Why Robinson Crusoe island is at risk

Bursting with endemic flora and fauna, the Juan Fernández Archipelago is a hothouse of evolution. But alien species introduced by humans are now threatening this remote 'Galápagos of plants'. Science editor Steve Connor reports

It takes about two hours by light aircraft to fly to the remote Pacific islands of the Juan Fernández Archipelago, 414 miles off the coast of Chile. That's all it takes to destroy the 4 million-year isolation that has protected this oceanic jewel from biological destruction.

Most people who have heard of Juan Fernández know of its links with Daniel Defoe's classic desert-island tale of Robinson Crusoe (pictured, far right). Indeed, the biggest island in the archipelago was renamed Robinson Crusoe Island in 1966 in honour of a Scottish mariner called Alexander Selkirk who was self-marooned there in 1704 for four years and four months – an endurance test that is said to have inspired Defoe's imaginary character.

But the Juan Fernández Archipelago has a more important story to tell. It centres on a long history of geographical isolation that has made it one of the world's most exquisite hothouses of evolution. Its separation from the mainland has meant it has developed an endemic evolutionary signature of its own.

The islands are one of few places on earth that have never been colonised by humans until recently. Selkirk was not the first person to set eyes on the islands – that was the Spanish navigator Juan Fernández in 1574 – but his stay there marked the beginnings of a biological catastrophe that resonates on islands throughout the world. The Juan Fernández Archipelago epitomise what can happen to unique, endemic species when their remote territory is suddenly invaded by alien species introduced by man.

An endemic species is one that exists where it has evolved. On islands, they are often found nowhere else and are exquisitely vulnerable to invasive alien species. Juan Fernández is a microcosm of what's taking place in just about every remote, pristine island on earth where human encroachment has resulted in the introduction of foreign species. "One of the features of endemic species is that they are incredibly sensitive to change and the arrival of people usually springs dramatic change to islands, particularly when they bring new species with them," says Alan Saunders, a New Zealander with a vast experience of eradicating invasive species from islands. "At the end of the day we have two choices. Either we get rid of the invasives or we stand by and see extinctions taking place."

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The Juan Fernández Archipelago, which is administered as a "special territory" by Chile, consists of three principal islands. The second oldest, formed by an undersea volcanic eruption about 4 million years ago, is Robinson Crusoe Island. It was previously known as Isla Más a Tierra, meaning the "island closest to land", the name Selkirk knew it by.

Another island 121 miles due west of Robinson, and slightly larger with taller mountains and deeper ravines, is Alexandro Selkirk Island, although confusingly Selkirk himself never set foot on this island and couldn't even see it from his mountain-top lookout on Robinson Island. Alexandro Selkirk Island, in Selkirk's day, was called Isla Más Afuera, meaning the island further out to sea. The third island is Santa Clara which Selkirk could have seen but probably never visited. It is the smallest of the three and lies off the western tip of Robinson Island.

Daniel Defoe may have made this part of the world famous (although he never acknowledged in print that his fictional epic was inspired by Selkirk's adventures), but the real story of these dramatically beautiful islands is one of invasive alien species. These animals and plants have been introduced by humans, either deliberately or accidentally. They quickly establish themselves in a way that wipes out the endemics that arose there. They are different from the native, non-alien species that evolved somewhere else but have come to the islands naturally, living alongside the endemics. Scores of alien species have established themselves on the islands since Selkirk's day. The goats have been joined by rabbits and rats, feral cats and domestic cattle. Alien plants include blackberry brambles and Chilean myrtle berry shrubs – two of the most invasive and dangerous of the invading flora.

The endemic flora on Robinson and Selkirk islands are especially rich – and vulnerable – which is why botanists refer to the archipelago as "the Galápagos for plants". To date, scientists have identified 131 endemic plants on the islands, which means that nearly two thirds of the total number of native plant species found on the islands arose there – a floral endemism of 62 per cent. The islands have the highest density of endemic plants anywhere in the world.

