Ten million species live on planet Earth.
Each one is remarkable.
But none can survive on its own.
All life depends upon connections.
Unexpected, invariably complex,
beautiful relationships between millions of plants and animals.
Starting in our jungles.
Wow!
It's a different world.
Why do jungles have more animals and plants than anywhere else?
And why can't this mighty brazil nut tree survive without an orchid
and this nimble little rodent?
Connections like these form the planet's great ecosystems.
They're vital for all life.
I want to show you our world as you've never seen it before.
DISTANT BIRD AND ANIMAL CALLS
Central America.
The narrow isthmus of land joining two vast continents.
This is Pipeline Road in Panama.
Named because it runs alongside an old pipeline that was put in
during the Second World War to get oil from the Pacific
through to the Atlantic Ocean.
And it cuts through some of the most pristine rainforest in this part
of Central America, and I have to tell you that amongst birdwatchers,
this is a hallowed place.
It's world famous.
FAINT BIRDSONG AND GENTLE HUM OF CRICKETS
Semiplumbeous hawk.
Green honeycreeper.
Blue-crowned motmot.
Black-tailed trogon.
I've been out here since first thing this morning,
that's about five hours,
and during the course of that time,
I've seen or heard 75 different species of bird.
Some of them are quite tricky to identify -
I've just got glimpses through the trees.
If I was to stay out here all day
and work really hard,
I might see as many as 200 different species.
During Christmas of 1989, a party from the Audubon Society came here
and recorded no fewer than 357 different types of birds.
It was a new world record, set in this area of rainforest in Panama.
To put that in context,
the most anyone has ever seen in Britain in a single day is just 143.
And it's not just birds.
In this tiny reserve, there are twice as many mammal species
as there are in the whole of the UK,
3 times more butterflies and 13 times as many frogs.
Perhaps this astonishing diversity is shown best
by the richness of these superb birds.
LOUD VIBRATING
Hummingbirds are nectar feeders
so they find these dishes of sugar solution irresistible.
But it's not just the individuals that are so dazzling,
it's the sheer variety.
Blue-chested hummingbird.
Long-billed hermit.
Violet sabrewing.
Black-throated mango.
And white-necked jacobin.
There are 59 different species of hummingbird in Panama's jungles.
The almost bewildering variety of life that you find in rainforests
is exhibited by almost every animal and plant group that lives there,
and it's the same in rainforests all over the planet.
It's the remarkable thing that sets them apart
from the rest of our terrestrial ecosystem,
and it's a profound example of what we call biodiversity.
The number of different living things in a given area at a given time.
The big question is why?
And it's a question that's been vexing scientists for decades.
Why are there so many different living things in the rainforest?
In Asia, rainforests cover hundreds of islands -
some small, some vast.
New Guinea,
Java, Sumatra.
Amongst them, some of the remotest places on the planet.
Across the Indian Ocean, Africa and the rainforests of the Congo Basin.
Further west still and we reach the Americas,
home to the Amazon rainforest,
the largest unbroken expanse of trees in the tropics.
Together, these jungles form an emerald band that circles our globe.
CLAP OF THUNDER
Here on the equator, there are virtually no seasons.
It's hot and wet all year round.
Humidity barely drops below 90%...
..and the sunlight is more intense than anywhere else on the planet,
day in and day out.
All of this rain and all of this sun
results in a phenomenon on a scale unseen anywhere else.
It's happening here, in these leaves, in all of these billions of leaves.
And even if you're a really hard-nosed biologist,
really pragmatic about life,
it's nothing short of miraculous.
It's the chemical process of photosynthesis.
What plants are doing is combining two very abundant ingredients -
carbon dioxide in the air, and water.
Two ingredients that are almost impossible to combine.
If we take carbon dioxide and water and mix them together,
even under great pressure, all we get is fizzy water.
On the other hand, when plants mix carbon dioxide and water,
they get something else.
They get food.
They get sugar.
More of these sugars are produced in a given area of rainforest
than in any other habitat because of the sheer quantities
of water and solar energy.
In fact, the energy captured by rainforests in one year alone
could power the UK for over a million years.
All of that energy
is turned into food,
quite literally out of thin air.
It's a bit like the botanical equivalent
of turning water into wine.
Photosynthesis might explain why there's so much life here.
