What are Invaders?
Most people who have heard of invasive species will know that they are one of the greatest threats to the biodiversity of Ontario’s waters, wetlands and woodlands. However, even people who know that invasive species are a problem often have trouble defining exactly what it is that makes a species invasive.
The government of Canada has a national invasive species strategy. That strategy employs the term “alien invasive species” for what is commonly referred to (including on this site) as just invasive species. It defines alien species as “species of plants, animals (including fish), and micro-organisms introduced by human action outside of their natural past or present distribution”. Invasive alien species are defined as “those harmful alien species whose introduction or spread threatens the environment, the economy, or society, including human health.
So an invasive species is one that comes from somewhere else and causes harm in various ways. Many people are surprised to discover that some very familiar plants and animals can be described this way. The common dandelion is so widespread in Ontario and throughout North America that most people take its presence for granted. However, it was introduced here from Eurasia where it is a native species. Large sums of money are spent in efforts to get rid of it from agricultural and urban lands. It is a very successful invasive species.
The rainbow smelt is a common fish species in much of Ontario, where it is caught in both commercial and recreational fisheries. Most people are unaware that it was introduced into the Great Lakes basin in the early 20th Century. It is known to be a significant predator on the eggs and larvae of some native fish species and a competitor with others. It is another very successful invasive species.
There is no public pressure to eliminate these two species from their new ranges. Regardless, there is really no viable way to get rid of either of them. They are managed in various ways, and have become part of the landscape, for better or worse. They serve as good examples of how widespread the problem of invasive species is, how rapidly invasive species can become established and how hard they can be to deal with once they are here.
But the fact that an invasive species is well established does not mean that it no longer causes problems. Consider the common carp. Valued in as a food fish, this species has been deliberately introduced beyond its native range in Asia for many centuries. It was brought to North America by immigrants for the same reason that they brought chickens, cows and wheat; it was a familiar food item that didn’t require learning new skills required to capture and process unfamiliar things. It has become very widely established in North America, where it is now (somewhat ironically) not well regarded as a food fish.
But common carp have proven to be a serious obstacle to efforts to rehabilitate a native species that was once very widely established and important to the economies and cultures of many Anishinabek peoples. Wild rice does not coexist well with common carp, which uproot the plants while feeding and spawning. In area where the carp are established, wild rice can only be reintroduced if barriers are constructed to keep the carp out. This is clearly a case of an invasive species having ongoing effects on economic and social systems long after it has become broadly established. It is much too late to stop common carp from spreading, but it is not too late to learn the lessons it illustrates and put a stop to the next potential invader before it gets here.
Invasive species are introduced and spread through various routes including:
Invasive species can be very difficult, if not impossible, to remove once established. Please help to prevent the introduction and/or spread of invasive species.
You can help: