Environmental Engineering Reference
In-Depth Information
Wilkinson is among the scientists who propose that the complex ad hoc interactions between native
species and aliens from many lands on Ascension are good evidence for an ecological theory that con-
tradicts mainstream ideas about coevolution. “Ecological fitting,” a term coined by US ecologist Daniel
Janzen, is used by scientists who hold that ecosystems are typically much more random. “The Green
Mountain system is a spectacular example of ecological fitting,” Wilkinson says. “It is a man-made sys-
tem that has produced a tropical forest without any coevolution between its constituent species.” Thomas
Jones of the US Department of Agriculture in Logan, Utah, agrees. On Ascension, he tells me, plants
gathered from across the world “self-organized by the mechanism of ecological fitting.”
This debate matters. It raises in practical form many of the questions I will explore in this topic.
What are ecosystems and how do they form and function? Are alien species “bad” and natives “good,”
or is this distinction false and scientifically unjustified? Could nature be far more resilient and far less
fragile than we imagine? Have we messed with the environment so much now that places like Green
Mountain, with their bizarre mixtures of natives and aliens, offer the best chance for nature's survival
in the twenty-first century and beyond? Is the success of aliens the most vivid expression of Darwin's
“survival of the fittest”? Should we—for the good of the natural world—learn to love the aliens?
Some regard such talk about alien species as nonsense. And it is true that not all alien species fit in
like respectable ecological citizens. Some create mayhem, especially within the simple ecosystems that
occupy many remote islands. Gough Island is another volcanic hulk far out in the South Atlantic. Like
Ascension twenty-five hundred miles to the north, Gough Island was discovered by Portuguese navig-
ators but only claimed much later by the British. They raised the Union Jack there in 1938 and named it
after Charles Gough, the first British sea captain to spot the island, two hundred years before. Gough has
no natural harbor. Climbing ashore is difficult. As a result, sailors have only ever set foot here about 250
times. That includes the seasonal change of its only current inhabitants, the South Africans who staff
the island's weather station. Yet seventy-one of the ninety-nine species recorded here were introduced
during those 250 visits. One of them is a big problem.
For as long as anyone knows, Gough Island has been dominated by millions of nesting seabirds.
When Britain nominated the island as a World Heritage Site back in 1995, the Royal Society for the Pro-
tection of Birds (RSPB) called it probably the world's most important seabird colony. Its ten million avi-
an inhabitants included 90 percent of the endangered Tristan albatrosses (
Diomedea dabbenena
) and the
entire world populations of both the ground-nesting Gough bunting and the flightless Gough moorhen.
The island is now also the only known breeding ground for endangered Atlantic petrels (
Pterodroma
incerta
). (The other colony, on Tristan da Cunha, was eaten by invading rats.)
There are no trees on Gough Island, and vegetation is mostly lichens and ferns. So to escape from
the wind and cold, the birds live in burrows. But this subterranean seabird megacity is under threat.
For there are new masters on Gough Island—the descendants of English house mice (
Mus musculus
)
that leaped ashore from Victorian whaling ships sometime in the nineteenth century. These are not nor-
mal mice, however. Not now. Over the decades of their windswept exile, they have doubled in size and
turned carnivorous. These mutant mice now typically grow to up to ten inches long and eat up to a fifth
of their body weight every day. With an estimated two million mice on just sixteen thousand acres, that
means they devour more than a ton of bird flesh every day from every acre of the island.
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