Trends in invasive alien species
Alien species are animals, plants and micro-organisms that spread or are introduced to areas beyond their natural geographic range due to human activities. Alien species may be introduced to new areas deliberately or unintentionally through activities such as cargo shipping. Alien species are considered to be “invasive” when they present a risk of harm to the environment, economy and/or human health of the new areas that they inhabit.
Invasive species are one of the primary threats to biodiversity. It is estimated that invasive species contributed to nearly 40 per cent of all animal extinctions for which the cause is known since the 17th century. Invasive species may exert negative impacts on an ecosystem by:
- competing for food, water, space, and other resources;
- altering the habitat; preying directly on or parasitizing native species;
- weakening the gene pool by interbreeding with native species; and
- spreading disease (in fact, an invasive species may be a disease itself).
MNR has recognized that “[p]reventing the introduction of invasive species is the key to avoiding long-term harm to our ecosystems.”
In Ontario, the Great Lakes Basin has been the area most affected by invasive species, with over 180 species introduced into the Great Lakes alone, some of which are considered invasive. Invasive shellfish species such as the prolific zebra mussel are believed to have been transported to the Great Lakes in the ballast water of large ships. The sea lamprey, a parasitic eel-like fish that causes devastating ecologic damage, is believed to have spread to the Great Lakes through the man-made canal system. In terrestrial biomes, MNR reports almost a quarter of all Ontario’s plant species are alien. Invasive species have been identified as “a main direct driver of biodiversity loss across the globe.” Current trends suggest that that the rate and risk of introduction of invasive species have increased signifcantly in recent years. Invasive species are an indicator for assessing progress towards the 2010 Biodiversity Target.
This is an article from the 2007/08 Annual Report to the Legislature from the Environmental Commissioner of Ontario. Click here for more information on the official document and its release.
