Since most species are unknown and unmonitored, the relatively well-studied vertebrates offer one of the best windows on why and how species are declining. The leading cause of vertebrate declines is human destruction of old growth forests, wetlands, chaparral, and other rich habitats. Worldwide, over two-thirds of the earth's habitable land surface has been significantly disturbed by human activities. Nearly half of the world's 233 primate species are threatened, largely because of their dependence on large expanses of tropical forest, a habitat under siege around the globe. In hotspots of forest loss, such as Madagascar, the Atlantic rainforest of eastern Brazil, and Southeast Asia, roughly 70 percent of primate species face extinction.
Habitat alteration is less visible but equally severe underwater.
40,000 large dams and hundreds of thousands of smaller barriers plug up the world's rivers, altering water temperatures, seasonal flow patterns and other conditions that support native fish. Some 36 seahorse species are threatened by the trade of an estimated 20 million seahorses each year-for use in traditional Chinese medicines, in the aquarium trade, and as tourist curios. In Central Africa, certain trees that rely on elephants to disperse their seeds failed to regenerate normally after elephant populations crashed from over-hunting. Invasive species are particularly devastating on islands and in isolated lakes and rivers, where native species are often unprepared to face tough exotic competitors. The study examines a number of possible routes for reversing these mounting species declines.