Forwarded from rom: Shyama Pagad
<[email protected]> on Aliens-L list server
Correspondence Nature Vol 475 July 7 2011
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Non-natives: 141 scientists object
We the undersigned feel that in advocating a
change in the environmental management of
introduced species (Nature 474, 153–154; 2011),
Mark Davis and colleagues assail two straw men.
First, most conservation biologists and
ecologists do not oppose non-native species per
se — only those targeted by the Convention on
Biological Diversity as threatening “ecosystems,
habitats or species”. There is no campaign
against all introductions: scarcity of resources
forces managers to prioritize according to the
impact of troublesome species, as in the Australian Weed Risk Assessment.
Second, invasion biologists and managers do not
ignore the benefits of introduced species. They
recognize that many non-native species curtail
erosion and provide food, timber and other
services. Nobody tries to eradicate wheat, for
instance. Useful non-native species may
sometimes still need to be managed because they
have a negative impact, such as tree invasions
that cause water loss in the South African fynbos.
Davis and colleagues downplay the severe impact
of non-native species that may not manifest for
decades after their introduction — as occurred
with the Brazilian pepper shrub (Schinus
terebinthifolius) in Florida (J. J. Ewel in
Ecology of Biological Invasions of North America
and Hawaii (eds H. A. Mooney and J. A. Drake)
214–230; Springer, 1986). Also, some species may
have only a subtle immediate impact but affect
entire ecosystems, for example through their effect on soils.
Pronouncing a newly introduced species as
harmless can lead to bad decisions about its
management. A species added to a plant community
that has no evolutionary experience of that
organism should be carefully watched.
For some introductions, eradication is possible.
For example, 27 invasive species have been
eradicated from the Galapagos Islands,
mitigating severe adverse effects on endemic
species. Harmful invasive species have been
successfully kept in check by biological, chemical and mechanical means.
The public must be vigilant of introductions and
continue to support the many successful management efforts.
Daniel Simberloff* University of Tennessee, Tennessee, USA.
[email protected]
*On behalf of 141 signatories
[<http://www.nature.com/nature/journal/v475/n7354/extref/475036a-s1.pdf>http://www.nature.com/nature/journal/v475/n7354/extref/475036a-s1.pdf]
(see go.nature.com/f1eqjn).
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Non-natives: put biodiversity at risk
Bias against non-native species is not
xenophobic (Nature 474, 153–154; 2011) — it has
a sound scientific foundation. The non-native
status of a species is highly relevant to
assessing its potential environmental and
economic impact. Unrestrained growth and
environmental damage follow when there are no
natural enemies in newly colonized areas. This
is not necessarily a sign of an invader’s
superior evolutionary fitness: it may lead to a
population collapse due to overexploitation of resources.
Non-native species can increase the variety of
species in a community, but it is an
oversimplification to equate this with increased
biodiversity, of which species richness is only
one component. Surviving populations of native
species may shrink or become restricted to
poor-quality marginal habitats. Such unevenness
hardly contributes to a more diverse community.
The genetic diversity of invaded communities may
decrease because of bottlenecks: native
genotypes disappear as populations fall, whereas
the invaders originate from very few initial colonizers.
Establishment of non-native species inevitably
decreases global diversity. Australia, for
example, was unique in having no placental
mammals; their introduction by humans made the
continent ecologically more similar to the rest of the world.
Andrei Alyokhin University of Maine, Maine, USA.
[email protected]
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Non-natives: plusses of invasion ecology
Contrary to the implications of Mark Davis and
colleagues (Nature 474, 153–154; 2011), invasion
ecology has given us valuable insight into the
effects of new species on ecological function
and into some of the precipitous changes we may face in the coming
decades.
Invasion ecologists generally assert that only a
very small fraction of non-native species harm
their new ecosystems. This position emerged as
early as 1986 and was mainstream in the era that
Davis and colleagues claim as the nadir of ecological nativism.
It is unfair to characterize any scientific
discipline solely by past failures and to ignore
its successes. Invasion ecology is making real
progress with defining impact and characterizing
risk. Let’s not throw up our hands in despair just yet.
Julie L. Lockwood Rutgers,
The State University of New Jersey, USA.
[email protected]
Martha F. Hoopes Mount Holyoke College, Massachusetts, USA.
Michael P. Marchetti California State University, California, USA.
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Non-natives: four risk factors
Mark Davis et al. set an unrealistically high
bar for those making management decisions about
exotic species (Nature 474, 153–154; 2011).
Control is often easier, cheaper and more
effective soon after detection (R. A. Haack et
al. Annu. Rev. Entomol. 55, 521–546; 2010). We
agree that research on ecosystem impact is
necessary, but such studies can take years.
Meanwhile, we suggest that control priorities
for potential invasive species could be based on
easily available data about natural history and
evolutionary ecology. We propose four guidelines
for identifying such invasives.
An exotic organism may be more likely to invade
and cause disruption the greater its rate of
reproduction; the greater its dispersal ability;
the closer (phylogenetically) its preferred food
in its native range is to an abundant taxon in
the new range; and the farther away
(phylogenetically) its predators and pathogens
are in its native range from those in its new range.
For example, the red turpentine beetle
(Dendroctonus valens) is not particularly
disruptive in its native range in North America
because it attacks only trees that are already
weakened. In China it attacks and kills healthy
trees (Z. Yan et al. Biodivers. Conserv. 14,
1735–1760; 2005). The reasons for this beetle’s
success as an invasive include its high
dispersal and reproductive rates, its affinity
for Chinese pines closely related to those it
feeds on ‘at home’, and the lack of predators or
pathogens phylogenetically similar to ones found in North America.
Manuel Lerdau Xishuangbanna Tropical Botanical
Garden, Chinese Academy of Sciences, Menglun,
Yunnan, China; and University of Virginia, Virginia, USA.
[email protected]
Jacob D. Wickham Institute of Chemistry, Chinese
Academy of Sciences, Beijing, China.
