The early organisms to reach virgin land find many ecological niches open. The volcanic Hawaiian Islands emerged from the waves utterly barren. Some descendants of the first birds to reach the islands started eating nuts, and evolved the needed stout bill. Others began drinking flower nectar, and evolved a long, slender bill. Lack of competition.
Many plants protect themselves against grazing animals with thorns and poisonous chemicals.
But before the Polynesians arrived the only land mammal in Hawaii was a bat, so many plants lost these defensive adaptations. Now, an invasion of feral goats and pigs is making mincemeat of those defenseless but tasty native plants. Relationship with pollinators. So when pollinators like the flying fox, a giant bat in Samoa, are hunted to extinction, their reproduction ceases. A wild assemblage Taken together, these island effects help explain both the incredible diversity of Hawaii, and its extinction crisis.