Some have been introduced intentionally for use in
agriculture, forestry etc, and others as the accidental result of human
activity, e.g. in ships’ ballast water or via the transport of goods. This is a
global issue. In Britain alone, there are over 3,000 non-native species. Many
non-native species are harmless, causing no disruption to the environment or
native wildlife in their new locations, but occasionally a species will
establish and thrive in a way that can pose a threat to native biodiversity.
These species are referred to as invasive non-natives.
How are they spreading?
A huge number of living species – perhaps as much
as half of global biodiversity – owe their existence to the separation of
regions of the world by physical barriers that stop different ecosystems and
ecological communities from mixing. These barriers are the oceans, mountain
ranges, deserts, rain-shadows and currents. They have forced evolution to
operate independently in different parts of the world, producing diverse and
regionally characteristic floras and faunas – giving us, for example, tigers as
forest cats in Asia, but jaguars as forest cats in South America.
People, however, have a long history of moving
animals and plants around the globe and – either deliberately or inadvertently
– allowing them to establish in new areas. This effectively breaks down these
geographical barriers to species movements. Free from native predators,
pathogens and competitors, the new non-native arrivals often flourish and
sometimes create severe problems for native wildlife.
What’s the problem?
The introduction of invasive non-native species is
the second biggest threat to global biodiversity after habitat loss. Islands
and freshwater habitats are particularly vulnerable, and bird species across
the world have experienced severe impacts: invasive non-native species have
been involved in the extinction of 68 out of the 135 bird species lost in the
wild globally over the last 500 years.
Even moving species outside their range within the
same country can cause problems. There are several examples where mammals
native to one part of a country have been introduced to offshore islands where
they do not occur naturally and have caused problems for biodiversity.
Invasive non-native species can cause problems for
native wildlife in several ways:
·
Predation - introducing
new predators into an area can have devastating effects on the native wildlife
and ecosystems. Biodiversity on islands and lakes is extremely susceptible to
introduced predators, as native species have often evolved in the absence of
predators and are not able to adapt quickly enough when they are introduced.
·
Competition for resources - introduced
species can out-compete native wildlife for resources like food, breeding
sites, space etc. Japanese knotweed, an introduced plant to the UK, forms dense
stands that can prevent native plants from growing. This can change the habitat
structure of an area, making it unsuitable for the other organisms that live
there.
·
Introducing new diseases - introducing
new diseases can have serious consequences, as native species will not have
developed immunity. Signal crayfish, an introduced species to the UK, is a
carrier and host of the crayfish plague, which can kill our native crayfish.
·
Hybridisation - some species
are capable of breeding with another related but distinct species, creating
hybrids. Over time, the unique genetic diversity of one species can be lost and
the species can become extinct. See our page on white-headed ducks and ruddy
ducks.
Invasive non-native species are not just a threat
to biodiversity; they can also damage economic interests such as agriculture,
forestry and fisheries. The cost of dealing with invasive non-natives in
Britain is estimated to be several billion pounds annually.
What can be done?
It can be hard to identify which non-native species
are likely to cause a problem. It may appear that the introduction of a new
species is harmless, only for problems to arise once the species has become
established. There are concerns that climate change may make it easier for
non-native species to become established in new areas as environmental
conditions change.
Preventing invasive non-native species from being
introduced in the first place, or, if that fails, acting quickly to prevent
them becoming established, are key to tackling this issue. In places where
invasive non-natives are already present and considered a threat, control or
eradication of the population may be considered. There have been notable
successes, especially on islands, where removing invasive non-native species
has enabled the recovery of native wildlife populations.
The RSPB has been closely involved with
constructing policy and legislation on non-native species issues, both
nationally and internationally. We do not advocate the ‘demonisation’ of
non-native species, or the eradication of every plant or animal brought to the
UK by people; some non-native species do not have a direct detectable effect on
native wildlife, and some species are too well established for any realistic
practical response. However, where native wildlife is threatened, and where a
practical response is possible, we do promote effective and humane measures to
protect native species and habitats from damage or extinction.
We will continue to help develop and implement the
government’s Invasive Non-native Species Framework Strategy for Great Britain,
and we are pressing for effective EU legislation on non-native species.
Currently national legislation is patchy and inconsistent across the EU, and we
need to bring all Member States to a minimum standard in this regard: if any
one country allows the preventable establishment of damaging non-native
species, wildlife across the whole European Community is then put at risk.
