Wednesday, August 11, 2010

Invasion of the Invasive Species! - Local biodiversity is increasing

Here’s a fact that I suspect most people don’t know: Wherever we humans have gone in the past two centuries, we have increased local and regional biodiversity. Biodiversity, in this case, is defined as increasing species richness. Yet, “the popular view [is] that diversity is decreasing at local scales,” Brown University biologist Dov Sax and University of California, Santa Barbara biologist Steven Gaines report [PDF]. Ample scientific evidence shows that this popular view is wrong, however. For example, more than 4,000 plant species introduced into North America during the past 400 years grow naturally here and now constitute nearly 20 percent of the continent’s vascular plant biodiversity. The fear among opponents of "invasive species" is the aggressive outsiders will cause a holocaust among the native plants. That might initially seem reasonable because there are a few species, like kudzu, purple loosestrife, and water hyacinth, that grow with alarming speed wherever they show up. But that doesn't mean other species are in danger. “There is no evidence that even a single long term resident species has been driven to extinction, or even extirpated within a single U.S. state, because of competition from an introduced plant species,” Macalester College biologist Mark Davis notes [PDF]. Yet this spurious threat of extinction persists as one of the chief reasons given for trying to prevent the introduction of exotic species. Meanwhile, there are plenty more examples in which local and regional species richness has been increasing...more

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