Ecological Interlopers – Understanding Invasive Species

Second to habitat loss, invasive species pose the greatest threat to biodiversity. Invasives crowd out native plants and fish. They take over our woodlands, our wetlands and our waters. And because they’re survivors, they are both difficult and costly to get rid of.

Invasive Species Resources

But wait a minute… let’s start from the beginning. What are invasive species and why should we be concerned?

Even the word invasive spells trouble. The root of Invasive comes from the word invade… and that’s exactly what they do. Invasive species—introduced or alien species as they’re often called—are non-native species that invade and disrupt the ecosystems they colonize. They pose a threat to biodiversity by outpacing native species either by growing and spreading at alarming rates or by outcompeting habitats and food sources.

Toronto and Region Conservation (TRCA) staff monitor many different types of invasive species, including terrestrial or plant species, aquatic or water based species and insects. And all present their own unique problems and challenges.

The entry of invasive species to North America dates back hundreds of years, when crops from other countries were brought here to be grown as food sources. Later, cargo ships brought invasive species with them in ballast tanks. Seeds arrived in shipments of food and even plants, used as decoration in gardens became problems as they made their way out of backyards and into our forests. Invasive species continue to survive and thrive because they can reproduce at a more rapid rate, have few natural predators and can adapt to different habitats.

Ontario, and the GTA in particular, are home to a number of invasive species. You may unwittingly have some of them in your own backyard or see them when out enjoying a day out on the water.

Terrestrial invasive species that pose problems in our region include dog strangling vine, garlic mustard, giant hogweed, phragmites and Japanese knotweed.

These are determined plants, with intricate root systems that allow for rapid spread across ecosystems. Simply pulling them up often makes the problem worse. For example, if garlic mustard goes unchecked, it can decimate entire plantations of Ontario’s provincial flower, the beloved trillium. If you try to pull it out, the plant senses it’s under attack and sends out an emergency response – a kind of chemical reaction that keeps enough residual plant material in the ground to allow the plant to survive.

Some plants can even be dangerous. If the sap from giant hogweed gets on your skin then is exposed to sunlight, serious burns can occur.

Aquatic, or water-based invasive species can be found in lakes and rivers in our area. The ones that are posing serious concerns are Asian carp, round goby, zebra mussels and sea lamprey.

Aquatic invasives reproduce quickly and can adapt in habitats and conditions not usually conducive to survival. Asian carp and the round goby are voracious eaters too and can literally clear out the food sources and habitats of native fish like trout, salmon or other fish native to our region. Sea lampreys are parasitic, meaning they attach themselves to fish and feed on their internal fluids, eventually killing the host fish. Zebra mussels filter plankton out of the water, depleting it as a food source for other fish and often cluster in vast numbers on the bottom of water craft.

Not only do invasive species threaten our forests, wetlands and waters, they also cost our economy. It’s been estimated the annual financial impact of invasive species across all sectors—the forests, agriculture and those found in the Great Lakes—is nearly $30 million dollars. Prevention remains the most important work to be done, and that’s why we all need to work together to become aware and vigilant against the spread of invasive species. TRCA will continue to work with our partners to help protect our natural world.

For more information and tips on how to deal with invasive species, see Ontario’s Invading Species Awareness Program and Invasive Species in Ontario.