Why do the Pacific Islands have so many endemic species?

The high number of endemic species in the Pacific Islands is primarily the result of adaptive radiation, a process where organisms evolve rapidly from a single ancestral lineage to exploit diverse ecological niches.12

When colonizing species reach remote, geographically isolated archipelagoes, they often encounter environments with few competitors and an abundance of unoccupied niches. Because these islands are far from continents, populations become physically separated, leading to allopatric speciation. Over time, these populations evolve independently, developing unique morphological and ecological traits that allow them to adapt to specific local conditions.13

This phenomenon is particularly striking in the Hawaiian archipelago, where the extreme isolation and volcanic origins of the islands have fostered an extraordinary level of endemism. For example, a single immigrant bird species can diversify into numerous distinct species of honeycreepers, each adapted to different diets and habitats. Similar patterns are observed across the broader Polynesian subkingdom, where high numbers of endemic taxa have developed in relative isolation.124