Isolated in the mid Pacific, the Hawaiian Islands are the most remote major island group on Earth. They were formed as the Pacific Plate moved across a volcanic "hot spot" within the earth's mantle. Lying 2,400 miles (3,862 km) from the nearest continent, they have never had connection to any other land mass. Natural crossings across this great expanse of ocean by animals and plants were extremely rare and very surprising occasions. After such accidental arrivals, and isolated from mainland populations, these pioneer organisms took strange courses of evolution and allowed a unique biota to develop.
Unaccustomed to mainland competition, however, these remote native island ecosystems are defenseless against mainland alien species, and have been decimated by new grazers, predators and diseases.