But it is not just plants. The islands are home to three endemic avian species and four endemic subspecies – which means 45 per cent of Chile's entire quota of endemic birds can be found on these small Pacific outcrops of volcanic rock.

The level of species endemism in birds and other vertebrates alone, combined with the dire threats posed by the invasion of alien species, led to the Juan Fernández Archipelago being rated by the Durrell Wildlife Conservation Trust in Jersey as the most important eco-region in the world out of list of 100 threatened sites in dire need of preservation. "Juan Fernández has generated a large number of endemic species and the proportion of endemic species to total species richness is extremely high," says Stephan Funk, senior conservation biologist at the trust. "And endemic species on very small islands have nowhere else to go, which is why conservation efforts there are so important."

Of the 123 endemic plants that have been classified in a risk category, five have been declared "extinct", 72 are "endangered and rare", 21 are "endangered" and a further 21 have been classed as "vulnerable". Some 14 plant species have fewer than 10 individuals living in the wild, and a handful of plant species are represented by just one known individual growing in its natural habitat – the most precarious position for an endemic island plant.

The archipelago represents less than 1 per cent of Chilean national territory but accounts for 60 per cent of the country's extinct species, 55 per cent of the nation's "endangered" plants, and 59 per cent of those labelled "endangered and rare". It is easily the most critical region in Chile for plant conservation, and this is a country that is recognised as a global "hotspot" for plant biodiversity.

The deforestation of previous centuries has been largely stopped and the islands are now a protected national park as well as a biodiversity zone, but the problem of invasives is, if anything, getting worse. "The forests are fully protected, so there is no longer direct anthropogenic impact, but there are indirect effects of invasive species," says Peter Hodum of the University of Puget Sound near Seattle, who has studied the islands extensively. "We are no longer cutting forest but the fact that we've brought in species that have established themselves in remnant patches of intact forest is now the greatest threat to that habitat," he adds.

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Almost all the threats posed to the survival of the endemic animals and plants living in the Juan Fernández Archipelago stem from contact with Europeans. When Alexander Selkirk fell out with his captain and chose to abandon ship for the island of Mas á Tierra (Robinson Crusoe Island), he took a Bible, a pouch of tobacco, some clothing and bedding, a musket and powder, navigation instruments and a few tools, including a hatchet for chopping wood.

He thought he would only be there for just a few weeks before being rescued by a passing ship but the weeks turned to months and years. He survived by hunting the feral goats that had been introduced to the islands by previous mariners wanting to ensure a supply of fresh meat on the high seas. More than a century before Selkirk's adventure, the navigator Juan Fernández is said to have left just four goats on the smaller island of Más Afuera (Alexandro Selkirk Island). Now there are about 3,500 goats there.

Goats, which eat just about anything they can chew, were to be the start of a 300-year alien invasion. Domestic rabbits and cats soon escaped into the wild, the latter to deal with the rats and mice that jumped ship. And about 50 years ago, someone introduced a small South American predator called a coati – for no other reason than it would be of interest to people visiting Robinson Island. Like the cat and rat, the coati has made light work of ground-nesting birds.

The native and endemic birds, which include a seabird called the pink-footed shearwater (Puffinus creatopus) that digs underground burrows to lay its eggs, are no match for these introduced predators. The islands have no natural mammals apart from an endemic species of fur seal, and the native birds are quite unused to these intelligent, agile predators.

Like many endemic animals on remote islands they are incredibly naïve when it comes to invasive predators and do not display the usual flight behaviour seen in birds on the mainland. Ground-nesting birds in particular are also highly vulnerable to having their eggs stolen by four-legged predators, even those as small as rats and mice. Hodum says that even rabbits have been shown to disturb the breeding patterns of the pink-footed shearwater by invading its burrows.

