ones, if you lose the keystones,
you're going to see very big changes.
These findings were revolutionary,
a new insight into nature.
Join these unsung heroes as they tell their unique story of hope...
...of how we can preserve life on our planet.
There's a sign when you get off the airplane there --
"Not the end of the world, but you can see it from here."
They ventured into the wild,
from the coasts of Alaska to South American jungles.
I was stunned.
I had never seen anything like this before.
In North American Rivers, And on African plains,
they followed their passion to explore.
I'd longed to be in such a place
ever since I was a small boy.
Their quest pursued over a lifetime
was to understand how nature is put together.
I'd try to go out looking to see how the world works.
I've always said that science is detective work.
There's a mystery to solve.
Science can tell us what's happening
when the naked eye can deceive us.
And now, after 50 years of research,
their discoveries fit together.
Whether it was terrestrial or aquatic,
whether it was arctic or tropical,
it was all working in the same way.
This was a major deal.
It is a blueprint to help heal a battered planet.
It was a flashbulb moment.
Nature could heal itself.
I've never in my life felt such an excitement.
We found the rules -- how systems work,
how the world works.
This is a story of hope
that will change the way you see nature.
It begins in the Pacific Northwest.
Bob Paine is a newly-minted biology professor
at the University of Washington.
It was exciting. I was totally naive.
Basically hadn't seen any of the Pacific coast ecosystems.
As a naturalist, he's trained to observe and record,
but Bob is thinking more radically.
He wants to see how things work by manipulating nature.
When Bob was in school, the general idea
was that all natural communities are arranged the same way.
The sun's energy drives the structure of life.
Plants grow using sunshine.
Grazers eat the plants, and they in turn are hunted by predators.
Everywhere on earth, nature is organized from the bottom up.
Yet Bob Paine is most fascinated by the predators at the top.
Could they play a more important role
than simply eating a little meat
at the summit of a food pyramid?
But how do you test that?
You can't just get rid of all the bears
or eagles from a forest to see what happens.
Bob Paine needs a natural community
he can easily manipulate.
At the tip of Washington's Olympic Peninsula,
he stumbles upon a small but magical world.
Few biologists had paid much attention
to the tide pools along this rocky shore.
But for Bob, they present the opportunity
he's been dreaming of.
There it was spread out in front of me.
It was Nirvana.
He realizes these tide pools are a complete ecosystem,
but in miniature.
This magnificent array of organisms.
There were carnivorous gastropods feeding on barnacles.
There were sea urchins feeding on algae.
There was a lot of pattern.
For Bob, the tide pool is a natural laboratory.
There are hunters and filter feeders,
scavengers, and plants giving food and shelter.
And among the mussels and barnacles,
anemones and snails, a large predator lurks.
Despite appearances, starfish are skilled hunters.
Each of their arms carry eye-like sensors.
Starfish use their tube feet to pursue prey.
They can pry open mussels, devouring them in their shells.
Here, Paine conducts one of the simplest experiments
in the history of biology.
He removes starfish from one tide pool,
while leaving them in another.
Month after month, Paine returns,
clearing out starfish.
And he sees the tide pool changing.
There are more mussels, but less of everything else.
Eight years later, the impact is dramatic.
The mussels are all that remain.
That indicates that the starfish
have been preventing the mussels from taking over.
The predator maintains the entire community
from the top down.
Without them, it all falls apart.
In other experiments,
Paine removes different species from the tide pools.
But when he does that, nothing changes.
The starfish alone hold everything together.
So Bob christens them a "keystone species."
I knew that I had discovered something important.
I'd changed the nature of the system.
I used the line in George Orwell's "Animal Farm."
"All animals are equal,
but some animals are more equal than others."
And that expresses the fact
that all species don't have the same impact
on the system they're in.
Bob's discovery of a keystone species
prompts more questions.
Do they only exist in tide pools?
What's the scale of their influence?
New revelations will soon link starfish
to sea otters
living thousands of miles farther north,
in the remote Aleutian Island chain off Alaska.
The connection will be made by a young man
who has yet to hear of Bob Paine's work
and isn't even sure he wants to be a marine biologist.
Everybody has to do something.
I was actually thinking about doing a lot of things
other than biology.
I was thinking first and foremost
about surviving, you know, making a living,
being able to make my way in the world.
One of my former professors at Washington State
was a consultant with the Atomic Energy Commission.
And they were looking for somebody to go out
to Amchitka Island and work on sea otters.
I had never worked in the ocean.
I was not a marine biologist.
I knew nothing about the ocean.
And he said, "You know, I think you'd be perfect for this."
