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| February 2010 |
Feature |
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Impact of nature’s invading aliens measured for
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 A large grove of eucalypts on the Kariega river dwarfs this vehicle |
Invasive Alien Species,
ranging from disease and plants, to rats and goats, are one of the top three
threats to life on this planet, according to a new publication coordinated by
the Global Invasive Species Programme (GISP), of which IUCN is a partner.
Most countries have made international commitments to tackle this threat, but
only half have introduced relevant legislation and even fewer are taking
adequate action on the ground.
The publication, “Global indicators of biological invasion: species numbers,
biodiversity impact and policy responses”, looked at 57 countries and found
that, on average, there are 50 non-indigenous species per country which have a
negative impact on biodiversity. The number of invasive alien species ranged
from nine in Equatorial Guinea to 222 in New Zealand.
A total of 542 species were documented as invasive aliens, including 316
plants, 101 marine organisms, 44 freshwater fish, 43 mammal, 23 bird and 15
amphibian species. According to Prof. Melodie McGeoch, lead author on the
publication and member of the Centre for Invasion Biology, these numbers are a
significant underestimate. “We showed that regions with low development status
and little investment in research have lower than expected numbers of invasive
aliens”. An increase in the number and spread of alien species, which adversely
affect the habitats they invade, is nonetheless attributed to a substantial rise
in international trade over the past 25 years.
“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,” says Dr Stuart Butchart from BirdLife International.
“This shows that although we are winning some battles in the fight against
invasive species, current evidence suggests that we are losing the war.”
If left uncontrolled, invasive alien species can have a serious impact on
native species. The Yellowhead, a bird endemic to New Zealand, has suffered
considerably in recent years due to a surge in the number of rats. Two
populations of the Yellowhead are now extinct and three more are significantly
falling in number, leading to the species to move up from Vulnerable to
Endangered on the IUCN Red List of Threatened Species™.
Similarly, the pathogenic chytrid fungus, which was entirely unknown until
1998, is thought to be the cause of the decline and extinction of many amphibian
populations around the globe. The disease, caused by the fungus, can be spread
by humans and a host of other species, ranging from exotic fish to African
Clawed Frogs.
But the impact of invasive alien species can be successfully controlled. The
Black-vented Shearwater, a seabird native to Natividad Island off the Pacific
coast of Mexico, was under threat from cats, goats and sheep. But since they’ve
been eradicated, the status of the bird has been reduced from Vulnerable to Near
Threatened on the IUCN Red List. Similarly, the control of the Red Fox in
south-western Australia in the last decade allowed the population of the endemic
Western Brush Wallaby to recover sufficiently for it to be downlisted on the
IUCN Red List to Least Concern.
“It’s likely to be more cost effective to prevent the spread of invasive species in the first place than to tackle the biodiversity crisis once they have become established,” says Dr Bill Jackson, IUCN’s Deputy Director General and Chairman of GISP. “With sufficient funds and political will, invasive species can be controlled or eradicated. This will allow native species to be saved from extinction, but countries need to dramatically improve the way they deal with the problem.” - IUCN
More information:
The publication was produced by scientists from the Centre for Invasion
Biology (Stellenbosch University), BirdLife International and IUCN.
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