Humans are highly dependent on nature's biodiversity. This biodiversity, however, is threatened by accelerating extinction rates that are approaching past levels of mass extinction. Human activities are largely responsible for this trend, and while there has been some success in preserving select species, the scale of impending extinction will require the conservation of existing ecosystems if biodiversity is to be preserved. Fortunately, the relative geographic concentration of most biodiversity makes such efforts possible and economically feasible. The last 400 million years of Earth's biological history have been marked by five major extinction periods, in which existing life was largely replaced by new forms. The most recent of these occurred approximately 65 million years ago, marking the end of the Mesozoic era. Now, the evidence indicates that another of these catastrophic periods is beginning, with one key difference; it will be carried forward by humans. For every 150,000 inhabitants of human existence the rate of extinction has increased by a factor of 100, and perhaps even by a factor of 100....