But it doesn't explain why there are so many different types of life.
There's one very special animal that I'd like you to meet.
She's a leafcutter ant, and she's an ant with a challenge.
You see, her problem is that she can't digest leaves on her own.
She needs to take them back to her nest.
But what possible effect could a tiny pest like her
have on this immense forest?
There are plenty of plant pests in temperate forests,
but there's one crucial difference.
Temperate forests have winters
and each winter, the cold kills off creatures like the ants
and they have to rebuild their colonies
and start from scratch each spring.
But here in the rainforest, there is no winter
and as a consequence, the plants here are under almost relentless attack.
Our ant is just one worker among thousands in a single colony.
Each ant deposits her leaf fragment deep within the nest.
There it will be composted and turned into a fungal food
for the whole colony.
Added together, the impact of all of these thousands of ants is enormous.
It's relatively easy to work out
just how much these ants are harvesting.
We know there's around a hundred thousand in every nest,
and scientists counted
the number of journeys they made every day carrying pieces of leaf.
374,200.
They also measured the leaf area -
the total being carried each day by the ants - 11 square metres.
Multiply that up and during the course of a year,
it adds up to 3,855 square metres
and that is 20% of the leaf cover
that's produced here in the area of the forest
where these little guys are foraging.
That's one fifth of all of the leaves here
destroyed by nothing more than ants.
And that's just the ants.
Grasshoppers, caterpillars, slugs and snails...
everything seems to be eating its greens here.
Wherever you look in the forest, it's almost impossible to find a leaf
that hasn't been attacked by pests.
The simple fact that there's no winter
to kill off these pests is a huge problem for plants.
So to stand any chance of survival,
every single plant in the rainforest is armed.
And many are filled with toxic chemicals which render them inedible.
All of this has had a profound effect
on the evolution of the animals that live here.
Take a closer look at these creatures. What do you notice?
Many of them are plain weird.
They're unlike anything else.
And one of the strangest of all is found here in Latin America.
Here it is, and what an amazing animal.
Really charming as well.
But if we take a closer look at it,
you can see exactly what I mean by weird.
This is a female three-toed sloth.
And she's embarking on a 20-metre vertical climb to find food.
She is charming, but she's also quite unlike any other animal.
So why is she so weird?
Well, it's a direct result of a very peculiar diet.
You see, she is a very fussy eater.
Feeding on only one or two trees, the leaves of which are tough
and full of toxins.
But her gut has evolved to host bacteria
which are specially equipped to break down
these otherwise inedible leaves.
It's a slow process.
Digesting this salad can take weeks.
She gets so little energy from this diet
that she's forced to keep her movement to a minimum.
She's almost become part of the forest furniture.
So much so that other creatures have started to move in.
She's the ideal home for a colony of sloth moths.
The way she looks, the way she eats and the way she moves
are all a result of having to overcome
heavily defended leaves,
and THAT is why sloths are so weird -
they're specialists.
In order to survive in a rainforest, you need to be a specialist.
There are no jack of all trades here.
The battle between plants and animals goes on every day
and it's this battle that creates the jungle's biodiversity.
Let me show you what I mean, with one of the most toxic plants of all.
This a passion flower vine
and its leaves are laced with a pretty toxic defence.
Cyanogenic glycoside molecules,
and when they break down, they form cyanide.
As you might imagine, it works wonders
because cyanide is every bit as dangerous to insects
as it is to us humans.
Well, that is to the majority of insects, but not all of them.
These are caterpillars from a species of butterfly called Heliconius doris.
They have evolved a unique internal body chemistry,
to do what few other creatures can -
counteract the plant's deadly cyanide.
They even incorporate the poison into their own bodies.
And after metamorphosing into the adult butterfly,
their bright colours advertise their toxicity.
Very clever.
As one of the few animals that can eat these leaves,
they have this food source pretty much all to themselves.
But the downside is, they can't eat anything else.
They are wedded to this vine.
The adult butterflies will not lay their eggs on anything else.
But of course, plants evolve too.
This is a different species of passion flower vine.
It grows in exactly the same patch of rainforest as the first.
And were it to arm itself
with exactly the same cocktail of cyanide as that first plant
then clearly it wouldn't be able to protect itself
from these Heliconius doris caterpillars, so it doesn't do that.
