Original subtitles

In the vastness of the Pacific, there's a place unlike any other.

Enchanted volcanic islands that are home to a remarkable

collection of animals and plants.

Here, evolution is proceeding at extraordinary speed.

Galapagos.

A place of wonders.

Millions of years ago,

the islands were colonised by a strange cast of characters.

But to settle in this harsh, unforgiving landscape,

those new arrivals had to dramatically adapt their bodies.

Today, revelatory discoveries are still being made about them.

And from their story, we can piece together how Galapagos

came to be one of the most diverse environments on our planet.

It's perhaps surprising that the Galapagos should have become famous

for its biodiversity,

for the fact is that living conditions here are very tough.

On the equator, the heat is intense. There's very little water.

Much of the land is covered by bare volcanic rock.

And yet, every species that lives here

is descended from an ancestor from the continents

that have taken on these conditions and won.

And the way in which they did so is extraordinary.

The total land area of the 16 islands and rocky outcrops

that make up Galapagos is less than half that of Wales.

Yet, for its size,

there are more unique species here than anywhere else on Earth.

Why should that be?

There are clues hidden within the landscape.

This crescent-shape strip of cliff,

rising steeply from the Pacific Ocean, is the island of Tortuga.

And like all the Galapagos Islands,

it's a wonderful place to see wildlife.

Here and there, there's a sea lion.

Above that, nesting seabirds.

Boobies and Galapagos gulls.

But you only really appreciate the true character of this island

from the air.

From here,

it's clear that this is the last fragment of an extinct volcano.

These curving cliffs are all that remains of what was once

a completely circular crater.

And that's an indication of something very significant

about all these islands.

They change with enormous rapidity.

The history of these islands is very much the same.

Each is born on the bottom of the sea,

and rises up through the waters to emerge as a volcano.

(VOLCANO BLASTS)

This is a typical Galapagos island in its infancy.

But then, after a million years of eruptions,

volcanic activity ceases.

Two million years after its first appearance,

the island is approaching middle age.

It has a moist climate and is covered by forest.

It begins to sink under its own weight of ash and lava.

It's battered by erosion, and after four million years,

it's near the end of its existence.

Low-lying and arid with little rainfall,

it's surrounded by beaches of soft sand.

The waves and rain continue to take their toll,

until all that's left is a craggy outcrop of rock.

These islands, in geological terms, are very short-lived.

Today, there are islands in the Galapagos archipelago

that illustrate every stage in this history.

The youngest in the west are arid, black and still breathing fire.

The oldest in the east have long since ceased to erupt.

But each island provides its colonists with a range of habitats.

And it's the youngest active islands that pose the greatest problems

for any animals that attempt to colonise them.

In the far west of the archipelago lies Fernandina.

This is the youngest of the Galapagos Islands.

It's forbiddingly desolate and inhospitable.

But one animal has colonised its shoreline.

This creature is a specialist at surviving in this harsh terrain.

And, in adapting to this place,

it has become like no other animal on Earth.

Behold the marine iguana.

The ancestors of these iguanas almost certainly

lived in the jungles of Central America.

There still today you can see iguanas in the trees

overhanging the rivers, nibbling leaves, or on rafts of reeds.

Just occasionally, some are swept out to sea,

and the vast majority of course die there.

But just a few, a long time ago, were fortunate enough to be swept

by a favourable current out to the ocean and pitched up here.

In their ancestral rainforest habitat, iguanas are vegetarians.

(IGUANA GROWLS)

Here, they browse on juicy leaves.

But the iguanas that first appeared in the Galapagos

could find no such things.

So these iguanas, to survive,

had to eat the only kind of leaf that was available.

Seaweed.

And to get the best of that,

they had to do something even more radical.

They had to swim.

They even learned to dive.

They acquired the ability to hold their breath for up to an hour

so that they could swim down to a depth of 20 metres.

Their claws strengthened,

so they could cling to the rocks on the seabed.

And under the water, they found an endless supply of seaweed

which grew in abundance in the nutrient-rich currents

that flow around the islands.

But that was not all.

