Why we simply must have predators

ALERT member John Terborgh is a scientist of enormous stature, whose many accomplishments include a rare MacArthur 'Genius' Award.  Here he tells us why predators are so crucial for the Earth -- a lesson with big implications for understanding nature and our future:

Amur Leopard -- just 70 left in the wild today.

Amur Leopard -- just 70 left in the wild today.

Forty-five years ago, three leading ecologists asked a question of child-like simplicity, “Why is the world green?”

We take a green world for granted, yet this deceptively simple question goes to the very heart of how ecosystems work.

The world is green, the trio argued, because predators limit the numbers of herbivores, thereby protecting plants and allowing them to flourish.

At the time this idea was floated, other ecologists were busy discovering that plants manufacture a potent arsenal of chemical compounds to deter herbivores -- everything from deadly toxins to chemicals that make them hard to digest. 

Far from being helpless, these other ecologists argued, plants actively defend themselves, and this keeps herbivore numbers down.  Under this scenario, predators aren't really needed to keep the world green.  

Who is right?  In theory, it should be simple to find out: just remove the predators from an ecosystem and see what happens. 

Wolves -- widely persecuted but trying to make a comeback in parts of North America and Europe.

Wolves -- widely persecuted but trying to make a comeback in parts of North America and Europe.

But it's one thing to remove little predators such as insects and spiders.  Getting rid of big predators, such as wolves, lions, or jaguars, is a far taller task.  To perform such an experiment properly, one would need to fence off huge areas, some with predators and prey, some with prey alone, and others with neither. 

The cost of such an ambitious experiment would be so high that, to this day, nobody has tried it.  As a result, ecologists are still arguing about why the world is green.

An Accidental Experiment

But purely by accident, an unplanned experiment in Venezuela created the right conditions to test the 'Green World' hypothesis.  There, a massive expanse of forest flooded by a hydroelectric dam created hundreds of artificial islands.  The smallest islands were barely the size of a tennis court; the biggest, at hundreds of hectares, would span a dozen large golf courses.

My students, colleagues, and I studied these islands for 14 years.  And what we found is enormously exciting -- and scary.

The largest islands had enough habitat to support both predators and their prey.  But as island size declined, fewer and fewer species of predator remained.  Once below 10 hectares in size -- equivalent to about 20 football fields -- the predators vanished entirely. 

The Harpy -- king of eagles.

The Harpy -- king of eagles.

At this point you have an ecosystem with a few species of herbivores -- particularly howler monkeys, an iguana, a type of tortoise, and leaf-cutter ants -- but nothing to eat them.

With little to keep herbivores in check, did these islands stay gloriously green, or collapse ecologically?  

Ecological Collapse

What we observed was ecological chaos.  Herbivores attacked foliage in all parts of the forest. The first plants to be killed were seedlings, cut up and carried away by leaf-cutter ants, while howler monkeys and iguanas defoliated trees and vines in the canopy.

Without predators, leaf-cutter ants can decimate a forest.

Without predators, leaf-cutter ants can decimate a forest.

Small saplings were the next to disappear under the herbivore onslaught, followed by larger saplings and woody vines.  Finally, after a decade or more, big canopy trees began to die, standing leafless, ghost-like.

By the end of our study, the once-verdant forest was a degraded tangle of shrubs and vines -- a pathetic vestige of their original diversity.

And while herbivores had won, they ultimately brought about their own self-destruction.  In the end, the decimated islands barely sustained any life at all.

The trio of ecologists -- the architects of the 'Green World' hypothesis -- were right.  We need predators to keep our planet verdant and healthy, and to maintain biodiversity.

Alternative States

The 'alternative state' of a predator-free island is alarming.  Equally worrisome is that we can get there in a variety of ways.  Killing off predators is one way -- and we humans are very good at doing that.

Another way is flooding an ecosystem with nutrients, a process called "eutrophication".  This can happen, for example, if we carelessly use farming fertilizers, which then leach into waterways and other ecosystems.  Biodiversity depends on a balance, and tip that balance too far one way and nutrient-loving species dominate while excluding many other species.

Depressing 'alternative states' can arise for other reasons too, such as disrupting natural fire regimes or introducing exotic species that fundamentally change ecosystems.

But for me, the widespread decimation of predators is the most worrisome way that we are disrupting the natural world.  For that reason, I strongly support efforts to 're-wild' ecosystems -- to reintroduce big carnivores such as wolves, grizzy bears, and tigers to regions where they once held sway.  

Arctic fox in the summer.

Arctic fox in the summer.

Rewilding sizable parts of the world will not be easy.  There are many who will object -- out of fear or ignorance or potential risks to their livelihoods. 

But the world needs predators.  I have been studying nature for a long time, and one thing I have learned is that biodiversity utterly depends on them.

Bringing the science we need to maturity and explaining it to policymakers and the public is a vital goal for our next generation of conservationists.


Will tigers survive in India?

ALERT member Jean-Philippe Puyravaud shares with us his views on tiger populations in India.  Once the dominant predator across much of Asia, the tiger today survives in just a tiny fraction of its former geographic range -- and with just a tiny fraction of its former numbers.

