| Hundreds of invasive species - from
rats to diseases - are posing one of the greatest threats to
wildlife around the world, conservationists have warned.
A study
of 57 countries, coordinated by the Global Invasive Species
Programme (GISP)
found that 542 types of animals and plants were putting native
wildlife at risk in places where they are not naturally found.
On average, around 50 non-native species are having a negative
impact on existing plants and animals in each country - ranging
from 9 in Equatorial Guinea, to a massive 222 in New Zealand.
On the list of invasive aliens are 316 plants, 101 marine
species, 44 freshwater fish, 43 mammals, 23 birds and 15 types
of amphibian - and the threat to native species from alien
invaders is growing, the experts warned.
Invasive plants and animals are those which threaten native
wildlife, by eating native species, laying eggs, damaging
their habitat, spreading disease or by competing with them
for the same 'niche' in an ecosystem.
Many invasive species are successful because they have no
natural predators in their new environment.
Examples of non-native species causing problems in the UK
include grey squirrels - whose spread has led to widespread
declines in red squirrels - the rampant plant Japanese
knotweed, American signal crayfish and water primroses.
The study said that, globally, the increase and spread of
invasive species is the result of a substantial rise in international
trade in the past 25 years. In some places, invasive species
are driving native wildlife towards extinction - for example
in New Zealand, where the yellowhead bird is now endangered
because of a surge in the number of rats, while the chytrid
fungus is spreading around the world causing massive declines
in amphibians.
There are examples of success stories, in which threatened
wildlife has bounced back after control measures were taken
against the invasive species.
On Mexico's Natividad Island, the black-vented shearwater
was at risk from the introduction of cats, goats and sheep,
but its numbers are now recovering following an eradication
programme.
In addition, control of the red fox in south Western Australia
has allowed the western brush wallaby to recover sufficiently
for it to be downgraded on the 'red list' of endangered
species compiled by the International Union for Conservation
of Nature (IUCN).
However, while most countries have made commitments to tackle
the threat of invasive species, only half have introduced
legislation and even fewer are taking enough action on the
ground, according to the IUCN.
Dr Stuart Butchart, from Birdlife International and one of
the authors of the study, said - "While some threatened species
on the IUCN red list have improved in status as a result of
successful control or eradication of invasive alien species,
a growing number are more threatened owing to increasing spread
and threats from non-indigenous species.
"This shows that, although we are winning some battles in
the fight against invasive species, current evidence suggests
that we are losing the war."
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