Published : Feb 21,
2013 Last modified : Feb 27, 2013 09:14
AM
Invasive alien species pose greater risks
than previously thought for biodiversity,
human health and economies, according to
two new reports from the European Environment
Agency (EEA).
In many areas, ecosystems
are weakened by pollution, climate change
and fragmentation. Alien species invasions
are a growing pressure on the natural world,
which are extremely difficult to reverse.
Jacqueline McGlade,
EEA Executive Director
An alien or non-native
species is an organism which humans have
introduced –intentionally or accidentally
-outside its previous range. It is deemed
‘invasive’ if it has negative effects on
its surroundings, for example by outcompeting
or predating on native species that have
evolved without specific adaptations to
cope with them. In such cases populations
of native species can be devastated. Evidence
shows that in a growing number of cases
invasive alien species even cause harm to
human health and society.
There are more than
10 000 alien species present in Europe,
and the rate of new introductions has accelerated
and is still increasing. At least 15 % of
these alien species are known to have a
negative ecological or economic impact.
However, non-native species – for example,
some food crops – can also have huge benefits.
The first report, The
impacts of invasive alien species in Europe,
details the effects and spread of some species.
The second report, Invasive alien species
indicators in Europe discusses the methodological
approach in bringing this data together.
The most common reason
species are introduced elsewhere is for
horticulture, while others may be brought
into new areas for other reasons including
farming, hunting, and fishing, or as pets,
the report notes. Transport is not always
intentional – for example, zebra mussels
have stowed away in the ballast water of
ships to proliferate in European lakes.
Increasing trade and
tourism in recent decades may have led to
increasing numbers of alien species. Climate
change may also play a role in the spread
of these species, the report says, making
some areas more favourable to plants and
animals originally from elsewhere.
Jacqueline McGlade,
EEA Executive Director, said: “In many areas,
ecosystems are weakened by pollution, climate
change and fragmentation. Alien species
invasions are a growing pressure on the
natural world, which are extremely difficult
to reverse.”
Invasive alien species
are one of the main threats to biodiversity.
Of the 395 European native species listed
as critically endangered by the IUCN Red
List of Threatened Species, 110 are in danger
because of invasive alien species. The EU
Biodiversity Strategy 2020 has policy targets
which aim to address the problem.
Impacts on human health
For humans, one of the
most dangerous effects of invasive alien
species is as a carrier of disease. The
Asian tiger mosquito has been linked to
more than 20 diseases, including yellow
fever and chikungunya fever. It has come
to Europe mainly through the intercontinental
trade in used tyres, and is now prevalent
in several southern European countries,
especially Italy. Climate change projections
show that the mosquito will likely extend
its range further north in coming years.
Climate change is also
enabling the spread northward of the common
ragweed. The plant is originally from North
America, the seeds first coming to Europe
in mixes of grain intended as bird feed.
It is a powerful trigger of hayfever and
other allergies.
Changing landscapes are another result of
invasive alien species. For example, the
red palm weevil is destroying large numbers
of palms in the Mediterranean region, transforming
the green spaces in cities.
There are also effects
on ecosystems which indirectly affect humans.
In some cases ecosystems altered by invasive
alien species may be less able to provide
important ‘ecosystem services’ which support
human activity. For example, the pollination
carried out by honeybees may be affected
by invasive alien species - the yellow-legged
hornet, native to Asia, has been found to
devastate beehives in France.
Invasive alien species
cost Europe around € 12 billion per year,
according to one estimate. Species such
as the Spanish slug, now found in most European
countries, can devastate crops. Other species
such as the pervasive zebra mussel can also
cause high costs by fouling water filtration
plants and water cooling reservoirs of power
plants.
Invasive species harming biodiversity
Invasive alien species
harm native species through predation, as
is the case of feral cats killing smaller
creatures. Cats have been introduced to
approximately 180 000 islands worldwide,
and have a significant impact - in Britain
alone, cats are estimated to kill 25-29
million birds every year.
The American mink was
originally brought to Europe for fur farming.
Many animals have since escaped or been
intentionally ‘liberated’, so the species
is now common in the wild in many areas
of Europe. It is now outcompeting its European
cousin in many areas, and has had devastating
effects on local wildlife, particularly
ground-nesting birds.
Amphibians around the
world are in decline, in part due to the
invasive chytrid fungus. Other alien species
can spread diseases, as is the case with
the red swamp crayfish, which carries the
‘crayfish plague’. The disease often proves
deadly to European crayfish, as they have
not evolved to cope with the disease.
Hybridisation can also
be a problem. For example, Japanese knotweed
is a particularly virulent hybrid of two
alien species originating from different
parts of Asia, which first came into contact
as alien species in central Europe. The
hybrid has been found to spread faster than
its parents, outcompeting other plants and
altering ecosystems with effects on other
species.
