|
|
 |
 |
|
|
The Hawaiian Archipelago -- An Ecosystem in Crisis
[Hawaiian Islands]
[The Origin of Hawaiian Life]
[Paradise Lost]
[Mosquitos and Malaria]
[The Biocomplexity Project]
The Hawaiian Islands
Shivering in the cold atop
one of Hawaii’s thirteen-thousand-foot volcanoes,
one can look down upon miles of alpine desert and sub-alpine
woodland, across an expanse of tropical rainforest and
dry forest, out over moon-like lava flows toward a ring
of coastal cliffs, beaches, and coral reefs. All of
these environments team with life, much of which is
found nowhere else on earth. But until relatively recently,
nothing existed here but a broad expanse of ocean. The
current “high” islands of Hawaii originated
as a chain of fiery volcanoes that began to emerge from
the depths of the central Pacific Ocean about 6-7 million
years ago.
|
 |
The Source of Hawaii's Diversity
The process of "Adaptive radiation" allowed
a small number of immigrants to evolve into hundreds
of new species, found only in Hawaii.
Flowering Plants |
270 Species |
|
960 Species |
Ferns and Fern Allies |
135 Species |
|
168 Species |
Insects and Allied Forms |
300 to 400 Species |
|
6,000-10,000 Species |
Land Snails |
|
|
1,200 Species |
Land Birds |
20 Species |
|
|
*
** |
Probably carried by birds.
Some of these have since gone extinct,
and we only have their fossils. |
|
|
These mountains of volcanic rock,
isolated by almost three thousand miles of ocean in
every direction, were completely separated from the
rest of the world. As they emerged, these islands began
to be settled by the few plants and animals hardy enough
to survive the journey. Seabirds and shorebirds may
have been among the first vertebrate arrivals, perhaps
bringing with them and depositing the seeds of recently
eaten plants. The seeds of some plants attached themselves
to the birds plumage and “hitchhiked” to
the islands, whereas other plants have seeds so small
that they could easily be blown across the ocean by
the wind. Many invertebrates, such as spiders and insects,
likely arrived in the islands by the wind as well. Over
time, some of those animals and plants that survived
the journey evolved into many new species through a
process known as “adaptive radiation”.
|
The Origin of Hawaiian Life
The story of the Hawaiian honeycreepers is an outstanding example
of how the Hawaiian islands became home to countless
forms of unique life. About 3-4 million years ago, a
small flock of cardueline finches arrived in Hawaii,
probably blown in on a storm from North America. With
few competitors and countless environments with many
different types of food, Hawaii was ripe for colonization.
As the new colonists spread out over the islands, individual
populations became isolated from one another and began
to evolve in different ways. Some evolved long, curved
bills to extract nectar from flowers, others evolved
short, stout bills for crushing hard seeds. By the time
Polynesians arrived about 2000 years ago, they found
over 50 unique species and subspecies of honeycreepers
- all descended from that one original group.
|
Original art © H. D. Pratt, Louisiana State University
Museum of Zoology
|
|
Paradise Lost
Although the Hawaiian Islands rested alone in the Pacific for millions
of years, the arrival of mankind permanently broke Hawaii’s
isolation. Starting around 400 AD when Polynesian sailors
first colonized the islands, humans began to carry foreign
species across the ocean. Some of the early arrivals were
dogs, pigs, jungle fowl, rats, and various reptiles and insects.
Many types of plants were introduced to support early Hawaiian
agriculture, textiles, and musical instrument construction.
Hawaiians also began to clear lowland forests for farming,
hunt native birds for food and plumage, and raid offshore
sea-bird nests for eggs. All of these practices began to have
an impact on Hawaii’s ecosystem. Some estimates say
that over half of Hawaii’s unique bird species had gone
extinct before Europeans arrived to record them.
Captain Cook’s arrival in 1778 only accelerated the
process of introducing species to Hawaii. As European sailing
ships started a constant traffic to and from the islands,
stowaway animals and deliberate introductions carried a constant
stream of invasive species. Several new species of rats were
introduced, which immediately began to eat plants and sometimes
even bird eggs. The mongoose was introduced to combat rats,
but immediately preferred to prey on native birds instead.
An estimated 900 different species of plants were introduced--Hawaii
had no conifers (pine trees, fir trees, etc) until they were
introduced by Europeans. All of these new species immediately
began to compete with native species, and the native species
almost always were the losing end of the battle. For honeycreepers,
however, one of the most destructive new inhabitants was the
mosquito.
Mosquito and Malaria
Before Europeans arrived, Hawaii had no mosquitoes or other bloodsucking
flies. For humans and animals alike, this meant no annoying
bites and more importantly, no mosquito-borne diseases. However,
the first mosquito species was introduced in 1826, and over
the next hundred and fifty years, at least four more species
arrived. It is thought that sometime in the 1800’s,
the first of two mosquito-transmitted avian diseases was introduced
to the islands--avian pox virus. This pathogen causes
large tumor-like swellings on the feet and legs and around
the eyes and beak of infected birds and is transmitted on
the mouthparts of mosquitoes, in effect making them “flying
needles”. Early naturalists in the islands reported
the first large scale epidemics in native bird populations
in the late 1800’s, but it wasn’t until the early
part of the 20th century that we think that the second pathogen,
a species of avian malaria (Plasmodium relictum) reached Hawaii.
Similar to human malaria in many aspects of its life cycle,
avian malaria probably reached the islands in imported cage
birds that were released to replace declining native birds.
With mosquito vectors already in place, it is likely that
avian malaria spread quickly into native birds. With no prior
exposure or natural immunity to this disease in native species,
we think that it probably swept through remaining lowland
native bird populations, further hastening the extinction
of several species and decline of many more. Only high on
the volcanoes, where colder-temperatures limit the spread
of mosquitoes, do native forest bird communities remain relatively
intact.
The Biocomplexity Project
The Biocomplexity Project is attempting to unravel the complexities and
impacts of introduced pox virus and avian malaria in native
forest bird populations with the hope of developing long-term
strategies for preventing further extinctions of threatened
and endangered native birds and restoring them to habitats
where they were formerly common. The story of native birds
being pushed into the highest reaches of the mountains by
mosquitoes is just one example of the dynamics we are only
just beginning to understand--feral pigs are digging
up forests and creating breeding sites for mosquitoes, suburban
development is eliminating large areas of lowland native forest,
and the pathogens and hosts themselves may be undergoing natural
selection and coevolutionary changes. At the same time, we
hope that getting a clearer picture of a single environment
like Hawaii where so much environmental and climatic diversity
is squeezed into a small geographic area will give us knowledge
that we can apply to other environments. Possibly we can learn
enough about malaria to help control its spread elsewhere;
possibly we can learn enough about the Hawaiian forests to
help protect forests elsewhere. Hawaii is an environment that
we hope will teach us more about not only Hawaiian ecosystems,
but about the world in general.
|
|
 |
|
