How do invasive species travel?

Definition: Invasive species pathways are the means by which these species are moved from one location to another.

There are natural pathways, which include wind and water currents. However, there are also other pathways which are either created by or made more accessible to these species by human activity. Sometimes humans create these pathways intentionally, other times quite unintentionally.

Here is an example of what can happen...

A family takes their motor boat out to First Lake one afternoon. While out on the lake, several zebra mussels attached themselves to the underside of the boat. At the end of the day, the family loads their boat onto their trailer, and drives away with their boat and the hitchhiking zebra mussels! The following day they decided to visit another lake in the region, Second Lake. They brought their boat and hitchhikers with them. Once the boat was in the water, the hitchhikers left the boat and were introduced to Second Lake.

What was the spotted knapweed pathway?

Spotted knapweed was introduced to North America from Europe via soil that was used as ship ballast, and as a contaminant in alfalfa seed. This happened in around the year 1900.

Definition: Ballast describes anything that is used as a weight to stabilise a boat.

Ship ballast

Shipping vessel discharging ballast

Many cargo boats use water as ballast. When they aren't carrying any cargo, they need to add weight to the ship to ensure that the ship will remain upright. When they want to load the cargo, they discard the ballast and load the cargo. Many invasive species are introduced through this pathway.

Once the spotted knapweed was introduced, it spread throughout the continent in domestic alfalfa seeds, in hay, on the undersides of vehicles, and through rivers or waterways before being recognized as a serious threat to native plants, wildlife, and livestock. Now spotted knapweed can be found in many provinces, the Yukon, and throughout the United States.