Life arrived on most other islands by accident or by drift. Some plants arrived by air transport; seeds carried in the digestive tracts of birds account for nearly 40 percent of Hawaii's early plants. The first invaders were either creatures that could float well enough, in air or water, to cross stretches of ocean, or those whose seeds could survive a voyage in some bird's gut. At times of lower sea level, land bridges linked, or nearly linked, many islands in the far western Pacific, so some species colonized these islands without being notably good floaters or stowaways. In the eastern Pacific (Easter Island, for example) only the best floaters and travelers arrived and survived. Consequently, the western islands have far more species and far greater biodiversity than do the eastern islands of Polynesia. Mammals found it hard to get anywhere in the island Pacific; only bats and rats successfully colonized east of New Guinea. Almost all species derive from Asia; the early Pacific was an Asian lake, with only a tiny proportion of species from the Americas. As a rule of thumb, the further from Indonesia, the more impoverished the plant and animal life and, in consequence, the less stable and resilient in the face of disturbance. This attenuation is strong for land species, less strong for marine species, and nonexistent for oceanic birds, although fairly strong for land birds.