It's changed very subtly the type of compounds that it's got in the leaves
that produce the cyanide.
And as a consequence of that, it's totally toxic
to this species of caterpillar.
A victory for the vine, perhaps?
Except THIS is a never-ending battle.
Another species of butterfly has evolved.
One that can cope with the different toxins.
Introducing Heliconius cydno.
Its wing patterning is a little different to that of doris.
But the most important changes are internal.
Because each of these butterfly species
has evolved to be able to eat a different type of vine.
The battle between plant defence and caterpillar attack never stops.
The result?
A proliferation of species of both vine and butterfly.
In fact, each species of plant and tree in the rainforest
has ended up with its own specialised pests.
It's become an evolutionary arms race.
Just as pest pressure is driving the diversity of trees,
the diversity of trees is driving the diversity of tree pests.
And it's not just the pests, it's their predators too.
Animals like this praying mantis are continually evolving
to try and outwit those pests,
which, in turn, are continually evolving
to try and outwit the mantis.
If conditions in the forest here remain stable,
and new species have time to evolve, one thing is for certain.
This rainforest will become a whirlpool of biodiversity.
Now, it's easy for us to think of biodiversity as a wonderful thing.
But the pressures that create this biodiversity
make the rainforest a very dangerous place.
Especially when it comes to the survival
of the forest's youngest inhabitants.
Let's think about it from the plant's point of view.
I've collected about 15 different types of tree seed here,
all of which have come from this small patch of forest behind me.
Now, imagine that each of these seeds represents a tree.
And imagine that the forest was made up of a single species.
Like this one, that the locals call prischaco.
What you'd have is a monoculture.
But in the pest-infested rainforest, this doesn't happen.
And here's why.
You see, imagine you're a seedling trying to germinate and grow here.
We know that each of these tree species
has a highly specialised set of herbivores which attack it.
So this one will be accessible to
all of the herbivores living on these trees.
Not a good situation at all.
But what if you were a different species of tree germinating here?
Then you wouldn't be susceptible to this particular set of herbivores,
and that would confer a real advantage to you.
Then there's a far greater chance
that it would prosper through to maturity,
that it would survive. And in fact...
..if another tree species were to grow here,
it too would enjoy the same advantages.
Reduced susceptibility to this type of herbivore attack.
The strategy spreads like wildfire through the forest.
What we end up seeing...
..is a complete mosaic of species.
A seedling is far more likely to survive
if it germinates in isolation,
far away from the parent tree, surrounded by different tree species.
So how do plants get their precious seeds away to safety,
away from their set of voracious pests?
To find the answer, I'm going to the jungles of Borneo.
Home to some of the largest animals in any rainforest.
In the Kinabatangan river, a group of pygmy elephants.
Among the herd is a baby, born only a few weeks ago.
Nearby, in the Sepilok sanctuary,
this young orang-utan is just days old.
They don't know it, but these youngsters are incredibly important.
Because not only are both species rare,
but both will play a crucial role in this ecosystem.
Orang-utans.
Absolutely extraordinary animals.
So easy to see why we generate so much affection for them.
And when you look into their eyes,
it's like a reflection in a not-so-distant mirror.
But there is another reason
why we should value both orang-utans and elephants.
If you're a tree, seed dispersal
and germination is a pretty risky business.
After all, you're covered with pests,
all of which want to gobble up those seeds
or snap up any tasty germinating seedling.
Your only chance is to get your seeds as far away from yourself
and those pests as possible.
The question is, how do you do it?
There's a clue.
This young orang-utan will grow to be
the heaviest arboreal animal in the world.
And this pygmy elephant will grow to be nearly three metres tall.
By most standards, that's not pygmy.
They both face the same problem...
..how to find enough food.
The solution,
as the baby is starting to realise, is that they never stop moving.
She will have to work hard to keep up with the herd.
You see, these elephants are on the lookout for fruit.
Overhead, orang-utans search for fruit in the canopy.
And thanks to their agility, they can reach almost all of it.
But for the young elephant,
even low-hanging fruit can be just out of reach.
Her mother shows her how to get them.
But what's important here is that this elephant can smell some fruit
from well over a kilometre away.
And there are some plant species here
that have specifically evolved to attract elephants.