Their snouts became flatter to help them graze.

And their teeth became sharper to grip the slippery seaweed.

But cold water can be dangerous for cold-blooded reptiles.

After a few minutes feeding at sea, the iguanas are seriously chilled

and in urgent need of a warm-up.

And their skin enables them to get that.

It is black.

Dark objects absorb heat and each scale in the marine iguana's skin

is like an element in a miniature solar panel.

Now all a marine iguana needs to do

to bring its body back up to temperature

is to bask in the hot equatorial sun for an hour or two.

But eating nothing but seaweed creates another problem -

too much salt.

The marine iguanas dealt with that in a very particular way.

They evolved a special gland in their nose.

They simply sneeze the excess salt from their blood.

These changes had to happen very quickly in evolutionary terms

if the iguanas were to survive.

But here, conditions sometimes change.

And then, even iguanas struggle to keep up.

Every three to seven years,

the weather becomes very extreme and irregular.

It's a phenomenon called El Nino.

And it can have a devastating effect on wildlife.

Evolutionary biologist Maren Vitousek

has studied the effects of El Nino on the Galapagos marine iguanas.

She discovered that it decimates their food.

Pressed as 1.0.

Marine iguanas usually eat red and green algae, and that algae

dies off completely during El Ninos, during strong El Ninos.

And it's replaced by a brown algae.

Marine iguanas aren't able to digest the brown algae,

so they eat it, but it sits in their stomach, basically in a big lump.

And so you can find iguanas dead on the beach of starvation

with stomachs full of this brown algae that they just can't digest.

The marine iguana is worst-affected of all Galapagos animals

during an El Nino.

As many as 90% of them can perish.

It's bad news for iguanas...

...but good news for scavengers.

And new research has shown that the iguanas have evolved

a special ability that enables them to survive the famine.

Their bodies shrink.

They lose not just fat and muscle, but bone.

The iguanas can actively reduce their skeletons

over just a few months.

So we saw that the largest animals were decreasing their body length

by as much as 20%.

And the magnitude of that means that it can't be simply that they're

changing their cartilage or connective tissue

or resorbing muscles.

Those things together count for about 10% of length.

So, instead, 20% of shrinkage really indicates that it's got to be

the skeleton itself that's decreasing in length.

This amazing ability to do reabsorb bone in times of hardship

is unique to these reptiles.

It's most recent discovery in understanding how marine iguanas

managed to survive on the coastlines of the youngest Galapagos Islands.

But iguanas were not alone

in adapting to these desolate volcanic shores.

This is the lava heron.

It's well camouflaged.

It's grey feathers make it relatively inconspicuous

against the blackened lava rocks.

So, moving stealthily, it can hunt very effectively.

Its favourite prey is the Sally Lightfoot crab,

whose striking red shell stands out against the jet-black lava.

But the adult crabs have tough shells and sharp pincers

and herons know better than to attack a full-grown one.

Juvenile crabs will be a much more attractive prospect.

But they have responded to the landscape of Fernandina.

They have black shells that make them far less conspicuous

to prowling herons.

This time, the lava heron

will have to make do with a really tiny snack -

a Sally Lightfoot hatchling.

On the shorelines of this infant Galapagos island,

life is tough.

Habitats are limited.

Opportunities are scarce.

But away from the coast, survival is almost impossible.

There, it's too dry and too hot for most forms of life.

But, in time, that will change.

As the island ages,

this hostile landscape will become a little more welcoming.

It will one day support a rich forest,

full of new places for animals to live.

This change is driven by the volcanic hotspot

which brought the island into existence.

The eruptions continue.

95% of its final bulk will accumulate

in the next few hundred thousand years.

By the time the eruptions have ceased,

it's grown so large that it has acquired a new power.

It has the ability to create its own weather.

Humid, oceanic winds blowing across the Pacific

hit this mountain of lava and are so forced upwards.

That caused them so that they can no longer hold their load of moisture,

and it condenses as mist and rain.

And that allows plants to thrive.

Santa Cruz, in the centre of the archipelago,

is typical of these middle-aged islands.

