This relative of the famed
silversword, Wilkesia gymnoxiphium, grows abun-
dantly in this field on the
rim of Kauai's Waimea
Canyon.

Pain in paradise
For more than a century, ever since artists like Paul Gauguin and authors like Robert Louis Stevenson wandered the Pacific, the Polynesian islands have symbolized natural bliss. Often considered a tropical paradise, these islands equally represent paradise lost -- the ongoing wave of extinctions that

Hawaii is the northernmost archipelago in Polynesia.

many biologists think will eventually rival the extinction that squelched the dinosaurs 65 million years ago. "Future generations will have difficulty distinguishing this from an asteroid strike," says Paul Alan Cox, director of the National Tropical Botanical Garden.

For a variety of factors related to isolation, islands are citadels of both evolutionary diversity and extinction. And in fact, the same forces that cause species to attain so many forms can make them prone to extinction.

Many of the forces that affect island biodiversity can be thought of as the biology of small numbers:

Founder principle. When only a few organisms establish a population, they cannot represent the entire genetic diversity of a species in its home territory.

Genetic drift. If a plant has a population of 10,000, and half are killed, chances are that the remaining 5,000 will carry a good genetic representation of the original population. But half of only 10 plants survive, chance dictates some of the remainders will carry weirdo genes.

Bottlenecks. A related effect takes place when a population drops close to zero -- goes through a bottleneck. Genes that could help in the future disappear, leaving less ability to adapt to change.

Adaptive radiation. 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. Many plants require pollinators -- animals such as insects, birds and bats -- to transfer pollen (male reproductive bodies) to fertilize their eggs. So when pollinators like the flying fox, a giant bat in Samoa, are hunted to extinction, their reproduction ceases. Unlike many native plants, many alien invaders can either fertilize themselves or reproduce without sex..

A wild assemblage Taken together, these island effects help explain both the incredible diversity of Hawaii, and its extinction crisis. Let's look at biodiversity first. If you already know the standard rap on biodiversity, skip some paragraphs. Otherwise, read on.

Biodiversity is valuable because:

It's the stuff of life. Each genetic lineage has been adapted by evolution to a specific location and set of circumstances -- to a specific ecological niche. In other words, it represents a unique form of life, a unique solution to the linked problems of survival and reproduction.

Unique life forms have unique abilities -- as the drug industry knows well. Fifty-seven percent of the top 150 drugs in the United States are derived from biodiversity, according to Cox, who studies how people use plants.

Diversity can also be beautiful -- as witnessed by almost any flower.

Finally, unique plants are valuable for themselves. "I believe all things have a right to exist whether they are useful to me or not," says botanical collector Ken Wood.

If you want to see strange plants and animals, Hawaii is your place. Fruit flies -- the little buggers that obsess geneticists and bother fruit farmers in almost equal measure -- are rampant on the islands, with roughly 1,000 species. Likewise, members of the Lobelia genus, one of the early plants to arrive here, have adapted to occupy highlands and lowlands, wetlands and drylands. A genus of palms, Pritchardia, is found here too, with plenty of unusual variations -- and plenty of nearly-extinct species.

Unpleasant upshot
Enter Homo sapiens, and everything changed. About 2,000 years ago, the Polynesians brought plants, pigs and agriculture to the islands. Plants like ti, used for ceremonies and food, and shampoo; ginger, used for the obvious purpose, started to spread as farms displaced lowlands forests.

The pace of change accelerated in 1778, after Captain Cook "discovered" the archipelago (at least as far as Europeans were concerned). Suddenly, a wave of new species and technologies drastically raised the threat to native species.

Worse yet, many of the newcomers are generalists that can carpet entire valleys, like the strawberry guava tree. Others, like the black rat or mongoose, prey on native birds.

What's the story with these aliens?