For instance, this jackfruit is so large
that nothing else can really deal with it.
His huge gut will take a couple of days to digest that meal,
by which time he may have travelled over ten kilometres.
Between them, the orang-utan and the elephant
disperse thousands of species of fruit.
Not only will the seeds be supplied with ready-made fertilizer,
they will germinate safely away from the threat of attack
from the mother tree's pests.
Rainforests, more than any other ecosystem,
rely on animals to spread their seeds over large distances.
But paradoxically, this has created a nightmare.
It's not often you get the chance to walk 30 metres up in the treetops.
This canopy walkway certainly gives a unique perspective
on the diversity of the rainforest.
It's been built in Sabah in Borneo.
Look at this!
Wow!
There's no doubt that there is a huge range of species here.
But the flipside is that in any given area,
there aren't that many individuals of each of those species.
This tree is just coming into flower.
But the thing is, if I look around the forest here,
I can't see another of these trees.
No.
And this is bound to present a challenge
when it comes to sex, to pollination.
But it's a challenge that nature has risen to.
The simple problem is,
how do you cross-pollinate to fertilize your seeds
if you're all alone?
The methods British trees might use won't work here.
Below the canopy, there's virtually no wind.
And relying on a general pollinator, such as a honeybee,
is a bit like posting a letter without an address.
It might have collected YOUR pollen,
but it's just as likely to deposit it on the wrong flowers.
No, what's required in the rainforest is special delivery.
The nectar in these long flowers is out of the reach of most animals.
Because these petals have evolved in harmony with
a very specific pollinator...
..a sunbird.
With his long bill, he can reach the nectar deep within the flower.
And he needs to get this nectar
because he's evolved to feed on little else.
And critically, when he's had his fill here,
he'll have to find another tree with the same type of flowers.
If you're a tree in a rainforest, this relationship is ideal.
For plants, specialist pollinators act as a form of insurance policy.
You see, these animals have evolved to feed on your flowers
and only your flowers.
So once they've visited you,
no matter how far away your nearest neighbour is,
they'll get there and effect pollination.
And this is typical.
Many of the trees and plants out here will have specialist pollinators.
And because there are thousands of species,
this in turn means that there are a vast array of these types of animal.
The final leg of my journey takes me to Amazonian Peru.
Now we know why jungles are so productive,
so diverse,
I want to see how the whole ecosystem fits together.
There's one series of remarkable relationships
that even in this distant rainforest involves me and you.
Now, you may not know what this is.
But I'm certain you know what this is.
This is a brazil nut.
And this is a brazil nut pod.
So inside here are about 20 of these.
Come down here.
Because quite naturally, this has come from a brazil nut tree.
And here is that tree.
What a thing!
It's magnificent.
Each huge seed pod takes 12 months to grow.
And this mighty tree owes its entire existence
to connections that have taken science years to uncover.
One of the most intricate relationships takes place up there.
I think I've got it.
It's difficult to say, it's so high up.
Now, that is it, that's it.
Yeah.
Well, after a bit of a climb, here's the plant that I was looking for,
and saw from all the way down there on the ground.
It's an orchid.
This little orchid is absolutely essential to the brazil nut.
In fact, if you've ever eaten one yourself,
then you owe a debt of gratitude to these flowers.
The story of why the brazil nut needs the orchid is extraordinary.
It's so wonderful, it's almost beyond belief.
And through unravelling that story,
we can understand some astonishing things.
SAWING
It starts with those amazing-looking seed pods.
How on Earth do they get dispersed?
They're not only very heavy, they're unbelievably tough.
I want to try a little experiment to find out.
All I need is some fishing line and some little pink flags.
I know this might seem a bit odd, but trust me,
this is cutting-edge ecology.
It's all primed and ready for action,
but there are none of the animals around at the moment.
So I'm going to put this down here,
wait for them to sniff it out, and be patient.
Given their size, you might expect something large.
But the animal that can handle it is actually rather small.
It's a rodent called an agouti.
She may look insignificant,
but her actions have a very significant impact
on this rainforest.
She specialises in eating tough seeds and nuts.
Thanks to her teeth, which work like chisels.
So this is how they're meant to be opened!
That nut is packed full of energy and nutrients.
After all, it contains everything you need
to start growing a brazil nut tree.
