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Eco-Defense against Invasions

2005; Public Library of Science; Volume: 3; Issue: 12 Linguagem: Inglês

10.1371/journal.pbio.0030429

1545-7885

Virginia Gewin,

Insect and Arachnid Ecology and Behavior

O nce thought only science fi ction, alien invasions are one of today's major scientifi c challenges.The "aliens" in question are nonnative, or exotic, species capable of outcompeting natives and, ultimately, taking over the ecosystems to which they are introduced (Figure 1).Invasive alien species are a worldwide problem, now found in every ecosystem on Earth.Staving off the further advance of invasions-identifi ed by the Millennium Ecosystem Assessment (http:⁄⁄www.millenniumassessment.org/en/index.aspx),a United Nations-backed audit of ecosystem health, as one of the most important drivers of ecosystem change-is a key environmental priority.Complicating matters, not all exotic species are invasive, or likely to cause harm to ecosystems or human health.But when introduced species exploit a specifi c species trait or fi ll a vacant niche in an ecosystem in order to invade, they cross the line from exotic to weed or pest.For example, European cheat grass (Bromus tectorum), accidentally introduced into western United States in contaminated seed, grows in the winter.Perennial grasses native to the west die off in the winter, giving cheatgrass the advantage of spreading healthy seed early in the growing season.Subsequently, Cheatgrass has altered the normal functioning of western ecosystems.Fires, once common in the region only every 60-100 years, now burn every three to four years.Animal introductions can lead to species extinctions if they upset existing predator-prey relationships.When the poisonous brown tree snake (Boiga irregularis) was accidentally introduced to the originally snake-free island of Guam in the Pacifi c Ocean, as a cargo ship stowaway in 1952, it ultimately caused the demise of twelve native bird species.The ecosystem's unfi lled predatory niche offered the brown tree snake the perfect opportunity to invade.Over 50 years later, the brown tree snake not only poses a human health risk (it's poisonous), but it also routinely disrupts power by crawling on electrical lines-both of which necessitate costly ongoing management.The majority of introductions occur accidentally, as a result of human movement.From the exotic ornamental garden species to the pest control agent to the hitchhiker, these introduced nonnative species can be arbiters of economic and ecological mayhem.Governments so far have been fi ghting a costly, losing battle against invasions.The containment, removal, and control of invasive species costs $137 billion per year in the US alone, according to David Pimentel, economist at Cornell University in Ithaca, New York.Conservationists say reliable reconnaissance-identifying the potential invasives early enough to implement costeffective eradication efforts-is the best defense against invasions.But that's easier said than done.With a notorious lack of funding for this growing environmental threat, conservation managers, not surprisingly, want to focus efforts on those areas that appear most vulnerable.But even identifying those areas has proven elusive.While pragmatic, predictive approaches for identifying likely invasions must be developed, the underpinning ecological mechanisms of Eco-Defense against Invasions