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
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
is the northernmost archipelago in Polynesia.
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.
of the forces that affect island biodiversity can be thought of as the
biology of small numbers:
principle. When only a few organisms establish a population, they cannot
represent the entire genetic diversity of a species in its home territory.
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.
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.
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.
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..
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.
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.
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
Kauka, an educator in traditional Hawaiian culture, examines a tree
whose bark will make tapa cloth.
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.
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.
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
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.
the story with these aliens?