As for the plant-eating invaders, their impact is just as devastating. Invasive herbivores can turn a rich landscape of temperate forests and fertile valleys into an overgrazed wasteland. Goats in particular are renown for nibbling the most-out-of-the-way shoots, preventing a mature forest from renewing itself with young saplings.

In many ways, invading plants can be even more pernicious than the invasive animals. The top three floral invaders are the elm-leaf blackberry (Rubus ulmifolius), the Chilean myrtle-berry bush or murtilla (Ugni molinae) and a South American shrub called the maqui (Aristotelia chilensis), which forms dense thickets where nothing but itself can grow. A common feature they possess is the ability to grow rapidly throughout the year. They quickly out-compete the native plants for light, nutrients and space and strangle endemics in their path.

But it's not just the endemic plants that are wiped out by these invading triffids. Take the case of the blackberry bramble, which was introduced on to Robinson Island as recently as the 1930s to serve as a boundary-forming hedging plant that would also provide fruit for jam. In the sub-tropical moist climate it grows vigorously throughout the frost-free seasons. In the space of three or four years it can overgrow a full-sized Luma tree (Myrceugenia fernándeziana), an endemic species on Robinson Island that is also the preferred nesting site for the island's iconic firecrown hummingbird (Sephanoides fernandensis), the only species of hummingbird in the world that is endemic to an oceanic island.

So an innocuous-looking plant brought to the island less than a century ago is helping push the world's only endemic oceanic hummingbird to the brink of extinction. Just 1,000 firecrown hummingbirds are believed to live on Robinson Island, compared with perhaps as many as 10,000 when Selkirk was stewing goat meat over a fire and dreaming of being rescued by a passing ship.

No-one knows how long the firecrown hummingbird has existed on Robinson Island – estimates range from 100,000 years to more than a million. It almost certainly evolved from a species found on the mainland of South America called the greenback hummingbird. A storm probably blew a few greenbacks onto Robinson Island many tens of thousand of years ago where they formed a breeding colony.

Once these marooned greenbacks had established themselves, a long period of isolation led to the evolution of a new species, with distinctively different coloration and behaviour to the greenback. (It is this process of speciation – the formation of new species – that Charles Darwin discovered after he had visited the Galápagos islands to the north of Juan Fernández.)

The firecrown's unique traits include the widest differences in physical appearance between the two sexes of any hummingbird – so different are the males and females compared to other hummingbirds they were originally thought to be two species. Firecrowns also exhibit the charming habit of saving valuable energy by sometimes grasping on to the underside of a nectar-filled flower with their feet to take a rest from hovering.

Like many species that have evolved on islands, the firecrown exhibits a remarkable tameness. Within hours of landing on Robinson, I encountered a family of firecrowns feeding on the dangling orange flowers of an abutilon bush, a non-native but non-invasive species. To my surprise I could almost reach out to grasp these little birds without them showing any signs of fear. As one might expect, such naïvety is lethal in the presence of the many feral cats living on Robinson. As Peter Hodum says: "For cats, it's like a walk-in supermarket you don't have to pay for."

But even if a young firecrown survives the attentions of the local cats long enough to breed, its eggs can still be eaten by the island's band of climbing black rats (Rattus rattus). That is if they can still find a nesting site in any of the tall Luma trees that have not yet been strangled by blackberry brambles.

As iconic as the firecrown is, however, it is not the most endangered bird in the Juan Fernández Archipelago. That is a small songbird called the Rayadito de Masafuera (Aphrastura masafuerae) that lives on the more distant Selkirk Island, which was formed about a million years ago during an undersea volcanic eruption, making it about 3 million years younger than Robinson Island.

Ingo Hahn, a young ornithologist from Muenster University in Germany, probably knows more than anyone about the mysterious rayadito, which lives within the steep and highly-inaccessible ravines on Selkirk, an island with an exceptionally difficult terrain. Hahm spends up to 10 weeks at a time studying the bird on his own in the hope of working out how it lives so that scientists can come up with some kind of meaningful strategy for saving it from extinction.