Two weeks later, I was on my way to Amchitka Island.
There's a sign when you get off the airplane there --
"Not the end of the world, but you can see it from here."
I had this feeling of both excitement
for the beginnings of a new life
and also an incredible sense of trepidation
over whether I would succeed or not.
In the seas off Amchitka Island,
Estes gets to know the sea otters.
Highly social, they spend their entire lives in the icy water.
Without blubber for insulation,
they have evolved the densest fur of any mammal.
Sea otters are masters of their underwater realm,
the kelp forest.
It is spectacular.
It is absolutely one of the most amazing scenes
that I've ever seen.
Kelp to the coastal ecosystem
is like redwoods to a redwood forest
or oaks to an oak forest.
The kelp forest is an important foundation
for the coastal ecosystem.
Like any forest, kelp is a rich source of food,
home to dozens of species.
Estes is interested in how kelp can support
everything from spiky urchins...
to the large sea otters that eat them...
...how everything is organized from the bottom up.
But his world view changes the day he encounters Bob Paine,
who is visiting Alaska to meet with a student.
The instant I met him, I thought,
"There's no way I'm going to talk to this guy."
He just scared me to death.
He was very smart, very intimidating.
And he said, "You want to sit down
and talk a little bit about what you're doing?"
i told him that I was interested in following this notion
of how kelp forests could support so many otters."
He said, "It sounds pretty dull to me."
"Why don't you think about these animals as predators?"
It just immediately occurred to me
that this was a phenomenally interesting natural experiment.
And that was sort of the beginning
of the rest of my life.
Paine's question turns Estes' research on its head.
Instead of asking what the kelp forest does for the otters,
Jim now asks
what are the otters doing for the kelp forest?
When Bob planted the seed
of looking at the effect of otters,
it naturally occurred to me that the way to do that
would be to go to someplace where they didn't occur
and compare that with where they did.
If the otters are having some big effect, I ought to see it.
If I go to a place where they don't occur, I ought to see it.
Having nearly been wiped out by the fur trade,
sea otter populations are recovering
and spreading out across the Aleutian Island chain.
But the otters have not yet reached the shores
of the most remote islands.
One is called Shemya.
The most dramatic moment of learning in my life
happened in less than a second.
I stuck my head in the water at Shemya,
and I thought, "My God.
This is unbelievable."
I'd never seen an urchin barren before going to Shemya.
From having watched otters for extensive periods of time,
I knew they ate a lot of urchins,
but it never really occurred to me
until I actually saw a system where otters were gone
that the effect was massive.
Unchecked by the otters,
the sea urchins have gorged on the kelp.
That has started a devastating domino effect
right through the community.
The kelp forest and virtually everything that lived here
is gone.
Jim has discovered that sea otters, like starfish,
are keystone species.
I sat there all night long.
I didn't sleep at all that night.
All I did was write.
I think I had some sort of visceral sense
that this was a major deal.
I've never in my life felt such enthusiasm and excitement
as I felt at that moment.
Jim Estes takes Bob Paine's keystone discovery
to a new level.
Both large and small marine habitats
seem to be held together by single keystones,
whose removal is catastrophic.
The potential power of keystones
begins to attract the attention of other biologists,
who ask new questions about how keystones work.
Freshwater ecologist Mary Power
now wonders if the influence of keystones
goes beyond predators simply eating prey.
An underwater hunter would help Mary see something
neither Jim nor Bob had.
Ironic perhaps, because growing up,
Mary couldn't see well at all.
When I was a child, I was severely myopic
from who knows what age.
I didn't know that you could see leaves on a tree
from the ground.
But something happened before I got glasses,
and that was that I was let loose
with a mask and snorkel.
For the first time, I saw things clearly
because of the refraction of the water.
You can imagine how beautiful it would be
when you see detail that you'd never known you could see.
What were pondweeds above the water
were forests of stems under the water.
And in this little forest, there would be sun fish.
Then occasionally, a big, larger predator like a pickerel
or a perch or a bass goes by.
It was a flashbulb moment, as they say,
where I just had to be underwater
looking at life that way, for the rest of my life.
Following her passion, Mary Power focuses her studies
on fish in the rivers and streams of Oklahoma.
Her keen eye soon notices a striking difference
between some stretches of river and others.
Some pools are like mini green forests,
teeming with life.
Here, largemouth bass are the top predator.
But other pools are barren.
Bass are nowhere to be seen.
Here, small minnows eat everything
right down to the bare rock.
Power suspects bass might be a keystone
holding the community together in the lush, green pools.
