Hawaii

The Hawaiian Islands are one of the best examples of how isolation creates biodiversity, and of how human activity can destroy it.The islands are volcanic and are among the most isolated land on Earth, more than 3,000 km from the nearest continent. Very few species ever reached them, and each new arrival found many empty niches. The colonists evolved in isolation, often by adaptive radiation, so Hawaii has an extremely high level of endemism. Around 90% of its native flowering plant species are found nowhere else.Hawaiian honeycreepers are the best-known example. More than 50 species are thought to have evolved from a single finch-like ancestor. Their beaks vary greatly: thick, strong beaks for cracking seeds, thin curved beaks for probing flowers for nectar, and short beaks for catching insects.Since humans arrived, first Polynesian settlers and later Europeans, Hawaii's biodiversity has fallen sharply. Many honeycreeper species are extinct and most survivors are endangered. The causes include:1. Habitat loss, as native forest was cleared for farming and building.2. Introduced predators, such as rats, cats and mongooses, which endemic birds had not evolved defences against.3. Introduced disease: mosquitoes, which did not exist in Hawaii, now spread avian malaria. Many honeycreepers survive only in cool, high forests where mosquitoes are rare. As the climate warms, mosquitoes are spreading to higher altitudes.4. Introduced plants and grazing animals such as goats and pigs, which damage native vegetation.Hawaii shows why island endemics are so vulnerable: small ranges, small populations and no defences against introduced species.