NOT LET THE ALIENS TAKE OVER?
by Whit Gibbons
April 15, 2007
invading the world. You would be hard pressed to find any substantial
land area anywhere that is not under siege by at least one form of alien
life. But these aliens have not come from outer space but from our own
of introduced exotics causing someone some kind of problem somewhere is
immense. Some are old and familiar--rabbits in Australia, fire ants in
the South, brown tree snakes on Guam. Introduced rats destroy native wildlife
on islands throughout the world. Kudzu and chestnut blight are species
that most people wish had never left their native habitats. Some U.S.
invaders are relatively recent arrivals, such as Burmese pythons in the
Everglades and killer bees in Texas.
plants and animals come from places all around the globe. The Eurasian
tamarisk tree has invaded California deserts; South American water hyacinth,
Australian pine, and Brazilian pepper have dramatically altered southern
Florida; European invaders such as zebra mussels and the purple loosestrife
plant are inflicting widespread natural and economic damage elsewhere.
Alien species reportedly cost our country more than $100 billion dollars
intentionally or accidentally introduced, nonnative species can become
pests when no natural enemies are present to control their numbers. Through
competition or outright predation, these species alter habitats and community
structure, often eliminating some native flora and fauna. A common concern
with invasive plants is that the introduced species will take over a habitat
and crowd out naturally occurring plants.
But is a
habitat necessarily ruined simply because one or more species dominate
the others? The seemingly endless acres of coastal salt marsh grass are
not viewed as aberrant. Nor have the miles and miles of native prairie
grasses that once populated the Great Plains been considered unacceptable.
As evolution accompanies environmental changes, the relative abundance
of species changes. Some are successful; some are not; and many are relegated
to minor roles in a habitat.
we do when we realize that yet another introduced species is taking hold?
What if we didn't do anything? What if we abandoned our attempts at eradication
and simply accepted the new order of ecosystems and their changing array
of species distributions, both native and introduced? Evolutionary processes
will continue to operate as they have for the past billion years, ultimately
resulting in a different composition of species.
some people view investing time and money to fight introduced exotics
as a hopeless exercise, others would not even consider the option of just
letting the aliens have their way without trying to stop them. The idea
of taking no action against potential extinctions of native plants and
animals because of an alien species is anathema to many environmentalists.
But are we winning a few battles while losing the war against alien species?
Are the environmental benefits of preventing and controlling alien invasions
worth the economic costs?
an introduced species will be challenged and efforts made to eliminate
it often depends on who or what is affected and how much political clout
the affected parties have. For instance, the aquatic weed hydrilla was
introduced into U.S. lakes from Africa, presumably through the home aquarium
trade in the 1960s. Hydrilla is likely to have high levels of taxpayer
dollars dedicated toward its eradication. True, the plants compete with
native species, but that alone would not merit all-out war. These weeds,
however, clog outboard motors of people engaged in recreational water
many introduced species have become an integral part of our culture and
society. The European honeybee almost certainly competes with native bees
for pollen but is considered desirable. Likewise, hundreds of popular
horticultural plants are nonnative species whose continued existence is
not merely tolerated but encouraged.
Introduced exotic species clearly create a dilemma. What should we do
to combat what is becoming a national problem? Should we do anything?
Dov Sax of the University of Georgia is a well-known research scientist
who has conducted research on invasive species. I asked him for his perspective
on exotic species invading the country. His answer will appear next week.
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