To test her hunch, she designs her own version
of Bob Paine's starfish experiment.
We split the green pool into two halves.
We netted out the bass,
and then we added minnows just to one side.
And we sat back and waited.
In just five weeks, on the side without bass,
the minnows have reduced the green pool to rubble.
With the top predator gone,
the minnows overgraze the plants.
But there is something more in the green pools.
The bass are not just eating the minnows.
Mary realizes the predators instill a "fear factor."
About half the effect of bass
is due to terrifying the minnows
so they not only stop feeding, but they emigrate.
And that's a landscape of fear.
Bass are keystone species just in the sense
that Jim's sea otters or Bob's starfish are.
But there is still a major piece
of the puzzle missing.
No one has shown that keystones exist on land.
That search will turn up something unexpected
and sound an urgent alarm.
The scientist that will ring it spent a lifetime in the forests,
beginning when he was a boy.
I loved being in the forest.
Not see people, just be in the forest.
Some of my fondest memories of that period
were of catching fireflies in the evening.
Every summer, they would emerge about sundown
and then come up one by one.
There were birds that would sing on into the night and frogs,
and I've always loved listening to the evening and night sounds
in Virginia there.
John Terborgh will go on to become a forest ecologist,
working primarily in the tropical jungles
of South America.
It is from here that he will mull over
the concept of keystone species.
Mary Power's work in streams,
Paine's work in the intertidal,
and Jim's work in the ocean --
They did seem to work in a wide range of aquatic environments.
So at that time, I started daydreaming,
how could I expand on this?
Forests cover a third of our planet.
If John can show keystones
holding together communities here,
it will suggest that their power is global.
Yet to succeed,
John still has to overcome the same basic challenge
Bob Paine had faced 25 years before...
...how to remove the predators.
What I needed was to do an experiment,
but on land instead of in the water.
That meant finding fragments of forests without any predators
but with everything else still there.
I didn't know of any such place until I learned about Guri,
and that's where it all began.
Guri was an area of tropical jungle
half the size of Connecticut,
flooded by the construction of a new hydro-electric dam.
Now wooded hilltops are small islands.
With little food to eat,
predators like jaguars face starvation
and abandon the islands.
Everything that should've been there was there
except for the top predators.
It was the perfect system
so that you could see what the response
to removing predators would be.
The impact shocks Terborgh.
When I climbed up and walked into the forest,
it looked like a hurricane had been through there.
Wow.
With fewer and fewer predators,
plant eaters ravenously devour the trees.
Whether it's howler monkeys or iguanas makes no difference.
Even size doesn't matter.
On islands without predatory army ants,
hoards of leafcutters wreak havoc.
On the mainland, leafcutter ants are controlled
by a species of army ant.
Without them, the leafcutters are 100 times more abundant
than they would be on the mainland.
The foliage had been stripped off the trees so many times
by this multiplicity of leafcutter ants.
A tree can only withstand that so many times, and then it dies.
It's all predation-driven.
You remove predators, then it leads
to the deterioration of the whole system.
To Terborgh, it's a chilling realization,
because we've been systematically targeting
predators for centuries
all across the world.
Our planet has been rapidly changing.
We've transformed it.
As we take out the top predators in our path,
nature is being decapitated,
the ties that bind entire communities broken.
What humans have done is take nature apart
layer after later.
From loss of top predators,
there's almost always loss of diversity.
After we understood that,
we coined the word "downgrading" to describe it.
John Terborgh's trained eye
now sees downgrading all around us.
I can see it.
I'm not sure just anybody can see it.
Science can tell us what's happening
when the naked eye can deceive us.
Remember we found at Guri that with no predators,
the herbivores increased,
and the ants literally ate down the forest.
We're seeing the same thing here.
It's not ants, it's deer, but out of control,
they can lead to the same rather disastrous consequences.
The deer have reached plague abundance.
And it's the deer that create this effect
as if you had taken a hedge clipper
and gone along on the underside of the branches,
removing everything between the ground
and what we call a browse line.
The deer plague started as we removed wolves
to make room for people.
Now the forests Terborgh knew as a boy
are collapsing.
If this forest were whole and natural
and reproducing normally,
you wouldn't see me from the camera.
There would be things in between.
But you can look way out there, and there's no obstruction.
The visibility is 100 feet or 200 feet.
It should be maybe 10 feet or 15 feet.
That's the difference. There's nothing in the middle.
It's a disappearing forest.
These big, old trees, they're the last of their generation.
When those oak trees die off,
there wouldn't be a forest there anymore.
I remember a better world, and now I see things
going in a direction that disturbs me enormously.
