Transportation of species to areas outside their native ranges has been
a feature of human culture for millennia. During this time such
activities have largely been viewed as beneficial or inconsequential.
However, it has become increasingly clear that human-caused
introductions of alien biota are an ecological disruption whose
consequences rival those of better-known insults like chemical
pollution, habitat loss, and climate change. Indeed, the irreversible
nature of most alien-species int- ductions makes them less prone to
correction than many other ecological problems. Current reshuffling of
species ranges is so great that the present era has been referred to by
some as the "Homogocene" in an effort to reflect the unique mag- tude of
the changes being made. These alien interlopers often cause considerable
ecological and economic d- age where introduced. Species extinctions,
food-web disruptions, community alte- tions, ecosystem conversion,
changes in nutrient cycling, fisheries collapse, watershed degradation,
agricultural loss, building damage, and disease epidemics are among the
destructive - and frequently unpredictable - ecological and economic
effects that invasive alien species can inflict. The magnitude of these
damages c- tinues to grow, with virtually all environments heavily used
by humans now do- nated by alien species and many "natural" areas
becoming increasingly prone to alien invasion as well. Attention to this
problem has increased in the past decade or so, and efforts to prevent
or limit further harm are gaining wider scientific and political
acceptance.