A few reasonable questions a person might have about Out of Eden: An Odyssey of Ecological Invasion

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What is your book about?

Foremost, it's about the conservation issues posed by alien species: how the increasing movement of species globally threatens the many, small pockets of biological diversity around the world, and diminishes the ecological uniqueness of any given place. One scientist I spoke to referred to it as the "McDonaldsization" of nature.

At another level, the book is a sort of Richard Attenborough documentary about natural science: what ecologists are learning about how nature works by studying alien species, and the philosophical challenges involved in doing fieldwork. One scientist who read a final draft of the book said I'd manage to capture the "bloodiness" of science — by which he meant its inner workings, the amount of human effort and interpretation that goes into turning raw data into stable facts. The sight of that blood unnerved him, but I took it as a compliment.

The book is also very much a travel story — an outward one, through a physical environment of weird, on-the-move creatures and changing landscapes, but also an inward one, through metaphysical, even spiritual questions about what we want from nature and our place on Earth. And it's a human story. In one way or another, all the characters in the book are asking themselves what "home" means: where and how to create one for themselves, and how various biological invaders affect that search.

I tried to weave all these themes into a personal narrative. The result, I hope, is an engaging read.

Are you for alien species, or against them?

Well, I'm for them, insofar as I think we can learn a lot from them. By studying what happens when new species enter an environment, scientists have reconsidered many basic assumptions about how ecosystems allegedly work. It turns out that nature is a lot more resilient than we thought, and the ecological rules at play are much less orderly than expected. These insights in turn present the rest of us with some very challenging questions about what we expect and require from nature and how best to achieve it.

That said, alien species do throw into relief the plight of the world's native species — the rare flower pollinated only by one kind of long-beaked bird, or the albino cricket found only in a lava-carved cave in Hawaii. Those organisms represent a timescale — natural selection played out over thousands of years — that vastly exceeds our own individual time on Earth, and that's a timescale worth preserving, I think, if for no other reason than the aesthetics of it: the novelty and strange beauty of these organisms; the fact that they came into being with no help from us, though they now require our artfulness to survive; and the fact that they help give a unique texture to every region of the world. They're like priceless art, and I'm a fan of the arts.

What is the Godzilla of introduced species? What is the organism we ought to know more about?

The brown tree snake, originally from Australia, poses a real threat. Since it first arrived on Guam some fifty years ago, it has managed to eat virtually every bird on the island, and has driven two bird species utterly extinct from Earth. Lately it has begun appearing in Hawaii, which is home to 40 percent of the nation's endangered birds. If it becomes established, it could deal a serious blow to the native birds — which have already been hit hard by introduced avian malaria. Unfortunately, the snake is so good at staying hidden that decades could pass before scientists know for sure that it's living in Hawaii — by which point it will be too late to stop it. The Florida Everglades may have a similar problem now with Asian pythons and boa constrictors; so many have been imported and set free in South Florida that they now live and reproduce outdoors there. A few years ago someone caught a 22-foot python that had been living under a home in suburban Miami.

That said, some of the worst aliens are quite familiar to us. Pet housecats and feral cats, which are originally native to the Near East and Africa, already do tremendous damage to the nation's bird population, but we don't usually consider them an "alien species" problem. The grazing and trampling of livestock, which are likewise introduced species, are a bigger threat to native plants globally than the more exotic alien species one might conjure up. By the same measure, much of what counts as alien-species damage — by introduced insects and pathogens, for instance — is done to our lawns, gardens, and crops, which are themselves made up almost entirely of alien species. We've developed such close, dependent relationships with so many introduced species that we sometimes forget what we mean by "alien."

Personally, lately, my biggest alien-species worry is the virus responsible for the avian flu in Asia. If it manages to mutate into a form that can spread directly between humans, instead of simply between poultry and humans, it could quickly jump across borders, with frightening consequences.

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