Posted 9:30 PM by Luigi
Ecological invasions

Out of Eden: An Odyssey of Ecological Invasion by Alan Burdick
Farrar, Straus and Giroux, 2005

A review by Laurence A. Marschall

STANDING IN A LUSH FOREST on the Pacific island of Guam, science writer Alan Burdick is haunted by an eerie silence. Not a single warble, tweet, or chirp can be heard—nothing but the faint buzz of insects, the passing hum of a distant airplane, and the hushed rustle of the wind.

Guam’s songbirds have all vanished, victims of the brown tree snake. An exotic predator native to Australia, New Guinea, and nearby islands in the eastern Pacific, the snake arrived unannounced in a military vessel sometime around 1949. Such birds as the bridled white-eye, the Guam flycatcher, and the Mariana fruit dove, once widespread on the island, now exist only as stuffed museum specimens or illustrations in birders’ guidebooks. Even some nonavian natives—the Mariana fruit bat, for instance—are rapidly disappearing under the attack of the resourceful reptile.

Guam may be an extreme case of a habitat devastated by a hungry immigrant. But it is not uniquely vulnerable just because it is a small, isolated island. In 1988 the zebra mussel, once confined to the lakes and rivers of Europe, hitched a ride to Lake Erie, presumably in the ballast tanks of a visiting freighter. Today zebra mussels flourish throughout the Great Lakes, and can be found in the Mississippi River and its tributaries, as far south as New Orleans. Native clam populations in the Great Lakes have been decimated, and other species that compete for food with the mussels are in sharp decline. Accumulations of zebra mussels clog municipal water systems, and have even been known to sink navigational buoys by their combined weight alone.

Burdick points out that nowhere on the planet does nature survive in an Edenic state, unaffected by nonnative invasions: American gray squirrels now live in the British Isles; Asian longhorned beetles, which infested New York City maple trees in Brooklyn in the mid-1990s, now threaten the trees of Central Park; visitors to Hawai’i who marvel at the variety of flowers in the tropical island paradise are likely to be admiring plants that are visitors there, too: most species of lowland flora in Hawai’i were introduced by settlers in the past few centuries.

Burdick implies that even the “pure” Edenic state is a human invention. Would we know one if we saw it? And if we did, would returning to it be environmentally sound? Invasion is a process inherent in global ecology. Siberian woolly mammoths made their way over the Bering land bridge to the New World long before mercantile ships made the journey. Insects and worms hitchhike the ocean on bits of flotsam, coming ashore wherever the winds and currents take them. The capacity of plant and animal life to spread over the globe is what made it possible for newly emerging landmasses to develop their own indigenous forms of flora and fauna in the first place. Without invasive species, volcanic islands would have remained as barren as they were when they emerged, millions of years ago, from the floor of the sea.

What’s more, people are hardly latecomers to this process. The Polynesian settlers of Hawai’i brought the first pigs to the islands; centuries later, British soldiers carried the first cattle there. Settlers in the New World were diligent both in exporting American indigenous plants back across the Atlantic, and in bringing the plants and animals of their European homelands to American soil. Modern air and ocean transportation has only accelerated the process.

Burdick began this book, I sense, in an attempt to uncover nature at its “purest.” He found that it was difficult, perhaps impossible, to define ecological purity at all. In most cases, the leakage of species from one habitat to another has been going on for so long that ecologists have no way of knowing what an “indigenous” ecosystem might look like. Moreover, whether an invasion is benign or clearly devastating, such as that of Guam’s brown tree snake, it may be impossible to reverse. One lesson of Burdick’s odyssey is that there is no such thing as a “state” of nature—only a continuous dynamism that challenges our ability to understand, preserve, and manage.