A look into invasive species 

Stories about invasive species and the environmental and economic damage that they cause can often sound like something from a horror movie, but the danger they pose is very real. An invasive species is one that has been introduced, either by natural means or more commonly by humans, to a location where it is non-native. They are usually widespread and have a negative impact on the local ecosystem. What could sound surprising is that the species itself is not a threat when present in its native habitat; what makes a species invasive is not what it is, but where it is. Here’s a look at some interesting stories about how invasive species spread:

Asian Carps


Asian Carp – Chicago’s She’d Aquarium by Kate Gardiner

Asian carps, as the name suggests, are native to Southeast Asia. They were introduced to the United States for the industrial purpose of keeping retention ponds in wastewater treatment plants clean. They were not intended to be released into the wild, but when these ponds flooded, the fish escaped into the Illinois river system. Asian carp are huge fish compared to native fishes, weighing an average of 40 pounds. They have no known predators in North America and compete directly with native fish for food, eating 20% of their weight per day. Their populations are rapidly growing, causing problems for the natural food web and diminishing native fish species and diversity. Currently, they run the risk of entering the Great Lakes and threatening endangered lake species, unless something is done to stop them. Our best chance to stop their spread is installing barriers upstream of rivers to stop the movement of their offspring.

Cane Toads


Rhinella marinus Cane toad by Brian Gratwicke

Venomous cane toads are a textbook example of biological control gone wrong. They are known for eating almost anything, including various types of insects. They were released in sugar cane plantations in Australia to control the population of the native cane beetles, which were ruining crops. The original 3,000 frogs released ended up spreading to the millions, killing native animals that feed on them by using their venom. What’s even worse is that they did not even end up feeding on the cane beetles that they were intended to help control. This example shows the importance of conducting studies on environmental side effects before releasing any new organisms into the wild.

Why is it that invasive species thrive so well at the expense of other species, when they are a healthy part of their native habitats? The answer lies with co-evolution and limiting factors. In their native habitats, these species have predators and natural challenges that keep their populations at a stable and healthy level. It takes thousands of years for them to co-evolve with other species in the same habitat in order to maintain a predator-prey balance. When removed from their native habitat, they are rid of their natural enemies that they co-evolved with as well as of limiting factors such as cold weather or a lack of food and other resources.

Invasive species can spread by wind and water currents, but also by human facilitated methods. These include getting transported on the sides of ships, in planes, or being deliberately moved by individuals. Raising awareness about invasive species and the damage they can cause could help stop people from bringing plants and animals from abroad for decorative purposes or as pets. Many countries have implemented stricter measures at their borders and airports to stop the spread of invasive species. In fact, some national parks have installed brushes to remove seeds from the shoes of visitors to stop invasive plants from entering.

These are all good preventative measures, but for already infested regions, biological controls can be used. By introducing the invasive species’ natural predator or disease, their populations can be diminished. This method should, however, be used with caution and after studies since the introduction of yet another organism could pose even more problems. They could negatively impact other native species and could become invasive themselves, as with the cane toad example.

Invasive species are a real danger to very delicate ecosystems that take thousands of years to develop. Adding a new organism could tip the balance, especially if its new environment has no predators and favourable conditions for growth. While the environmental and economic damage that they can cause is huge, invasive species are largely preventable, since the main means by which invasive species spread is through humans. It is the responsibility of every citizen to make sure they are not unintentionally bringing potentially harmful species from abroad. It is also the responsibility of governments and organizations to make sure they undertake the proper research before releasing organisms for commercial purposes.

While the examples above have had profound negative effects on the environment, could it be that the most harmful invasive species is actually the one that is spreading them: Homo sapiens?

By Jad Murtada

Please note that opinions expressed are the author’s own. They do not necessarily reflect the views and values of The Blank Page.