"The invaders are legion: escaped pets; sports fish and garden plants run amok; bugs that came hidden in the foliage of introduced garden plants; pests that were introduced to control other pests, with greater or, usually, lesser success... the invaders are from anywhere, going everywhere."
The brown tree snake dominates the cover of Alan Burdick's Out of Eden: An Odyssey of Ecological Invasion, sprawling across the front, its tail wrapped around the back. That's fair enough. The story of the snake's conquest of Guam takes up the first fifth of the book, making it the poster child for invasives (this book has been one of my main sources for this month's Mariana theme). Eventually leaving Guam, the author takes the reader island hopping around the world, from Tasmania to Hawaii to the inverse-of-an-island, the Great Lakes. All the while, he tracks the invasive species which are wreaking ecological havoc, as well as encountering the biologists who are trying to control them.
Out of Eden is about invasive species, but it's also about the people who unwittingly (and sometimes deliberately) spread them around the world. Humans are the ultimate dispersal system, and Burdick examines in detail how we move animals around the world. The brown tree snake hitches rides on planes. Barnacles, green crabs, and other marine invaders travel in ballast water. An experiment to recreate how canoeists populated the islands of the South Pacific also proved to be an experiment in invasion biology, as the canoes were quickly filled with stowaways (including a particularly obnoxious gnat species). Burdick even tours a NASA facility to consider how humans could potentially transfer life around the cosmos... or bring an alien invasive back to earth.
The book raises interesting questions about what it means to be an invasive. Pigs have run feral on the Hawaiian islands for over a thousand years, and have an integral role in Hawaiian culture. Their impact on native ecosystems has been very negative, but native Hawaiians scoff at efforts to eradicate them. They belong here, they say - might as well try to eradicate us. How long does it take for an invasive to become a native? Similarly, what would happen if the brown tree snake had reached Guam not in an airplane wheel well, but on a floating raft of vegetation, reaching the island without human assistance. Would that invasion have been natural? In that case, should we have stood by as the snake ate its way through the island's avifauna?
Zoos receive scant notice in the book. Burdick mentions that some Guam birds - the Guam rail and the Micronesian kingfisher - were saved in zoos. He also mentions that zoos will sometimes accept confiscated animals intercepted at customs. One aspect which is not considered is zoos as a source of invasive species through escapes. It's an unlikely occurrence, but one that many government agencies take seriously, hence the stringent regulations on which zoos are allowed to house some potentially invasive species.
Most importantly, Out of Eden challenges the role of humans in a natural system. Are we - and our brains, our behavior, our traveling - part of nature, and the consequences of our actions part of that natural system? Or do we have an obligation to correct our introductions, accidental or otherwise?
Out of Eden: An Odyssey of Ecological Invasion at Amazon.com