THE ISSUE
The vast majority of ecosystems on Earth are currently occupied by foreign, human-introduced species. These invasive species are introduced to a new environment (most often from human activity), establish themselves, and have negative impacts to local ecosystems.
Invasive alien species can have a negative impact on biodiversity by:
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Displacing native species
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Competing with native species for resources
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Altering and degrading habitats
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Introducing new diseases
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Impacting reproduction by breeding with native species
Invasive animal species can cause extinctions of local species through competition, predation, and habitat alteration. Their impact on native ecosystems, habitats, and species is severe and often irreversible.
The Cause
As the world grew more connected through global travel and commerce, humans began introducing countless non-native species to new ecosystems.
The Canadian government cites numerous factors responsible for the introduction and spread of alien species, including:
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Climate change
In many cases climate change may create new environmental conditions that are favourable for the invasion and establishment of new species into the ecosystem. For example, in the boreal forest of Alberta and Saskatchewan, recent research has shown that the northern movement of white-tailed deer is driven primarily by the warming climate and a decrease in winter severity. Historically, white-tailed deer didn’t occupy the boreal forest, and their recent arrival has been linked to declines in populations of endangered boreal caribou populations.
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Intentional introductions
Many invasive species were historically introduced to North America for their ornamental or aesthetic value. European Buckthorn is a vastly widespread shrub that outcompetes native plants across Eastern Canada. It was originally introduced as a shrub used in gardens and along fence rows.
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Increased susceptibility of altered or degraded ecosystems
As ecological generalists, invasive species are often tolerant, and even thrive in challenging environment conditions. As superior competitors, they often push out native species that are specifically adapted to healthy local ecosystems. For example, the Eastern Barred Owl has thrived in urban areas across Western Canada, while the native Spotted Owl (old-growth specialist) is critically endangered in Canada.
The Impact
The feral wild boar is an invasive species whose population is growing exponentially in Canada, especially in the Prairie provinces. Considered to be the most damaging invasive species in the United States, wild boar spreads harmful diseases and destroys valuable grassland, wetland, and forest habitats. They also prey upon sensitive birds, small mammals, and invertebrates. Like most invasive species, wild boars reproduce quickly, are highly adaptable, and are extremely difficult to remove from a landscape once they have established populations. Researchers predict that eradication in Canada is no longer possible, and that wild boar may soon outnumber people in the province of Saskatchewan.
Invasive plant species may also outcompete local species and can dramatically change the way in which nutrients are cycled throughout ecological systems. For example, Japanese Knotweed is an extremely aggressive invasive, bamboo-like shrub that is found throughout Canada. Research has found that knotweed is capable of displacing the majority of native plant species, especially in wetland areas. These plants are able to adjust the local soil chemistry to favour their long-term success and their strong roots even threaten to damage human infrastructure such as foundations.
Similar to the Japanese Knotweed is English Holly. This evergreen changes the soil by concentrating it with sulfur, growing beyond the height of natives, and invading below with deep and thick root systems. Once the canopy has been burned or taken down, an environment full of holly outcompetes all native shrubs, and prevents new tree seedlings, like those of Douglas Fir, from growing. In this way, the structure of a forest can be dramatically altered and has far-reaching impacts. Moreover, these invasions are much more likely given the hundreds of wildfires experienced on a yearly basis in the Pacific Northwest.
Scotch broom is another example of a shrub that has had significant impact on the Pacific Northwest coastal ecosystems, particularly that of Garry Oak savannas. It renders its occupied soil more acidic and can decrease the amount of phosphorus content. Consequently, excess nutrients can invite additional foreign species to thrive, decreasing the opportunity for native vegetation and reducing the habitats of local pollinators . This plant also creates stems that can act as kindling, helping a fire spread rapidly. As thousands of seeds can spread each year from one single plant, it is critical to remove this species as soon as it’s found. Studies show that if communities do not act quickly, removal becomes less and less effective over time.
European wall lizards are found to be high risk in British Columbia, competing with the Northern Alligator Lizard, the Pacific chorus frog and the endangered Sharp-Tailed Snake for space and sustenance. Like many other invasives, they also decrease native pollinator numbers.
While we may not think of them as invasive, domestic and feral cats have a tremendous impact on local bird populations. A bird mortality study found that over 95% of cases were due to collisions with human-made objects and attacks by cats. The numbers are staggering, with over 100 million birds being killed by cats each year in Canada alone. Felines have been found to also be a threat for other native species like butterflies and moths.
Solutions
Invasive species tend to reproduce quickly and be highly resilient to removal efforts once they have been established. Therefore, the prevention of alien species introduction remains a critical step in maintaining local biodiversity. Countless local Canadian invasive species societies advocate for invasive species introduction prevention through principles such as “clean, drain, dry” that attempts to educate local communities to help stop the spread of invasive aquatic species by personal watercraft. Promising research has also shown that community science platforms like iNaturalist can also be used in the early detection of invasive species to target early management actions.
Once invasive species are established in a particular location, complete removal of the invader is often very difficult, may cause pollution (such as in the case of herbicides), or may even create difficult or undesirable ethical outcomes where one species may be killed to save another.
While Barred Owls are native to eastern North America, their range has expanded west, likely because of human disturbance and development. In their new western habitat, Barred Owls are prolific hunters which outcompete local Northern Spotted Owls. In response, thousands of Barred Owls have been killed throughout North America in an effort to restore populations of Northern Spotted Owls. Over the next thirty years, the U.S. plans to kill nearly half a million Barred Owls in efforts to save Spotted Owls. Ultimately, adequate habitat protection over the past century may have prevented the spread of Barred Owls in the first place. Protected areas are less likely to contain invasive species. Taking together prevention, early detection, targeted management, and habitat protection present the best solutions to invasive species management.