(THUNDER RUMBLES)

Its slopes are covered by a mantle of green.

This might seem to be a forest of giant trees supporting a rich

population of animals of all kinds.

But, this being Galapagos, this forest is different.

These plants are not true trees.

Trees tend to have big seeds,

and few of those made it across the oceans to the Galapagos,

and certainly none up here into the highlands.

But smaller plants have smaller seeds.

Some, so small they can float on the wind.

And one member of the dandelion family made it up here.

And without competition from other trees, they grew big.

This, you could say, is a forest of giant dandelions.

This very special kind of dandelion is called scalesia.

It's unique to the Galapagos, and flourishes on the high slopes

of Santa Cruz and other middle-aged islands.

It's become the host for a whole community

that could not exist without it.

Because scalesia performs a conjuring trick that gives life

to the rest of the forest.

There's no ground water in these thin, volcanic soils,

but the scalesia trees are tall enough to collect moisture

from the sky - from clouds and from mist -

and that is sufficient to sustain

a whole community of plants and animals.

High in the canopy, mist condenses on the spindly,

crisscrossed branches of the scalesia.

Water trickles down their wooded trunks.

Ferns root themselves in the damp moss that clings to their bark.

The moisture creates conditions where spiders

and other small creatures can live.

And on the forest floor, pools appear.

Here, dragonflies thrive and, once again,

they belong to a species that occurs nowhere else but here.

But the Galapagos climate is changeable

and the mists sometimes dry up,

leaving this delicate ecosystem

exposed to the burning equatorial heat.

Some trees, however, have evolved a way of protecting themselves.

This tree has developed a mutually beneficial relationship

with the lichen that grows on it.

The lichen shields the tree from the sun,

preventing it from getting scorched.

And the tree provides the lichen with moisture and nutriment.

But if the weather gets really sunny

then the lichen shrivels

and stops taking nutriment and moisture from the tree

but, at the same time, still prevents it from getting sunburnt.

And when the moisture returns, the lichen can grow back.

So, plant and lichen make the best of the two extremes of climate.

Fresh water anywhere on land creates opportunities.

But on volcanic islands like Galapagos,

it gets to some very strange places.

Deep in the rocks beneath the scalesia forest

there is a network of hundreds of tunnels called lava tubes.

Here, the species-transforming power of the Galapagos

is as active as everywhere else.

For scientists like caver Aaron Addison and biologist Steve Taylor,

these lava tubes are the Galapagos Islands' new frontier of discovery.

It's difficult to imagine or indeed believe that there are still

such untouched areas within a place that's so well-known

as the Galapagos and so well studied.

But we do find those areas, and those areas then lead us

to a new species that are unknown to science,

that haven't been described by anyone else, ever.

Black volcanic rock still lies only a few inches down

beneath the forest trees of Santa Cruz.

It erupted millions of years ago and flowed down the sides

of the volcano in rivers of molten, red-hot lava.

As the surface of the lava cooled,

it solidified and formed a rocky skin.

And when the eruption ceased, liquid lava continued to flow away,

leaving behind these huge, empty caverns.

And now, a constant trickle of life-giving water

drips down into the winding tunnels.

Steve Taylor is an expert on underground life.

The subterranean world is full of surprises.

It's just really exciting, cos these animals are pale and eyeless.

There's no selective pressure to maintain eyes in a cave,

so they're blind.

And they often have elongated appendages

so they can either find prey or avoid prey.

This amblypygid, half-scorpion, half-spider,

is a predator and a scavenger.

It might seem ungainly, but it's well adapted to this black habitat.

Eyes are useless down here, and it's become almost blind.

Instead, it feels its way through the cave

with great skill and sensitivity.

Two of its eight legs are greatly elongated

and capable of extending to twice the length of its body.

This millipede has lost all its colour.

Why spend precious energy creating a pigment in a place where

no-one can see it?

Spiders, too, haunt the lava tubes.

And just like the tortoises and iguanas,

these creatures have evolved into many different species.

There are 90 of them, all unique to the Galapagos.

