Quantifying Threats to Imperiled Species in the United States.

Assessing the relative importance of habitat destruction, alien species, pollution, overexploitation, and disease:

Biologists are nearly unanimous in their belief that humanity is in the process of extirpating a significant portion of the earth’s species. The ways in which we are doing so reflect the magnitude and scale of human enterprise. Everything from highway construction to cattle ranching to leaky bait buckets has been implicated in the demise or endangerment of particular species. According to Wilson (1992), most of these activities fall into four major categories, which he terms “the mindless horsemen of the environmental apocalypse”: overexploitation, habitat destruction, the introduction of non-native (alien) species, and the spread of diseases carried by alien species. To these categories may be added a fifth, pollution, although it can also be considered a form of habitat destruction.