What are Alien Species?
Alien species are plants, animals and
microorganisms from one part of the world that are
transported beyond their natural range and become established
in a new area. They are sometimes also called "exotic,"
"introduced," "non-native," "non-indigenous" or
Species that are considered aliens in
this province may come from outside British Columbia
or be native to some parts of British Columbia, but
are counted as aliens in regions of the province where
they have been introduced.
Not all species that arrive in new places
are able to make themselves at home and start reproducing
and spreading. However, alien species can get established
if given advantages such as:
- an agreeable climate;
- no or few natural predators, parasites
- an abundance of food plants or prey that
lack protection against the newcomer; and
- an ability to out-compete native species
and corner the best resources.
How Do They Get Here?
The natural range of a species is defined
by physical barriers that prevent dispersal, usually
inhospitable habitats where the species is unable to
survive. Humans have created many opportunities for
plants, animals and microorganisms to spread beyond
their natural ranges - carrying them across oceans,
and deserts, and transferring them from one water body
to another. In some cases, this has been deliberate,
though often with unexpected consequences, while in
other cases it is unplanned.
Why Should We Be Concerned?
Most non-native species that make their
way to British Columbia are either beneficial or relatively
harmless, and only a small percentage of these species
will be able to survive independently - fewer still
will be detrimental. However, all alien species must
be treated with caution, because it is difficult to
predict which ones will cause problems over time. Even
those that have been harmless in the past could become
troublesome if conditions change to conditions that
are more hospitable and encourage reproduction and
expansion (e.g., because of global climate change).
There is cause for concern because the
rate of alien species introduction is accelerating
rapidly as global commerce and travel increase. In
San Francisco Bay, for example, roughly half of the
alien species now living there arrived in the past
- Between 1851 and 1960, a new species
became established in the bay and estuary every
- Between 1961 and 1995, the rate of establishment
was one new species every 14 weeks.
Even though harmful aliens are a minority
of all non-native species, the damage they do can be
severe and wide ranging.
The negative consequences of alien species
introduction can be roughly divided into economic costs,
human health risks and ecological consequences, categories
which frequently overlap.
What Are the Economic Costs?
Alien species can have significant economic impacts because many aspects of our human economy rely on services and
functions provided by nature. Natural resource-based sectors most affected by alien species include:
- fisheries and aquaculture; and
- tourism and outdoor recreation.
There are also financial costs incurred when alien species damage infrastructure.
Most intentional introductions of aliens are based on economic motivations, yet they are seldom preceded by a
careful cost-benefit analysis that includes societal and ecological consequences. It is rarely those responsible for introducing
an alien species, either intentionally or accidentally, who pay for resulting damages. Instead, consumers, other resource users
and tax-payers bear most of the burden.
The Canadian Food Inspection Agency classifies 94 alien species as agricultural or forest pests and estimates
that these regulated species cost the Canadian economy $7.5 billion annually. That figure does not include costs that arise from
regulated pests on natural ecosystems or the impacts of unregulated alien species. In the United States, the total cost of
preventative measures, control programs and lost production due to alien species is estimated to exceed $137 billion a year.
What Are the Human Health Risks?
Public health issues are rarely discussed from the perspective of alien species, even though the spread of pathogens
has had a profound effect on human health, both historically and in modern times. When European explorers set off for the "New World"
they carried invisible but lethal baggage with them. Following the arrival of Columbus, 95% of the indigenous population died from
smallpox, measles, whooping cough, influenza and other imported diseases, which were completely new to them.
West Nile virus is one of the most recent alien diseases to reach North America. After first appearing in New York
City in 1999, it quickly spread across North America, reaching Ontario by 2001. Statistics on the effects of this virus on humans and
animals are dramatically changing on a seasonal and annual basis.
Bacteria, viruses, protozoan and other microbes can travel with us in and on our own bodies, or via transported
food, livestock, wildlife, or goods, and are also amongst the many aliens carried in ballast water. Another entry point for alien
pathogens is the exotic pet trade - a growing concern as both the number of people purchasing these animals and the number of different species being imported is increasing. These organisms may have minor to severe effects on humans, domestic and wild animals.
What Are the Ecological Consequences?
Alien species are the second greatest threat to biodiversity, after habitat loss and degradation. When alien species move in, native species' populations often decrease in parts of their natural range or, in the worst-case scenario, the native species
become extinct. The number of plant and animal species may remain the same in an area as common or widespread species replace unique, local species, but the integrity and vitality of natural ecosystems is damaged.
Alien species affect native species through:
- competition for limited resources (including space, light, moisture, food, breeding sites and pollinators);
- predation, grazing and browsing pressure;
- introduction of diseases and parasites; and
Species at Risk
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) estimates that 25% of endangered species; 31%
of threatened species; and 16% of Special Concern species are negatively affected by alien species.
Predation, Grazing and Browsing
The impact of alien predators and herbivores can be devastating to native species that have not evolved appropriate
defences. In the absence of a natural predator-prey balance developed over thousands of years, aliens may simply consume native species until that food source disappears. Besides the obvious negative effect on the target plants and animals, many other native species may
be indirectly affected by the loss or reduction of food sources or habitat.
Introduction of Diseases and Parasites
Alien species do not only pose health risks to humans. Just as alien predators can wreck havoc on prey that lack
protective adaptations, pathogens that are relatively harmless in one place can prove lethal in a new environment.
What is Being Done?
When it comes to alien species, an ounce of prevention is definitely worth a pound of cure.
It is far less expensive to keep unwanted aliens from crossing borders than to try to eradicate or contain them once they
Attempts to combat alien species usually rely on one of three methods:
- physical removal (for example, hand pulling plants or trapping and killing animals);
- chemical control (using herbicides, insecticides, piscicides and other poisons); or
- biological control (with introduced predators or disease organisms).
Each of these can have drawbacks and unwanted side-effects, so control methods must be carefully selected and
monitored. Because of the high reproductive rate of many alien species and the likelihood that a few individuals will always avoid
control efforts, complete eradication of established aliens is usually impossible.
Canada and British Columbia are signatories to a number of international and national protocols, conventions and
policies aimed at preventing intentional and accidental introduction of alien species into new environments.
The Ecosystems Branch of the Ministry of Environment is contributing to a Provincial
Invasive Plant Strategy that is being led by the Fraser Basin Council, in conjunction with stakeholders and other government
Invasive Alien Species Framework for BC: Identifying and Addressing Threats to
The document "Invasive Alien Species Framework
for BC: Identifying and Addressing Threats to Biodiversity" (PDF 1.77MB) is a background document on invasive alien species issues
that affect biodiversity in British Columbia. It sets out a framework for the use of science, and coordinated involvement of partners, to address the threats to BC’s environment and economy posed by invasive alien species.
Invasive alien plants and animals present a growing environmental and economic threat to British Columbia. Conservation biologists
have globally ranked invasive alien species as the second most serious threat to species at risk after habitat destruction.
Collaborative leadership, organization and action are key to addressing invasive alien species concerns in British Columbia. As a
priority, MOE will support coordinated efforts, providing expertise in biodiversity science, policy and standards and other resources as
available and feasible.
Alien Species on the Internet