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Dispersal Located more than 2,000 miles from the nearest large land mass, the Hawaiian Islands are the most isolated high islands in the world. This extreme isolation made it very difficult for plants and animals to colonize the Islands. Many insects probably froze in the jet stream, seeds undoubtedly absorbed salt water and were no longer viable, and a number of birds probably died over the wide expanse of ocean. Hawaiian terrestrial environments were colonized by plants whose seeds were tolerant to salt water or small enough to be carried in the wind or in a bird's digestive tract. Seeds and snails that could stick to a bird's feathers or float on a raft of vegetation, as well as animals that could fly or be carried in the wind, such as birds, bats, small insects and spiders, were also among the successful colonizers. The marine environment was colonized by animals, including turtles, monk seals, fishes and mollusks that swam or drifted to the Islands. Hawaiian fresh water organisms drifted on ocean currents and probably evolved from the larvae of similar species inhabiting streams on high islands elsewhere in the Pacific. Many of the major families of organisms found on continents did not successfully colonize the islands. For example, no large mammals (cows, pigs, deer, goats etc.), lizards, or frogs are native to Hawai`i. Native Plants and Animals Plants and animals that reached Hawai`i without human assistance are referred to as native. Those that evolved to be unique to Hawai`i, such as the happy-face spider, are endemic. Those that still occur in other areas, such as the coastal naupaka bush that is found on the Hawaiian Islands and elsewhere in the Pacific, are indigenous. Approximately 90% of native Hawaiian plants and animals are endemic and unique to our Islands! Adaptation Descendants of native colonizing plants and animals adapted to the variety of ecological opportunities in Hawai`i. The stable climate of the Islands, combined with a wide range of topography and elevation creates a variety of microclimates, such as those found in rainforests, dry forests, and alpine deserts. These microclimates offered a number of habitats to colonized species and a range of opportunities for their descendants. Scientists studying Hawaiian plants and animals have discovered that descendants of some species that were adapted to one environment, gradually shifted to take advantage of new environments. For example, some descendants of insects that were adapted to rainforest conditions lost eyesight and coloration as adaptation to life in dark lava tubes. Descendants of another forest insect developed adaptations to conditions on the highest, cold summits of the island of Hawai`i. Native stream fishes, prawns and snails are adapted to freshwater conditions, but their ancestors lived in the sea. Introduced Plants and Animals Prior to the arrival of people, all plants and animals in Hawai`i were native species. Today, plants and animals introduced by people, dominate Hawaiian lowland environments. Some species were introduced intentionally, such as the mongoose that was brought in to control rats in sugarcane fields. Other species, such as the mosquito that arrived in Hawaiian streams as larvae from a ship's water barrel, were introduced accidentally. When a non-native plant or animal is introduced without its natural controls, such as diseases or insects, it can upset the balance of native ecosystems. For example, the mejiro (Japanese white-eye) bird is now commonly found in forests where it competes with native species for habitat. Due to the impact of introduced species and other disturbances to habitat, many native plants and animals are now found only in remote areas of Hawai`i. In these special places, human observers can gain insights into the remarkable evolution of a diverse array of species found nowhere else on Earth.
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