Life on the Edge

Even though rain forests cover less than a tenth of Earth’s surface, they harbor nearly half the world’s 5 million or so species of plants and animals. How that diversity became concentrated in so circumscribed a habitat remains a mystery, yet biologists and conservationists alike assume the source of the rain forest’s burgeoning variety must lie, like its greatest density of species, in the forest’s deep interior. But now a team of biologists has found that diversity in some cases emerges not at the forest’s center but at its margins, where dense vegetation meets grassy savanna.