Yellowstone Nature's Microworlds

living puzzle in the universe.

..untangle their interlocking pieces

each of Nature's Microworlds.

Rocky Mountains of North America

Its unique geology means that

volcanic heat from the Earth's core comes right to the surface.

Established in 1872, Yellowstone is the world's first national park,

its awe-inspiring landscape,

it's home to an array of North America's most charismatic wildlife.

These dwell in vast forests

Isolated by sheer mountain peaks,

is a stage upon which scientists

discovered surprising connections

To fully understand the key to the rich complexity of life

in Yellowstone today, we must look at how the presence of one animal

can affect that of another.

At the very top of the food chain

to 98 wolves, in ten packs.

the herds of large grazing mammals.

At the other end of the spectrum

live very independent lives.

This was discovered after the National Parks and Wildlife Service

launched a landmark project

from the park for 70 years.

They were eradicated as part of a predator control campaign

The releases were surrounded

Some parties claimed that wolves would unleashed devastation

of America's rare grazing mammals.

Soon after the reintroduction

took a turn for the better.

..and numbers of water birds

This improvement in river habitat

was down to the tireless work

their precious reserves of water

dry summers and remove sediments.

The timing of the beavers' return

between wolves and beavers?

How are their lives interconnected?

Before we answer these questions,

a force to be reckoned with.

standing 1.5 metres at the shoulder, and weighing over 300 kilos.

only weighs about 50 kilos.

have the advantage of numbers

Despite the wolves' apparent advantage, the elk is in his prime.

will not risk following him

he makes good his escape...

..to the disappointment of the pack.

A wolf pack is a close family unit.

Pack hierarchy is maintained through these ritualised play-fights.

Rank is based on attitude rather

And there is one other way through which they strengthen their bond.

It maintains cohesion within the pack, even if they are separated.

it advertises their presence,

and letting other wolf packs

Apart from the fact that beavers exist within wolf territory,

they have little to do with them.

have their numbers increased?

at what Yellowstone was like

before the wolves were brought back.

Before 1995, Yellowstone's top dog

Yellowstone had the largest coyote population in North America.

Yellowstone's coyotes are less than half the size of the wolves

They exist mainly on a diet

But, during the reign of the coyote,

Thievery is another coyote trait.

their hard-earned winter catch

in a burrow under deep snow.

The coyote's excellent sense

This fearlessness had a devastating impact on the wider ecosystem.

But what they lack in height,

Coyotes are not big or fast enough

the average life expectancy of a pronghorn fawn was just 35 days.

and the pronghorn population fell

By the early 1990s, there was serious concern for the pronghorn.

But all that was to change.

coyotes were dealt a shocking blow.

Wolves pay little attention to them.

substantial enough to feed a pack.

has seen pronghorn numbers increase

to being more secretive and nervous.

over their shoulder at every turn.

So by, policing the coyotes,

Were coyotes also the reason why beavers were absent in Yellowstone?

the same material, known as a lodge.

The lodge can only be accessed via an underwater entrance.

Inside, safe from the attention

relationship with the wolf?

They will sometimes dig open beaver lodges and prey upon beavers.

of chasing big prey like elk.

Despite their enormous bulk, bears are surprisingly fast.

However, bears are also quite happy to let someone else do all the work.

all of their kill in one sitting,

the carcass becomes an abandoned picnic just waiting to be exploited.

only the hardest winters would bring

the supply has not only increased

bears are more than capable

Fear of wolves is most definitely

Despite strength in numbers, wolves know to respect bears -

and powerful claws mean business.

wolves will eat at the same table.

an unlikely bounty to Yellowstone.

the bear population is on the up.

If bear predation had any impact

we'd not expect beaver numbers to increase alongside bears'.

to the return of the beaver.

What other wolf relationships

to an increase in beaver numbers?

Bulls can weigh over 1,000 kilos.

stand their ground against a pack.

These giants have been roaming the plains of North America

They can also slow their metabolism

to reach the grass beneath.

It's estimated that 50 million bison once lived in North America...

before Europeans settled here.

Overharvesting caused total numbers across the continent to crash

to less than 2,000 in 1900.

Now, thanks to careful management, their numbers across North America

have anything to fear from wolves.

But, during the summer months, it's the young that are most vulnerable.

it's still a risky business.

the calves from their mothers.

But the bison are quick to react.

A large bull joins the fray.

Any attempt at snatching a calf

fatal consequences for a wolf.

they've missed their chance.

The threat of serious injury or death is always a good deterrent.

They must be successful soon,

for they themselves have young to rear at this time of year.

to be seen out in the open.

all of their time in the den,

they'll soon rule themselves.

Breeding success in wolves is strongly linked to hunting success.

If their kill rate declines, then the wolf population soon follows.

Bison provide plenty of meat

pushes wolves to their limits.

Because of this, bison are not

With bison numbers changing little in response to wolves,

and river habitat within the park.

But there is one prey animal that's

Numbering tens of thousands,

elk are the most numerous grazer

to advertise his status to females

and to other males in the vicinity.

are a sign of age and status.

But there are challengers to the throne and he must prove his worth.

and intimidate an opponent.

Fights may last many minutes.

the competition is seen off...

A large male may not eat for weeks

And, if he's lucky, he'll mate with

he has very little time to feed

and regain condition before thick snow covers the lands once again.

the elk population consists

and elk are interdependent.

grazed in open country without fear.

And here lies the key to our puzzle.

Without fear of predation by wolves,

Especially on the river banks where everything was grazed to the ground.

and never gained a foothold.

strengthening the riverbanks,

by the trampling of the herds.

the water-holding properties of the soil are diminished.

This in turn encourages silt to build up in fish spawning beds.

As a whole, biodiversity decreased.

Yellowstone was left with less habitat for birds and insects,

The culture of fear instilled

to their naturally flighty state.

Instead, the herds stay on the move.

vegetation once chewed to its roots

Willows, aspen and cottonwood trees started to re-colonise river banks.

for much of Yellowstone's wildlife.

These, in turn, provide food

which themselves provide food

The enriched soil encourages

This provides a much better habitat

And fish provide an important

a far more beneficial impact

all levels of the food chain.

one of Earth's great microworlds.