We are not 'just speeding up' natural processes. We are swamping ecosystems with an unprecedented scale and variety of newcomers. The rate of introduction of new species is thousands of times faster at our hand. Timing and scale are fundamental in biology: change them and you change a phenomenon profoundly. Everyone knows that poison is in the dose. Seventy-five heartbeats per minute are healthy; 150 are not. A hurricane is not just early delivery on all the month's breezes.

Further, the crowd of new arrivals we are loosing on ecosystems includes not just neighbors that might have wandered in anyway but also plants and animals from other continents that we have helped across previously insurmountable oceanic barriers. No natural force would have put the loblolly pines of the American Southeast in the unlikely embrace of Japanese honeysuckles or rafted a population of pigs to the Galapagos or allowed an Asian tiger mosquito to meet up with an African encephalitis virus in the tunnels of New York.

There are limits to which and how many species can pack together into the world's shrinking supply of natural habitat, and limits to how fast ecosystems can adjust to new faces without jettisoning current occupants. Every time a wave of cosmopolitan invaders eliminates a rare, uniquely local species, the diversity of life on the earth is diminished. Packing the maximal number of creatures into one place is not the way to preserve biodiversity. If it were, a crowded zoo would suffice. When it comes to the diversity of life, we can have it all, but we cannot have all of it everywhere.…

No one advocates an attempt to unscramble the world's biota and return it to some historical state, even if that were possible.  But not everything that can invade has invaded, and damage from current invaders can be lessened or eliminated. Our ultimate goal must be not to vilify or destroy an invader or set of invaders but to preserve or restore something we value: native biodiversity and the wild places and systems where it can thrive, the look of a landscape, a sense of place, the functioning of an ecosystem, the economic productivity of our working lands and waters, the health of people, animals and plants."

From the introduction to "A Plague of Rats and Rubbervines: The Growing Threat of Species Invasions," by Yvonne Baskin, June 2002, Island Press/Shearwater Books