An engine of evolution
The Peak Wilderness Sanctuary, a UNESCO World Heritage site in Sri Lanka's central highlands, demonstrates adaptive radiation. This is an evolutionary process where organisms rapidly diversify from a common ancestor. In these mountains, the primary species in this process are the shrub frogs of the genus Pseudophilautus. The ancestors of these frogs are thought to have migrated from India around the Eocene-Oligocene boundary, and in the isolated, stable environment of Sri Lanka's wet highlands, they diversified into a vast array of species.
The terrain itself is the source of this diversity. The sanctuary consists of a series of cool, wet mountain ranges separated by warmer, drier valleys. These "sky islands" isolate frog populations, preventing gene flow and allowing them to evolve independently. Over millions of years, this isolation has resulted in extreme specialization. Researchers have identified different "ecomorphs"—frogs adapted to specific microhabitats like leaf-litter, rock boulders, and high canopies. This intense speciation means that of the more than 120 amphibian species in Sri Lanka, about 90% are endemic, found nowhere else on Earth. Many of these are "point endemics," with ranges restricted to a single mountainside or forest patch.