The series of ice ages that occurred between 2.4 million and 10,000 years ago had a dramatic effect on the climate and the life forms in the tropics. During each glacial period the tropics became both cooler and drier, turning some areas of tropical rain forest into dry seasonal forest or savanna. For reasons associated with local topography, geography, and climate, some areas of forest escaped the dry periods, and acted as refuges (refugia) for forest biota. During subsequent interglacials, when humid conditions returned to the tropics, the forests expanded and were repopulated by plants and animals from the species-rich refugia.

Ice age refugia today correspond to present day areas of tropical forest that typically receive a high rainfall and often contain unusually large numbers of species, including a high proportion of endemic species. These species-rich refugia are surrounded by relatively species-poor areas of forest. Refugia...