Every day of the week, I can't stop thinking about it.
Downgrading is a disturbing reality,
but is it earth's destiny?
The fate of the natural world
is the last thing on the mind of a young biologist
when he first arrives
in what appears to be a pristine natural wilderness.
In 1965, the Serengeti was not well-known.
There were hardly any tourists.
People weren't aware of the remarkable nature
of that ecosystem as they are now.
There was everything around me --
all of these species all mixed up together.
It was just too good to be true.
I'd longed to be in such a place ever since I was a small boy.
Little doe Tony realize, at that time,
the Serengeti is the midst of a dramatic change.
Tony joins animal counts that reveal
wildebeest and buffalo numbers are rising rapidly.
When I first started, the wildebeest
were somewhere around 250,000 animals.
By the time I'd finished three years,
there were 400,000 of them,
and everybody thought,
well, they must have reached their limit.
And the next time we looked, it was 700,000.
Four years later, they had doubled again
to 1.4 million.
We had a world record.
For a large mammal, they just don't do that sort of thing.
Tony determines the growing numbers
are the result of a rebound.
It turns out the wildebeest had been decimated
by a virus spread from cattle.
But once the virus was eradicated in livestock,
the wildebeest started to boom.
But was this a blessing or curse?
Our next speaker is a Mr. Tony Sinclair from Tanzania.
When Tony goes public
with his record-breaking results,
he thinks this is a good news story.
To 1.4 million.
But park managers fear
these increases can't be sustained.
Too many wildebeest will overgraze.
There was a deathly hush.
I wasn't expecting that reaction at all.
Everybody thought we were being irresponsible.
We should have been culling these animals
because they'll overgraze the place, destroy the habitats,
and they were going to cause a collapse of the system.
I just want to point --
It's already been proven!
But Tony believes the cattle disease
had artificially kept the wildebeest numbers low.
What he's observing is a natural reset.
The way I looked on it was that animal populations
have been in existence for millions of years
without having to have humans control them.
We decided we were going to stick to our guns,
and we prevailed upon the park authorities
not to give in to culling,
but to wait and see what was going on.
If we were wrong,
we could be destroying one of the iconic places on earth.
For the next three years,
Tony keeps a close watch on the wildebeest,
looking for signs they're overgrazing the grasslands.
But after two more counts,
numbers remain steady at 1.4 million.
At that point, we knew that the system
had leveled out of its own accord,
and there was no damage to the environment.
The wildebeest find their natural balance.
But what happens next amazes even Tony.
He and his colleagues witness an incredible transformation.
To our surprise, we found that all of a sudden,
things started to reconnect with each other.
Because the wildebeest were eating up the grass,
there was less fuel, and, therefore, less burning.
That allows young trees to grow.
Wildebeest, of course, do not eat trees,
and that allowed the tree populations to increase.
Tree populations that probably hadn't occurred since the 1800s.
Those trees provided more food for elephants,
for giraffes, and for many, many bird species.
And then there are many more predators
because there's more food for those, too.
The wildebeest in their huge numbers
were determining everything else inside the park.
I realized that wildebeest was a keystone.
We had always assumed that keystones had to be a predator,
but we realized that a keystone could actually be herbivores.
And if removing keystones causes collapse,
returning them leads to rebirth.
We were seeing a recovery,
an upgrading of the whole ecosystem for the first time.
Tony's work is marvelous.
I was delighted because here is recovery,
here is upgrading.
But it's a long, long process.
We're almost 60 years down
from Bob Paine's work with the starfish.
I think we're finally arriving at a much better place,
but it has taken that long.
They started out strangers,
each a witness to the power of keystones.
By 2008, the small bands of scientists has grown its ranks.
What was once maverick thinking is becoming mainstream science
with the discovery of more keystones from around the world.
It was only by listening to each other
that we realized we were talking about the same thing.
Whether it was terrestrial or aquatic,
whether it was arctic or tropical,
it was all working in the same way.
There wasn't anyone that argued,
"I don't see this in nature," not a single one of them.
Morphological...
Bob Paine was the first one to show it.
Throw away the starfish, and the biodiversity collapses.
The starfish is critical.
With new knowledge comes opportunity
and a plan for action.
And so our challenge will be to upgrade systems.
What we need to do is put the starfish equivalent back in.
It's critical that we replace species
that are central in holding ecosystems together.
Nature could heal itself if a keystone is released.
You can get enormous bang for the buck.
I can see now how to translate this everywhere,
on just about every ecosystem in the world.
In Yellowstone National Park,
the starfish equivalent is the wolf.
This keystone has been reintroduced
after an absence of 70 years.
