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On a remote island, lessons in how ecosystems function

By Fred Pearce - posted Tuesday, 17 September 2013


Likewise, the profusion of Ascension land crabs - the island's largest native land animals - that now feast on the fruits of alien trees like the guava. The only researcher to have studied the land crabs in recent times, Richard Hartnoll of the University of Liverpool, says that the invasive vegetation "increases the area of shade and shelter for crabs, and also provides a large resource of food" - perhaps replacing their former scavenging on seabird colonies.

You might think that this snugness would be of huge ecological interest? Yet, until now, visiting scientists have ignored it, says Stroud. Most researchers who make the long journey - the only practical way in is aboard a British military flight - have concentrated on the island's charismatic populations of seabirds, green turtles, and the handful of endangered ferns.

This blindness in research extends to conservation, says Wilkinson. The British government'senvironmental policy for the island is the "control and eradication of invasive species" in order to "ensure the protection and restoration of key habitats." (A major exercise to eradicate feral cats has been implemented under this policy.) But the policy has nothing to say about the protection of - or even ecological research into - the extraordinary novel ecosystem in their midst on which the indigenous species often depend.

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That is a shame. For, according to an increasing number of ecologists, the unique ecosystem on Green Mountain may hold important lessons about how ecosystems around the world function. In the growing scientific literature over the past decade about "novel" ecosystems, in which human agency or interference is a central factor in their makeup, Green Mountain is one of the most cited examples. More than that, the mountain's ecosystem calls into question a series of widely held assumptions about how complex, biodiverse ecosystems evolve - or indeed whether they evolve at all.

According to mainstream ecological theory, this cloud forest really should not exist. Certainly it should not thrive. Complex forests ecosystems are believed to take millions of years to develop, as each species evolves to fill its own niche in the system, creating a perfected "climax" ecosystem. But Green Mountain doesn't fit that paradigm. It just seemed to happen according to the chance introductions of British sailors.

As Stroud and Catling wrote, species on Green Mountain "have bucked the standard theory that complexity emerges only through co-evolution." On Ascension, plants gathered from across the world "self-organized by the mechanism of ecological fitting," says Thomas Jones of the U.S. Department of Agriculture in Logan, Utah.

The implications are important. Wilkinson is among the scientists who have proposed that the Green Mountain forest is good evidence for an alternative ecological theory - ecological fitting. A term coined by University of Pennsylvania ecologist Daniel Janzen, it holds that ecosystems are typically much more random. Stuff happens.

Not everyone agrees. Alan Gray, an ecologist at the University of Edinburgh in Scotland, suggests that some species that washed up on Ascension may have known each other before. "There would appear to be a high likelihood of importing already established coevolutionary relationships," such as moths and other invertebrates arriving with the trees in which they have evolved to lay their eggs, he says. According to Stroud, there has been no systematic study of invertebrates to unravel this conundrum.

Nonetheless, Wilkinson argues that the accidental cloud forest suggests strongly that even highly biodiverse ecosystems may often be accidental, temporary, and versatile.

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Whatever the truth, the stakes are high for ecologists. But while the ideas about ecological fitting go against the grain of mainstream thinking among environmentalists, they are not out of line with the teachings of Charles Darwin. Some see co-evolution and the creation of perfected ecosystems of native species as the ecological flowering of Darwin's thinking on evolution. But the evolutionary biologist Stephen Jay Gould has been among those who disagree strongly.

In an essay published in 1998, he attacked the "romanticism" of ecologists who sought to protect native plants against invasive species. He said their idea that Darwinian evolution created collections of species that were perfectly evolved to work together, like cogs in a machine, was false. "The Darwinian mechanism includes no concept of general progress or of optimization," Gould wrote. In fact, Darwin never said it did. Most of the time, species simply fitted in as best they could. "Survival of the fittest" was just that.

Whatever the theoretical implications of the forest on Green Mountain, there are practical implications for conservationists, too. Harvard University ecologist E. O. Wilson has said that the 21st century will be the century of ecological restoration. And Green Mountain suggests that restoration could be much easier than many believe. Ecologists may not have to painstakingly reassemble the complex ecosystems that have been lost. They often may be able to let nature take its course.

As Wilkinson put it: "Is it possible... to suggest, for example, that large deforested areas of Amazonia could be returned to functioning forest on a 100-year time-scale?" And maybe not just former rainforests. If a forest can form so quickly and successfully on a volcano in the middle of the Atlantic, they why not in other unlikely places?

As Catling and Stroud note, "Green Mountain might help inform strategies to green some deserts or other barren locations in the world."

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This article was first published on Yale Environment 360.



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About the Author

Fred Pearce is a freelance author and journalist based in the UK. He is environment consultant for New Scientist magazine and author of the recent books When The Rivers Run Dry and With Speed and Violence. His latest book is Confessions of an Eco-Sinner: Tracking Down the Sources of My Stuff (Beacon Press, 2008). Pearce has also written for Yale e360 on world population trends and green innovation in China.

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