IS AN ENVIRONMENTAL PARADISE AND PARADOX
by Whit Gibbons
January 30, 2005
more plants and animals today are found in regions beyond their natural
range. Betsie Rothermel, research ecologist at the Savannah River Ecology
Laboratory, provides an intriguing perspective of an environmental dilemma
resulting from animal introductions. The following is Betsie's account
of her winter holiday in Maui, as seen through the eyes of an ecologist.
time I visit Hawaii, I am treated to an outstanding nature experience.
In past visits, I swam with wild dolphins and snorkeled with sea turtles.
This time I watched humpback whales and interrupted some spawning toads.
Allow me to explain. . . .
and nonmarine reptiles do not occur naturally in Hawaii. Whereas some
insects, birds, plants, and even a mammal (a bat) drifted or were blown
to the islands and diversified into new forms, amphibians and reptiles
(herps) simply never crossed the vast expanse of ocean to colonize this
isolated chain of islands. But because of accidental or deliberate introductions
by people, more than two dozen nonnative species of herps now live in
the Hawaiian Islands.
‘Iao (pronounced ee-ow) Valley is a steep-sided, mist-shrouded ravine
in the heart of the West Maui Mountains. The road into ‘Iao dead-ends
in a park with trails to a scenic lookout and patches of taro (a vegetable
introduced to Hawaii by Polynesian settlers more than a thousand years
ago) growing in pools of water diverted from the stream. Busloads of tourists
come here daily. While circling one of the pools, something strange caught
my eye--long, gelatinous strings enclosing tiny black beads, criss-crossing
the bottom of the pool and entwined in clumps of vegetation. Toad eggs!
My eyes settled on a large shape in the water. Aha! A giant toad. In fact,
not just one toad, but a huge female with her mate clasped securely to
her back, sitting motionless on the bottom of the pool.
adult giant toad is an impressive sight. Picture your garden-variety southern
toad on steroids. Giant toads can grow up to nine inches long and weigh
up to three pounds. Giant toads (also known as cane toads) were introduced
to Hawaii by sugarcane growers in the 1930s, in hopes they would control
insect pests, an approach with questionable effectiveness. These two were
the largest specimens I had ever seen, and my excitement soon attracted
a small crowd. While taking photos, I explained how giant toads have managed
to invade many areas outside their native range in tropical America. This
one female would lay up to 30,000 eggs, which would soon hatch into tiny
black tadpoles that would feed voraciously on algae, grow quickly, and
metamorphose into toadlets smaller than a dime. I pointed out the paratoid
glands on their head, which secrete a milky, toxic substance if the animal
is attacked. Even the eggs and tadpoles are toxic to predators. Combine
productivity and invincibility with a flexible diet, and you have the
formula for a very successful invader.
the excitement over the toads was dying down, someone spotted a small,
dark lizard on a downed branch. I concluded it was a metallic skink, a
native to Australia. Then we saw another, better-camouflaged lizard sitting
only inches away. I recognized this one instantly--a green anole, the
species found in the southeastern United States. Thus within 20 steps,
I found toads from South America, a skink from Australia, and a lizard
from the U.S. mainland, none of which belonged on this volcano in the
middle of the ocean.
and especially herpetologists, in Hawaii must be plagued by mixed emotions--admiration
for these amazing animals, tempered by apprehension about their potential
effects on the fragile island ecosystems and endemic fauna. The question
is, how harmful are these 'invaders'? Abundant amphibians might compete
with birds or invertebrates for insect prey. Introduced reptiles undoubtedly
prey on native wildlife. Combined with habitat loss and other factors,
this could drive more species to extinction, something Hawaii does not
need; the islands have already lost more than half of their native birds
since colonization by humans. I left ‘Iao thinking about the potential
downside of being a herpetologist in Hawaii, a job that might require
eradicating one’s favorite animals."
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