Wolves were reintroduced
and began to feed on the elk.
Then lo and behold,
the vegetation began to respond
and change in very, very dramatic ways.
The willows and cottonwoods
began to sprout along stream-sides.
Birds came back that had disappeared long ago.
Beavers re-colonized.
Yellowstone's trees thrive because of wolves,
just like Serengeti's trees thrive because of wildebeest.
And even where predators are still missing,
like the Scottish Highlands,
simply fencing off grazing sheep has a dramatic impact.
Upgrading works on land and in water.
Add some bass,
and then add maybe a big pickerel or walleye,
and suddenly you might have a five- or six-level food chain.
The result?
In choked and barren lakes,
the waters clear and life returns.
Suddenly, you have an aquatic system
that produces both clean water and a lot of food for us
and a lot of recreation for us.
So far so good.
But can anything be done when a community
is not just downgraded, but almost totally destroyed?
This is Gorongosa National Park.
Like the Serengeti,
it's home to an incredibly rich mixture of animals.
Until 1977.
For 15 years, civil war ravaged Mozambique
and destroyed Gorongosa.
95% of all the large mammals were wiped out,
whether predator or prey.
Surely such devastation was beyond repair.
Or is it?
Paola Bouley, a former student of Jim Estes,
thinks there is still a reason for hope.
By the time I started my career in ecology
at UC Santa Cruz,
Jim Estes was teaching in our department
and that very year was just completing his pioneering work
on sea otters.
20-plus years later, I'm here in Gorongosa National Park,
trying to understand how we can restore balance
to this ecosystem.
Once the war was over,
security was re-established.
Year by year, the plant eaters began to return,
growing from small surviving populations.
Within little more than a decade,
there were more than 100,000 large mammals in Gorongosa.
It's a sign of the resilience of these species
and the fact that this ecosystem,
the habitats were still really intact.
There was space for growth here.
Problem was, virtually all the lions, leopards,
and hyenas -- the big predators --
were missing.
There were not enough to keep the large plant eaters in check.
Paola and her team were going to have to bring them back,
reestablish their roles,
and resurrect the "landscape of fear."
They began by protecting the few remaining lions,
which start to recover.
But lions don't hunt all grazers.
The park now needs more predators of different stripes
and with different tastes.
That's why in 2018, after months of complex planning,
they attempt to reintroduce wild dogs.
But getting them to Gorongosa is not simple.
For everyone's safety, including their own,
these feisty meat eaters have to be sedated.
The plane lands, and, of course,
I feel a huge sense of relief.
Yeah.
And it's the culmination of months of intense work
by teams across international borders,
so it's not a trivial operation.
It's hard to believe they're really here.
We transported them now to their new enclosure,
where they'll spend the next couple of months
just situating, getting used to each other,
getting used to their new home.
After bonding in a protected enclosure,
the dogs are released into the park.
It doesn't take long for them to make an impact.
It's like a wave of teeth...
...that just flush out animals, on termite mounds,
through grasslands, through forests,
and they chase until they tire down their prey and strike.
They're already fulfilling a unique niche
in the ecology of predators here in this park.
So, instead of taking warthog and waterbuck,
they're taking impala and bushbuck
and these smaller species
that have been pretty safe from predation from lions.
Introducing wild dogs is a big undertaking,
but it's paying off.
The dogs force the plant eaters to stay vigilant
and keep moving.
They're re-establishing the landscape of fear.
Over time, and with the return of more predators,
this should reduce overgrazing,
encourage trees and bird life,
and bring Gorongosa back from the brink of oblivion.
What we're demonstrating is these ecosystems are resilient.
If you give nature a chance, it comes back.
And I think that gives you hope.
Restoring our damaged earth is possible.
A small band of scientists has shown us how.
They've given us a new way to think about nature
and our place within it.
These keystones are really important
to the distribution and abundance of species.
But all of that is under the control of humanity.
Humans are hyper keystones in the sense
that they are all controlling.
Humanity ultimately is the driver of everything.
The behavioral change in humans
that I think is most important
is changing intolerance to tolerance.
There's a lot of progress that I've seen in the last 20 years,
and so I'm really pretty hopeful
that we will sort of have an interconnected landscape
that works for both people and wildlife.
Humans care. They don't want a destroyed earth.
But I don't think you get depressed
if you're fighting with some hope in your heart.
An upgraded planet is within reach.
A path forward is clear.
There are rules.
We can harness them...
...to heal our damaged earth.
The challenges ahead are formidable and complex,
but we are not alone.
We now recognize a powerful ally in nature itself.