But spiders don't just differ from island to island.

They do so dramatically, even within a single lava tube.

Some that have been here for a long time are blind

and feel their way through the cave.

A few have lost their eyes entirely.

But living just centimetres from them are more recent colonists,

species that still retain their eyes.

Such variety in such a small area seems extraordinary,

but in the Galapagos, it's almost common.

The huge number of differing habitats has made Santa Cruz

a centre of biological diversity.

And, as an island ages, so it develops more habitats.

Now, it's entering its old age.

It's no longer growing.

The sheer mass is too heavy for the earth's crust to support.

It begins to sink under its own weight.

And now, the rainwater that has been falling on it throughout

its middle age begins to carve away its substance.

So the island becomes smaller, drier and flatter.

That is what has happened to Espanola.

It's nearing four million years old.

Its forests have gone.

But it now has a different range of habitats.

Millions of years of erosion have created beaches of soft sand.

And they suit some animals very well.

This is a natural bathing beach for Galapagos sea lions.

They are just one of the very few mammal species that are unique

to the Galapagos.

And the beach of an ageing island

provides them with an excellent nursery.

Here, sea lion pups can suckle in complete safety.

Though they can be a little irritating.

And, in a protected cove close by the beach,

parents can teach their youngsters to swim.

After a swimming lesson, the beach is a perfect place to relax.

Sea lions seem to have an idyllic life,

but there is just one irritant...

(FLIES BUZZ)

...flies.

On younger islands with rocky coastlines,

sea lions have help to keep the flies at bay - lava lizards.

(FLY BUZZES)

But on the sandy beaches of Espanola,

the lava lizards are nowhere to be seen.

They prefer the nearby rocks, which are warmer.

So here the sea lions must deal with the fly problem by themselves.

Espanola's soft sand beaches

are also gratefully valued by another species -

the waved albatross.

The islands provides an excellent nesting ground

for these huge seabirds.

With a wingspan of two-and-a-half metres,

the albatross is so big and heavy

that it has to get up a considerable ground speed in order to take off.

And that's what the beach provides.

As you might expect, the species of albatross that lives here

is slightly different from those found in other parts of the world.

These wavelike patterns on its neck feathers distinguish it

from all other albatross species.

All albatrosses spend most of their lives on the wing,

travelling across entire oceans.

But here on Espanola, the waved albatrosses can nest.

(SQUAWKING)

The isolation of the Galapagos and the protected soft shingle beaches

of Espanola make this ageing island

an excellent breeding ground for them.

35,000 settle here each year.

Waved albatrosses are monogamous - they mate for life.

But how do you find a new mate or recognise your old partner

in such a crowded colony?

You dance.

(RHYTHMIC SQUAWKING)

The whole performance can last for nearly an hour.

And it's repeated several times every day.

Sometimes, a potential rival steps in to try his luck.

The female in the middle dances with both enthusiastic males

at the same time.

The reward for the victorious male is great.

A mate.

And an opportunity to pass on his genes.

The many habitats of Espanola and all ageing Galapagos Islands

were created by the erosive power of sea and weather.

But erosion can have only one final result.

Destruction.

So, a Galapagos island worn down by the waves and the weather

eventually reaches the last stage of its existence.

After millions of years sustaining life,

all that remains of it above water is a rocky, curving cliff.

Like Tortuga.

There are many relic islands like Tortuga in the Galapagos.

Devil's Crown in the south of the archipelago is even closer

to disappearing altogether below the waves.

But even in its final days,

a Galapagos island provides a habitat for some.

Its rock has been turned by erosion into sediment, and now,

that fertilises the marine life around its submerged remains.

A ring of coral two metres wide encircles its dwindling stump.

So, a whole new animal community develops.

Corals are at its centre.

Bristle worms hide inside them,

occasionally emerging to browse on passing morsels.

Fish find safety among the branches.

And some of the species, once again, are unique to the Galapagos.

The reef teems with life.

But the presence of warm water corals here in the Galapagos seas

is something of a surprise.

Because penguins that need cold water live here too.

So how can tropical corals and penguins co-exist?

