The biodiversity hotspots are regions known to hold especially high numbers of species found nowhere else, yet their remaining habitat combined covers a little more than two percent of Earth's land surface. According to the criteria developed by Myers et al. (2000), a hotspot must meet two thresholds in order to qualify: 1) it must have at least 1500 endemic, native vascular plant species, and 2) it must have already lost at least 70% of its primary, native vegetation. In the updated analysis, Mittermeier et al. (2004) recognize 34 hotspots which together hold 50% of the world's plant species and 42% of all terrestrial vertebrates as endemics. As evidence of their urgency for global conservation, hotspots also hold exceptionally high numbers of threatened vertebrates, including 50% of threatened mammals, 73% of threatened birds and 79% of threatened amphibians as endemics. There are an estimated two billion people living in the hotspots, with 300 million people within less than 10 km of existing protected areas.