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Bio-invasion is now thought to be the second gravest threat to biodiversity
in North America, after habitat destruction and degradation (CEC 2000).
Competition or predation by non-native species imperils nearly half of
the species listed as threatened or endangered under the US Endangered
Species Act (Wilcove and others 1998). In Canada, alien species have been
involved in causing risk to about 25 per cent of endangered, 31 per cent
of threatened and 16 per cent of vulnerable species (Lee 2001).
| Restoration of the Florida
Everglades |
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The Everglades is the central part of a 23 000 km2 watershed covering
the lower third of Florida. In the early 1900s, large tracts were
drained and water supplies reconfigured. Protected from flooding
by levees and canals, South Florida became home to six million people
along the Miami-Palm Beach corridor and an important sugarcane,
fruit and vegetable producer (UNDP, UNEP, World Bank and WRI 2000).
Originally stretching over 11 650 km2, nearly half of the Everglades
wetlands have been lost, reducing the amount of freshwater flowing
to the coast, disrupting salinity levels and altering the natural
capacity of the ecosystem to store and release water. The state
of the Everglades deteriorated most rapidly over the past two decades
with sea grass die-offs, the invasion of non-native species, nutrient
contamination, large algal blooms in Florida Bay and declines in
fishing harvests and some bird populations (UNDP, UNEP, World Bank
and WRI 2000).
Regional efforts to address the problems began in the early 1980s
but it took until 1998 for all parties - the sugar industry, environmentalists,
real estate developers and American Indian tribes - to come together
in support of a comprehensive plan to restore and preserve the Everglades.
Developed by the Army Corps of Engineers, it is the world's most
ambitious and extensive wetlands restoration effort, costing the
federal government US$7.8 billion. It will take more than 20 years
to complete (Alvarez 2000, Army Corps of Engineers 2000).
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Invasive aquatic species are particularly threatening to wetland and
freshwater ecosystems (see box below) and can also pose serious health
risks. For example, human cholera bacteria were found in ballast tanks
and in oyster and fin-fish samples in Mobile, Alabama, in 1991 (ANS 2000).
Alien aquatic species are expected to contribute to the extinction of
native freshwater species in North America at a rate of 4 per cent a decade
over the next century (Ricciardi and Rasmussen 1999).
| Bio-invasion |
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Bio-invasion is the influx of alien invasive species. Alien species
are considered invasive when they become established in natural
habitats, are agents of change, and threaten native biological diversity.
Alien invasive species include bacteria, viruses, fungi, insects,
molluscs, plants, fish, mammals and birds (IUCN 2001).
Species that become invasive can be introduced either intentionally
or unintentionally through pathways (or vectors). These include
transportation (by water, land and air; in the goods themselves,
in dunnage, packing materials or containers, in or on ships, planes,
trains, trucks or cars); agriculture; horticulture and plant nursery
stock; aquaculture industry; live food fish industry; bait fish;
ornamental pond, water garden and the aquarium pet trades. Where
there are no natural predators, they can come to dominate ecosystems,
and can alter the composition and structure of food webs, nutrient
cycles, fire cycles, and hydrology and energy budgets, threatening
agricultural productivity and other industries dependent on living
resources (Alonso and others 2001).
As an example, purple loosestrife (Lythrum salicaria), which was
introduced from Europe in the mid-1800s as a garden ornamental,
has been spreading in North America at a rate of 115 000 ha a year,
invading wetland habitats where it dominates native plants and deprives
waterfowl and other species of food sources (Haber 1996, Pimentel
and others 1999). When non-indigenous aquatic weeds such as purple
loosestrife, Eurasian water milfoil and hydrilla replace native
species, they establish dense colonies that can impair navigation,
water-based recreation and flood control; degrade water quality
and wildlife habitat; accelerate the filling of lakes and reservoirs;
and depress property values (Haber 1996).
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The high economic costs of damage caused by bioinvasions in North America
is causing increasing concern. Both countries have developed monitoring
plans and information systems to help control bioinvasion (Haber 1996,
Kaiser 1999).
Responses to the challenge of invasive species include legislation, policies,
and plans and programmes that focus on preventing the invasion of new
species and the eradication or control of established ones. Canada and
the United States cooperate in programmes related to invasive species
in the Great Lakes, for example. Despite requirements for ships to exchange
ballast water at sea, however, the influx of new species into the Great
Lakes continues and is considered to be a serious threat to the integrity
of the Great Lakes ecosystem.
As trade increases, new invasions are expected. In addition, it may be
that global climate change could create conditions that are even more
conducive to bioinvasion (Holmes 1998). North American as well as global
cooperation is essential to stem the tide of bioinvasion and the damage
it causes.
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