The Galapagos Islands have one more trick up their sleeve.

The archipelago lies at the confluence

of several deep ocean currents.

And that creates a bizarre mixture of marine habitats.

The subantarctic Humboldt Current flows around the islands

and chills the water just enough for the penguins to survive.

The corals can't grow in such cold water

but they can go into a state of semi-hibernation for short periods.

When warm water from Central America is dominant,

the temperature rises by about seven degrees.

Now the corals can grow...

...and the penguins can find refuge

in the few remaining pockets of cold water in the coves and bays

that still remain.

So, even in the last stages of its life,

a Galapagos island can support a rich animal community.

But remarkably, even this is not the end of the story.

Because even when an island totally disappears beneath the waves,

it continues to influence life in the surrounding seas.

The remains of ancient Galapagos islands

stretch for hundreds of miles across the Pacific seabed.

These were once volcanoes like Fernandina,

vegetated mountains like Santa Cruz

and low-lying nurseries like Espanola.

Today, those environments are long gone,

but the remnants of the islands under the sea are still key

in the lives of one of the ocean's most magnificent inhabitants.

Up to 12 metres long, it's the largest fish in the world.

The whale shark.

Whale sharks come to the Galapagos in large numbers

at the same time every year.

But why they do so is a mystery.

Marine biologists Alex Hearn and Jonathan Green have spent

the last five years trying to solve the puzzle.

If you think about how Galapagos is formed and how currents work,

the most productive waters are actually out west,

so you would've thought that if whale sharks were here to feed,

they'd be out in the west of the archipelago, and they're not.

They're up north.

So, why are they coming here? It's clearly not to feed.

What we found out recently is that it's mainly large, pregnant females.

Are they coming here to give birth?

This may be the pupping ground for whale sharks. I'm slightly sceptical.

I think we'd have seen juveniles, and we don't.

So, that brings back the question, well, then,

if they aren't pupping here and they aren't feeding here,

why are they coming?

To understand the whale sharks' migratory patterns,

Hearn and Green attach satellite tags to the sharks they encounter.

This enables them to track their movements.

And it's revealing some extraordinary new facts.

First, the sharks swim open-mouthed through the rich waters

off the west coast of South America.

Then they continue their journey westwards to the Galapagos.

But they only spend a few days at a time in the islands' waters,

before continuing westwards out into the open ocean.

Nobody has yet proved why the whale sharks do this,

but Alex Hearn has begun to formulate some ideas.

I think there are two possibilities.

Firstly, they may be using Galapagos as a waypoint which directs them

towards their pupping grounds.

The other option is Galapagos may be providing a service along way,

and that service may be cleaning,

because we do see a lot of cleaning behaviour from the reef fish,

or it may be a combination of the two.

The long line of submerged Galapagos islands could play a central role

in the whale sharks' extraordinary journey.

It might be that they serve as signposts

by which the sharks navigate.

If you start looking at where they're going,

especially the tracks that we have, along those ridges

and then up to the next ridge and back down again, it certainly

seems that they're associating with those ridges for one reason

or another, and that could be geomagnetism or it could also be

something to do with the biology of the water column above the ridges,

but certainly something is going on.

From their birth to their death,

the islands have acted like evolutionary pressure cookers.

From the youngest islands like Fernandina,

middle-aged ones like Santa Cruz and the old islands like Espanola...

...they are extremely varied, with contrasted conditions.

Deserts, rainforests and polar waters crowded together

in a very small area.

These huge variations have created a wide range of opportunities

for the few animals that have managed to reach here.

As they colonised...

...so they adapted.

And consequently, flourished.

That explains many of the oddities of the inhabitants of these islands.

Including that most fundamental phenomenon of all -

the appearance of new species.

The giant tortoise is the very emblem of the Galapagos,

and in their heyday, there were hundreds of thousands of them.

Not only that, there were 15 different species

each in its own locality.

But why should there be so many species

within such a comparatively restricted area?

In the next programme, we'll look at the deep geological forces

that can make a single species produce many,

and turn the Galapagos into this wonderland.

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