Alien Species in British Columbia

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 "invasive" species.

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 or diseases;
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, mountains 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 35 years.

Between 1851 and 1960, a new species became established in the bay and estuary every 55 weeks.
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.