Out of Eden: An Odyssey of Ecological Invasion by Alan Burdick. Farrar, Straus and Giroux, $25, 325 pages.

The Atlanta Journal-Constitution

July 10, 2005

Pesky truth on invasives

By PHILLIP MANNING


They usually come by plane or boat. Most of the time we don't notice them, but occasionally, they cause serious trouble. They are invasive animals and plants --- organisms that behave well at home but can be disruptive when dumped into a new neighborhood.

Invasives are not the villains; we are. We transport species around the world, deliberately and accidentally. We brought fire ants from South America, the chestnut blight from Japan and kudzu from Asia. Scientists have begun to study invasives intensively, and their findings are shaking the foundations of ecology.

In "Out of Eden," Alan Burdick, a senior editor for Discover magazine, explores the new science of invasion biology and travels the world with these scientists, investigating lava tubes in Hawaii, sampling the water in San Francisco Bay and searching for snakes in Guam.

Invasives are everywhere, Burdick tells us. San Francisco Bay, for example, has more than 200 introduced species in its waters. Many of the new species arrived when ships from other countries dumped ballast water taken on at their home ports into the bay.

Such human-assisted migrations of organisms are not all bad. They add to the local biodiversity; more species live in San Francisco Bay now than lived there before invasions. And most introduced species have little impact on native plants and animals. Some, however, cause havoc.

One particularly bad actor is the brown tree snake. Introduced into Guam, most likely as a stowaway from New Guinea on military aircraft during World War II, the bird-eating snake has almost completely devoured the island's avian life.

Another problem species, the zebra mussel, arrived in the Great Lakes in the 1980s, almost certainly in ballast water. Since then, its exploding populations have decimated native clam species and shut down power plants and towns by clogging their water-intake pipes.

Altogether, Burdick writes, the federal government estimates that "between 1906 and 1991, seventy-nine nonindigenous species --- including, most notably, the European gypsy moth and the Mediterranean fruit fly --- had cost the nation ninety-seven billion dollars."

The problem of invasives is real, all right. What to do about them is the challenge facing invasion biologists.

Charles Elton, a founder of ecology and an early student of invasions, argued in his 1926 book "Animal Ecology" that groups of plants and animals are not "mere assemblages" but are "closely knit communities or societies." Elton went on to say, "The balance of relatively simple communities of plants and animals is more easily upset than richer ones." Greater diversity, Elton said, conveys "biotic resistance" that helps a natural community repel invaders. This hypothesis has become a canon of ecological science.

Recent findings contradict this. They indicate that invasives take hold as readily in species-rich natural communities as in depleted ones. The common English sparrow has been as successful an invader of species-rich America as the brown tree snake has been in Guam, which has far fewer species. But even the English sparrow had to be repeatedly introduced before it caught on.

Burdick sums up the messy situation: "Invasion success is nothing more complicated than . . . the frequency and persistence of the introduction."

Can we learn how to move around the planet without dragging noxious species with us? A new law mandates that ships entering the Great Lakes must replace the ballast water taken on at their home ports with sea water to eliminate freshwater hitchhikers. Though it is too late to stop zebra mussels, the new law is a start. But no law will ever be foolproof. As Burdick puts it, "Wherever humans go, it seems, we go with company."
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