Re: Fwd: Alien Species Often Fit In Fine, Some Scientists Contend

From: Philip Jonkers (
Date: Wed Sep 05 2001 - 15:22:57 BST

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    Subject: Re: Fwd: Alien Species Often Fit In Fine, Some Scientists Contend
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    Date: Wed, 05 Sep 2001 16:22:57 +0200 (CEST)
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    Quoting "Wade T.Smith" <>:

    > Alien Species Often Fit In Fine, Some Scientists Contend
    > By MARK DERR
    > Governments, private groups and individuals spend billions of dollars a
    > year to root out non-native organisms that are considered dangerous to
    > ecosystems and to prevent the introduction of new interlopers.
    > But a number of scientists question the assumption that alien species
    > are
    > never acceptable in a natural ecosystem. While applauding efforts to
    > banish harmful organisms ? like the brown tree snakes that have
    > destroyed
    > most of Guam's native species of forest birds or the star thistle, a
    > prickly weed that is toxic to horses and has invaded much of the West ?
    > they say portraying introduced species as inherently bad is an
    > unscientific approach.
    > Distinctions between exotics and native species are artificial, said Dr.
    > Michael Rosenzweig, a professor of evolutionary biology at the
    > University
    > of Arizona, because they depend on picking a date and calling the plants
    > and animals that show up after that exotic. Ecosystems free of species
    > defined as exotic are, by default, considered the most natural.
    > "You can't roll back the clock and remove all exotics or fix habitats,"
    > Dr. Rosenzweig said. "Both native and exotic species can become
    > invasive,
    > and so they all have to be monitored and controlled when they begin to
    > get out of hand."
    > At its core, the debate is about how to manage the world's remaining
    > natural ecosystems and about how, and how much, to restore other
    > habitats. Species that invade a territory can harm ecosystems,
    > agriculture and human health. They can destroy some native species and
    > supplant or threaten others. Next to habitat loss, these invasive
    > species
    > represent the greatest threat to biodiversity worldwide, many ecologists
    > say.
    > Ecologists generally define an alien species as one that people
    > inadvertently or deliberately carried to its new location. In the New
    > World, exotic species are those introduced after the first European
    > contact. That date, rounded off to 1500, represents what ecologists
    > consider to have been a major shift in the spread of species, including
    > crops and livestock, as they began to leapfrog with humans from
    > continent
    > to continent.
    > Only a small percentage of alien species cause problems in their new
    > habitats, said Dr. Daniel Simberloff, a professor of ecology and
    > evolutionary biology at the University of Tennessee. Of the country's
    > 7,000 alien species ? out of a total of 150,000 species ? only about 10
    > percent are invasive, he said. The other 90 percent have fit into their
    > environments and are considered naturalized. Yet appearances can
    > deceive,
    > ecologists caution, and many of these exotics may be considered
    > acceptable only because no one has documented their harmful effects. And
    > non-native species can appear innocuous for decades, then turn
    > invasive.
    > One example is the Brazilian pepper, which landscapers introduced into
    > South Florida in the late 19th century. It started to spread widely in
    > the 1950's and has now crowded out native vegetation throughout the
    > Everglades. Once a species begins to run amok, it is extremely difficult
    > to eradicate.
    > Faced with such uncertainty, many ecologists argue for strong steps. "I
    > think we should take a precautionary approach and be much more proactive
    > in trying to take these things out before they become problems," Dr.
    > Simberloff said. "You don't want exotics in natural ecosystems."
    > But a number of experts question the scientific wisdom of trying to roll
    > back ecosystems to a time when they were more natural.
    > Defining which species belong in an ecosystem is based less on science
    > than on historical, cultural, moral, geographic and theological
    > arguments, said Dr. Mark Sagoff, who studies the issue at the University
    > of Maryland's Institute for Philosophy and Public Policy. Science cannot
    > judge an ecosystem with exotics to be worse, or less natural, than one
    > without them, he said, without also taking into account the effects of
    > those species on their environments.
    > Even many ecologists who would like to rid ecosystems of all exotics
    > admit that the goal is impractical.
    > "We can't return to pre-settlement ecosystems," said Dr. Alan Holt, the
    > director of conservation programs for the Northwest and Hawaii at the
    > Nature Conservancy, a nonprofit group that acquires and restores land to
    > preserve the diversity of species. For one thing, he said, many exotic
    > species have become so integrated into ecosystems that animals, some
    > endangered, rely on them for food and shelter.
    > Dr. Rosenzweig said removing exotics might cause other problems. In
    > Australia's Northern Territory, for example, the eradication of the non-
    > native water buffalo that were ravaging vegetation led to the explosive
    > growth of a little-noticed plant, the giant mimosa, which was introduced
    > from Central America in the 1890's. The shrub has been more destructive
    > and harder to remove than the water buffalo.
    > In the March issue of the journal Evolutionary Ecology Research, Dr.
    > Rosenzweig, the editor, challenges the prevailing view that invasive
    > alien species reduces biodiversity. The exotics increase the number of
    > species in the environment, he wrote. Even if alien species cause
    > extinctions, the extinction phase will eventually end and new species
    > may
    > then begin to evolve, he explained.
    > Ecologists should focus on managing the environments that include exotic
    > immigrants, Dr. Rosenzweig said, and creating new ones where necessary
    > to
    > enhance species' survival and biodiversity.

    It seems that natural selection is given a new boost by
    increasing the levels of competition through man's agency,
    to quote Darwin. Live and let live I say.... As humans, let's
    not waste time and energy in the hope of setting back the clock.
    These efforts will be futile as we humans do not have
    absolute authority to do so.

    Through humans' transport activities alien species spread
    and may or may not grab hold of native species' niches.
    It's up to the fitness difference of the invading and
    domestic species what the outcome will be. The introduction
    of new species will trigger off a temporary disturbance
    in the relations between native species themselves
    and between the native and invading species. Ultimately,
    the more vigorous will prevail and a new balance will be
    brought about. As the article shows this is accompanied
    by environmental changes. As long as there are no immediate
    threats to the health of humans, what's wrong with that?



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