And what happens next is the bit that I'm really interested in.
Because there are so many nuts in the pod,
she can't eat all of them in one go.
She's saving the rest for later.
The question is, where is she going to put them?
And look at that.
She's even putting every leaf back exactly where she found it.
Each nut is being carefully carried away to a different hiding place.
As far as she is concerned, this is the ideal place for a larder.
And by complete coincidence, as far as the tree is concerned,
this is the ideal place for its seed to germinate.
Here is one of our marked nuts.
And the mother tree is hundreds of metres through there.
So the tree, a plant, has managed to get a mammal to bury its seeds
with just as much care as a really good gardener.
It's one of those magical rainforest relationships.
And the best thing about it is that she has no idea how important she is.
The agouti is the only animal
that can disperse the seeds of the brazil nut tree,
so the brazil nut tree is completely reliant on the agouti.
It's a case of what we call species specific dependency.
Off it goes to bury one of the nuts.
And you know,
I can guarantee that every brazil nut that you've ever cracked open
has come from a tree that was planted by one of these animals.
That's fantastic.
You've got to admit, ecology is fantastic.
It's clear why the brazil nut tree needs an agouti.
But how does the orchid that I found fit into our story?
Like many flowers, it uses pollinating insects, bees.
In fact, these orchids
use a very special group of bees called Euglossine,
or orchid bees.
And more specifically, they have to be males.
Unlike most bees, which are after nectar,
this one is after something quite different.
He's after perfume.
He collects a waxy secretion by rubbing his legs all over the flower.
And in doing so, pollinates that flower.
Collecting this perfume is so important to a male orchid bee
that it may fly miles all over the forest in search of it.
The reason that he's collecting scent
is that the males compete with one another using smell.
They have a sort of a scent-off.
The one with the best bouquet of perfumes
gets the right to mate with the females.
But what has all of this got to do with our story of brazil nut trees
and agoutis?
Only the male orchid bees pollinate the orchids.
To reduce competition between the sexes,
the males and females have evolved different niches.
It's another example of the extreme diversification
that takes place here in the rainforest.
So the females pollinate a completely different species.
A very, very much larger one.
The one that I'm sat on.
The brazil nut tree.
Once a year, the tips of the brazil nut tree branches
are adorned with large white flowers.
They attract insects from all over the forest.
Including the much larger female orchid bees.
The nectar is hidden beneath a special petal.
And the female orchid bees
are one of the few insects that are big enough
and strong enough to open the flowers.
This smaller bee, on the other hand,
simply doesn't have the strength to open it.
This selective door policy
is the tree's way of ensuring that it will only be used
by insects which are guaranteed to visit other brazil nut tree blooms
and then pollinate them.
The intricate relationship between the male orchid bee and the flowers
is the reason that brazil nut trees like this one
can only grow in intact rainforest ecosystems.
Now, the brazil nut tree needs the agouti,
way down there, to disperse the seeds.
The agouti needs the female orchid bee up here to pollinate the flowers
so those seeds are produced in the first place.
The female orchid bee needs the male,
which in turn needs those orchid flowers.
That's why the brazil nut needs the orchid.
You just couldn't make it up, could you?
This wonderfully complex web of connections has all come about
due to the sheer biodiversity of rainforests.
And understanding it
reveals the natural world in a very different light.
Animals don't simply live in forests.
They are the forests.
And forests without orang-utans and elephants are broken ecosystems.
We might want to save rainforests for the elephants,
when, really, we should be saving the elephants for the forest.
We've been motivated by what an orang-utan looks like.
We should be motivated by what it does.
Stretched out around me is the most complex ecosystem on our planet,
home to millions of different species.
And whilst there's wonder in the detail of their individual lives,
nothing competes with the sheer beauty of the bigger picture.
The dynamic, functional, living, breathing rainforest.
For me, science is the art of understanding truth and beauty.
Well, here's the beauty.
And we've seen just a little of its truth.
If you'd like to know more
about the fascinating web of links between species,
the Open University has produced some material
both to inform and inspire you.
For your free copy,
or to find out more about Open University programmes, ring...
Or go to the website...
And then follow the links to Open University.
And join me next time,
when I'll be travelling to some of the world's greatest grasslands.
Subtitles by Red Bee Media Ltd.