By mapping the territorial boundaries between competing rayaditos, Hahm has come up with an estimate of the bird's breeding population. He reckons there are just 140 individual rayaditos still living on the island – the only place they are found. "It is the rarest endemic animal species of Chile," Hahm says.

And it's getting rarer. The island's goats are eating through the rayadito's habitat of endemic plants, and rats take any eggs they can find. This is why the rayadito is one of the most endangered birds in the world.

But as rare as the rayadito is, its predicament is not as precarious as some of the archipelago's endemic plants. One species, called Chenopodium sanctae-clarae, is represented in the wild by just one community of individuals living on a single rock on Santa Clara island, which thankfully has had its goats eradicated. Several other plants exist only as a single individual in the wild. One such species is Dendroseris gigantea, with a final representative in nature that is a lone plant on Selkirk Island, although it is now being propagated artificially on Robinson Island.

Should these single individuals die out in the wild without any propagation in captivity, then so does the species – and another extinction occurs. This happened a few years ago to the last living male plant of a species called Robinsonia berteroi, type of groundsel, which was chewed to death by rats. No one had thought of protecting it.

One of the most unusual gems on Robinson is a flowering plant belonging to a plant family called the lactoridaceae. DNA studies and discoveries of fossilised pollen in other parts of the world indicate that this family may be something like 100 million years old, yet the only living specimens exist on Juan Fernández, which is no older than 4 million years old. It has been studied by Tod Stuessy, a botanist and Juan Fernández specialist at the University of Vienna.

"The lactoridaceae in the archipelago are the only family of flowing plants restricted to an oceanic island. They represent a remnant population of something that probably went extinct everywhere else millions of years ago," Dr Stuessy says. "It's a mystery how they got there."

It's rather like finding a family of dinosaurs living on the Isle of Wight.

The importance of the archipelago in terms of its endemic flora cannot be underestimated. It is not so much the total number of endemic flora that can be found in the "Galápagos for plants", it is their sheer density – something I experienced for myself.

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Walking half the length of Robinson Island, a distance of some 10 miles, with botanist Philippe Danton of the National Museum of Natural History in Paris, is an exhilarating if exhausting experience. The footpath from the western point of the island climbs slowly to the tall, volcanic peaks that bisect one half of Robinson from the other. Selkirk had his lookout at this summit. Standing on Selkirk's rock, it is possible to scan both the east and west horizons at once. It became a daily ritual for Selkirk.

As we moved from the lower grassy slopes to the forested peaks with their lush tree ferns and tall Lumas, the trilling sounds of the firecrown hummingbird were punctuated by Danton's frequent calls of "endémique!" as he spied yet another Robinsonian rarity. In the space of several hours, I lost count of how may "endémiques" he had documented.

Danton has witnessed many changes to Robinson in the 12 years he has spent surveying the island's flora. "The firecrown hummingbird is a bird from the forest and I had a chance when I started working here to see some parts of the pristine forest," he says. "Today, there is not one part of the forest where you cannot find an invasive species – they are everywhere, in every part of the forest. It would be difficult for Selkirk to recognise the forest now."

Of all the invasive species to have arrived on the islands of Juan Fernández , humans must rate as the most destructive, even without their role as a vector for alien species. Since Juan Fernández first charted the position of the archipelago in 1574, humans have transformed the landscape, which had until then escaped human colonisation, either by the Polynesian seafarers to the west, who stopped at Easter Island, or the South American natives to the east.

When European mariners arrived, they quickly exploited the forests for wood. Robinson has also been a penal colony and the site of a Spanish castle. In 1853, a permanent colony of settlers from the Chilean mainland was established and cattle were introduced to graze the lower grassy slopes that had been cleared of trees.

