Alien Species in British Columbia

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
hybridization.

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 have arrived.

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 agencies.

NEW! Invasive Alien Species Framework for BC: Identifying and Addressing Threats to Biodiversity

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.