An Indian tiger  (photo by Priya Davidar)

An Indian tiger (photo by Priya Davidar)

The latest tiger census in India shows that the number of tigers has increased, by nearly one-third. 

That is good news, indeed, because India is crucial for tigers.  The country sustains about 70% of the world's tigers but with only 25% of the world's remaining tiger habit.

This excellent result could be attributed to the interest and commitment of the people of India towards their natural heritage, the protection provided by the Forest Department, the efforts of scientists, and the enormous contribution of conservation organizations.

These findings should be celebrated and emulated in richer countries who talk about eradicating wolves -- such as Canada -- or decommissioning nature reserves -- such as Australia.

The finding that tigers have evidently increased has sparked a lot of reaction.  Journalists have celebrated the fact that the tiger is “saved”.   On the basis of the good news, the pro-development Government of India has wasted little time while proposing to build four-lane highways through several tiger reserves.

But is the tiger in India really safe?  To illustrate, I made a graph with 150,000 tigers -- a plausible number -- at the dawn of the Indian Civilization.  Ignore the massacres by British trophy hunters and imagine a smooth decrease of the tiger population over the past 3,000 years.

Tiger numbers fell to an all-time low in 2006 and have increased marginally over the past decade.  What overall trend do you see?

India's catastrophic decline in tiger numbers

India's catastrophic decline in tiger numbers

The recent increase in tiger abundance -– in spite of being good news -- is effectively invisible.

I am not a proponent of “repopulating” India with tigers, but what the graph suggests is that unless the tiger population recovers to several thousand individuals, the species is still tremendously vulnerable in India.

And if this is the status of tigers in India -- which sustains seven-tenths of the global population -- how will it fare elsewhere?

We should celebrate the good news that tiger populations in India have made a marginal recovery. 

But let's not forget that the species is still staring into the abyss -- the victim of catastrophic declines and not far from global extinction.

 

Disaster ahead for Sumatra's forests?

Alarm bells are ringing in Indonesia. 

An in-depth article just published by ALERT member Erik Meijaard in the Jakarta Globe suggests that the Leuser Ecosystem in northern Sumatra — the last place on Earth where tigers, orangutans, elephants, and rhinos still coexist — could be greatly imperiled.

Trouble ahead for tigers

Trouble ahead for tigers

The problem is the highly controversial “spatial plan” passed by the Aceh Provincial Government. 

The plan completely omits the Leuser Ecosystem — and according to Meijaard that’s because the Aceh government plans to log, clear, mine, and essentially destroy much of the Leuser environment.

That would be a tragedy wrapped in a disaster.  The IUCN lists the Leuser Ecosystem — a region of 2.26 million hectares rich in rainforests and peat-swamp forests — as one of the “World’s Most Irreplaceable Places”.

Beyond its unparalleled importance for biodiversity, the Leuser Ecosystem also provides vital environmental services for the people of Aceh — such as reducing flooding and droughts, protecting soils, and providing clean water for people, agriculture, and fisheries. 

The forests also store large quantities of carbon essential for limiting global warming.

As Meijaard argues, the natural services provided by the Leuser forests truly are vital. 

For instance, floods in December 2006 affected over 700 villages in Aceh, destroyed over 4400 homes, and killed 47 people.  Damage from the floods was estimated to total US$210 million. 

Imagine the toll from such an event if the Leuser forests — which help to limit destructive flooding — had been largely destroyed.

Meijaard and many others — including 141 scientific, environmental, and social-rights organizations — are urging Indonesia’s federal government to strike down the Aceh government’s ill-advised spatial plan, as the plan can't proceed without federal approval. 

Let’s hope common sense prevails in Indonesia, before one of Earth’s most unique and important ecosystems is lost forever.

Do the world a favor: Dob in an eco-sinner today

Want to do the world a favor?  The next time you see somebody harming wildlife or the environment, turn 'em in.

Dying for their skins...

Dying for their skins...

In late February we wrote about a new website called WildLeaks -- established especially for anonymously dobbing in environmental sinners.  Guess what?  It's working.

In just its first three months, WildLeaks has resulted in tip-offs for 24 major wildlife crimes, including leads on elephant and tiger poaching, and illegal fishing and forest destruction. 

The crimes that WildLeaks has recently unearthed include:

• elephant poaching in Africa and illegal ivory trading in Hong Kong

• the killing of perilously rare Sumatran tigers

• trafficking of live chimpanzees in Liberia

• illegal fishing in Alaska, with alleged links to the Mafia

• Illegal imports of African wildlife products into the US

• illegal logging in Mexico, Malawi, and Siberia

The designer of WildLeaks, Andrea Crosta, is a pro at this stuff.  An expert on elephant conservation, his past exploits include revealing how Somalian terrorists used ivory smuggling to fund their activities. 

WildLeaks takes the security of its informants seriously.  Every tip that WildLeaks receives is examined by a team of legal and security experts, who then liaise confidentially with relevant law-enforcement authorities.

Thanks to WildLeaks, those who profit handsomely from eco-crimes -- which total hundreds of billions of dollars annually --- will be spending a little more time glancing nervously over their own shoulders.