Web edition: August 2, 2007
Members of an established ecosystem develop a sense of balance, usually permitting at least limited biodiversity and a stable structure. When interlopers arrive that aren't responsive to the same environmental checks and balances, they can overrun the ecosystem, eliminating some members and quickly dominating others. Such bullying immigrants are known as invasive speciesand they can be newly introduced garden plants, fish, insects, trees, worms, even fungi. The U.S. Department of Agriculture offers one-stop shopping for news and impacts of such invasive species.