3 Animals That Keep Their Whole Ecosystem Together

The original keystone refers to a wedge-shaped
slab at the peak of a stone arch.

If you remove the keystone, you risk the whole
thing tumbling down.

And some ecosystems work the same way, relying
on one keystone species.

In biology, keystone species have a disproportionately
large impact on their habitat, given their

size or numbers.

Their daily activities affect all kinds of
other species, directly or indirectly.

And a change in their number can cause a trophic
cascade, where effects ripple throughout the

ecosystem, often in surprising ways.

Take the grey wolves of Yellowstone National
Park in Wyoming.

Their numbers dropped to zero around the early
1930s, mostly because of hunting.

But in 1995, wolves were reintroduced to the
park, and the wolves’ impact has been monitored

ever since.

Turns out, that impact is seriously important.

The wolves’ absence and reintroduction changed
Yellowstone in large and often surprising

ways, right down to how the rivers flow.

For one thing, wolves prey on elk — and
the elk know it!

So their behavior changes when wolves are
in the area.

Elk are generally nomadic, staying on the
move as they munch on plants.

But without any wolves around, the elk became
much less cautious, preferring to settle down

and eat a lot in one place at a time.

The elk even ate all the way down to the riverbank
– somewhere they wouldn’t normally dare

linger if there were wolves around.

Instead of eating a little bit from lots of
different plants, they ate so much at a time

that aspen and cottonwood trees declined,
and so did the riverside willows that beavers

and some songbirds depend on.

And beavers are also keystone species, because
of their special engineering talents.

Their dams slow the flow of rivers, preventing
floods and offering a wide range of habitats

for all kinds of species.

Ever since wolves were reintroduced to Yellowstone,

willows have grown better, beaver colonies
have increased from just one to nine, and

songbirds are flourishing too.

Elk numbers declined at first, but now seem
to have stabilized.

And bison numbers are up, probably because
of a decrease in competition from the elk.

Research is ongoing to assess the wolves’
long-term impact, considering the many subtle

interconnections in this complex ecosystem.

But as top predators, it’s clear that the
presence, absence, and reintroduction of wolves

has resonated throughout Yellowstone.

And research into other wolf habitats will
help work out what’s unique to Yellowstone

and what can be applied elsewhere.

Elephants also do a lot to manage their environment
— from what goes on in their mouths, to

what comes out the other end.

They’re sometimes known as the “mega-gardeners
of the forest”.

For example, without African Forest elephants,
a single species of acacia tree tends to dominate

in African forests.

It grows fast and shuts out the light from
other plants.

And the elephants help counter that.

They sometimes knock down acacia in their
search for food, opening up space and a critical

shaft for light.

Other plant species seize their chance, adding
to the forest’s biodiversity.

The smaller branches they knock down provide
hidey-holes for lizards, which are more diverse

in places where elephants roam.

When reaching for leaves or fruit, they’ll
often knock off a bunch more.

And these windfalls get picked up by smaller
ground-dwellers like warthogs, as well as

kudu, which is a type of antelope.

All this eating results in plenty of dung
– around a metric ton every week.

And all that poop becomes a mini-ecosystem
all by itself, since it’s rich in nutrients

the elephants couldn’t process.

Fungi live in it, as do insects like beetle
larvae, crickets and spiders.

In 2009, three species of frog were found
happily living in Asian elephant dung.

And of course, it’s excellent fertilizer.

Many plant species grow better in elephant
dung than in poop from any other animal.

Their wide roaming and variation in movements
make them especially good at spreading seeds

to new places.

But you don’t have to be as big as an elephant
to have a jumbo-sized impact on your ecosystem.

Parrotfish are named for their tough, almost
beak-like mouthparts.

These hardened lips are well adapted for plucking
algae off coral, their main food source in

their warm reef environment.

It may not be glamorous, but it turns out
to be vital to keeping the reef healthy.

Without parrotfish, macroalgae can smother
the coral to the point of killing it off.

And no coral means no reef, which would be
big trouble for the species that call coral

reefs home.

A major report covering four decades of research
in the Caribbean identified parrotfish as

a group to keep a special eye on.

Coral reefs are generally having a tough time
of it: with climate change, ocean acidification

and pollution steadily degrading the ecosystem.

The parrotfish’s maintenance work helps
keep reefs resilient, so they can recover

from blows like sudden heating or a hurricane.

Caribbean reefs where parrotfish are heavily
fished are suffering

the most.

So, Like all keystone species, they really
hold their ecosystems together.

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