Today, Robinson Island has a permanent population of about 750 inhabitants living in the tiny village of San Juan Bautista overlooking the same Cumberland Bay where Alexander Selkirk's ship landed in 1704. The population has risen by 150 in just two years, which is on top of the 2,500 tourists who visit the island each year.

Ivan Leiva Silva, who has been director of the Juan Fernández National Park for 15 years, says that 75 per cent of the land on Robinson Island has suffered erosion though deforestation, fires and overgrazing by livestock. He says 40 per cent of this erosion is irreversible, and of the 1,800 hectares of forests on the island, just 250 hectares are still in the same pristine state they were in when Selkirk chopped wood for his fire.

But Leiva Silva still has hope for what remains of the archipelago's endemic wildlife. He has witnessed a change in the mood of the Robinson islanders, especially the younger generation, who have come to realise that a sustainable future for them means looking after what is left of the archipelago.

There are now delicate discussions taking place between the Chilean government, the scientists and the islanders on the eradication of the invasive species. The locals support the removal of rats and feral cats, at least on Selkirk Island, but there are reservations about removing the goats, which they see as part of their culture. On Robinson, islanders still keep pet cats, but they are neutered and registered, each with their own identification collar.

The Chilean government's National Commission for the Environment (Conama) is supporting a conservation action plan for the Juan Fernández islands and, ultimately, it will be for Chile's government to decide on what eradication measures will be introduced, which can be legally enforced in what is, after all, a national park.

But time is running out. Philippe Danton wonders whether it is too late. "I am rather pessimistic because urgent action is needed to save the extraordinary biodiversity that is here. It's a very difficult battle," Danton says.

"We are going to learn a lot from this experience. This is an island, which is a small world surrounded by water. I live in a bigger world, and the planet is also like an island. The planet is in a bad state so everything we learn from studying this smaller world would be very useful for the future," he says.

"Since a child, I have been told that mankind is the only intelligent species. Now I would like us to prove that."

The real Crusoe: Alexander Selkirk

I am monarch of all I survey,

My right there is none to dispute;

From the centre all round to the sea,

I am lord of the fowl and the brute.

William Cowper's poem, The Solitude of Alexander Selkirk, immortalised a man whose experiences were said to have also inspired Daniel Defoe's Robinson Crusoe. The seventh son of a cobbler, William Selkirk was born in 1676 in Lower Largo, Fife. He ran away to sea to avoid an appointment with the local courts over a fracas with his brother and ended up on the 16-gun privateer the Cinque Ports with a royal licence to plunder Spanish ships.

He fell out with the ship's captain, convinced the vessel was unseaworthy, and asked to put ashore on the uninhabited island of Más a Tierra. But almost as soon as the ship weighed anchor in September 1704, Selkirk had second thoughts and pleaded to be let back aboard – a request the captain refused.

Selkirk took with him a few tools, a cooking pot, a musket and powder, tobacco and a Bible. He ended up staying on the island for four years and four months. He lived on cabbages and turnips and hunted the island's feral goats, which he caught by running them down on foot.

When his clothes wore out, he sewed goat-skin trousers, jacket and hat. He spent much of his time reading his Bible or waiting at his lookout post on a mountain pass, where he would scan both east and west horizons for passing ships.

Once, a Spanish ship docked in the bay and he had to run away and hide in a tree, fearing the Spanish would make him their slave. Eventually, in 1709, he was rescued by a British ship. The captain, Woodes Rogers, remarked that Selkirk could barely speak and looked wilder than the island's goats.

Island endemism: Darwin's discovery

One of Charles Darwin's great achievements was to provide an explanation for how new species arise through natural selection. He realised islands play a key role because they allow a few stranded members of a species to become geographically and reproductively isolated from their tribe. The isolation, over many generations, eventually leads to a physical and genetic divergence, and hence the evolution of a new species that becomes endemic to that island. The islands of Juan Fernández are far enough away from the mainland for island endemism to have occurred many times, but not too far as to never receive occasional visitors from the mainland.