An Introduction to Endangered Species in Canada

Today, May 21, 2021, is designated as Endangered Species Day, so we have established this article as the first in a series on the subject of endangered species in Canada, and in the Province of Ontario. This article includes a number of important definitions, an explanation of how species become endangered, and a brief breakdown of how these species become categorized as such.


Before delving into this article, this section will provide a few definitions for your understanding. This subject includes a significant amount of technical jargon, and as such we want to ensure your understanding of all terms.

Species at Risk: A species at risk refers to the danger of extinction or disappearance of a plant or animal species. Most of these species face problems that are exacerbated by human activity. These species are considered “at risk” when they become fewer and fewer in number by scientists. As well, scientists and various levels of government use terms such as “special concern” “threatened” or “endangered” to describe the category that best fits the condition of each species and their numbers across the province and country.

Environment Canada established Figure 1 in an effort to easily illustrate the differences between the various terminology that is usually associated with species that are considered “at risk”. As illustrated, a species categorized as “endangered” is one that is facing imminent extirpation or extinction. While these species still have a chance of making a comeback before extirpation or extinction occurs, it is unlikely without positive human intervention.

Figure 1 – Environment Canada Species Definitions

Before we continue, it is important to understand that the habitat of an endangered species is critical to its health and survival. Just like people, animals and plants require certain environments and conditions to thrive. As such, there is a common term that is used when discussing endangered species, and that is “significant habitat.” According to an important piece of legislation, the Provincial Policy Statement (PPS), when referring to endangered species, the definition requires the exhibition of two basic characteristics:

  1. Necessary for maintenance, survival and/or recovery of naturally occurring or reintroduced populations; and
  2. Occupied or habitually occupied by the species during all or any part(s) of its life cycle.

While the species may only use the habitat for portions of the year (e.g., certain seasons, reproduction), it would still be considered significant. What does this mean? Well, when a habitat is categorized as significant, there will be certain government protections on that habitat and its surrounding features to avoid negative human interference.

Genetic Variation: Refers to the difference in DNA among species or the differences between their populations. There are multiple sources of genetic variation, including mutation and genetic recombination.

Now that we have gotten some important terminology out of the way, we are going to discuss some of the main reasons why species become endangered.

How Does A Species Become Endangered?

More often than not, a species will become endangered for 2 main reasons: loss of habitat and loss of genetic variation. Loss of habitat and loss of genetic variation can occur both naturally and by means of human intervention.

Loss of Habitat

Figures 2-3 – Forest fire, Tornado, Oil Spills

A loss of habitat can happen naturally. For instance, a forest fire or natural disaster could occur, altering the ecosystem and its elements. The impact of this could be a loss of shelter or food source, making the habitat no longer ideal or possibly inhabitable for the species. Again, like humans, many plants and animals require specific conditions to survive and grow. If these conditions cannot be met, then the species will be forced to relocate and/or adapt, or face the consequences and become more vulnerable.

Alternatively, human activities are common contributors to the loss of habitat. Development and its related activities can either directly or indirectly endanger species. For instance, development eliminates habitat and native species directly when forests are cleared. To “clear” a piece of land is to remove all trees and vegetation from it, completely altering the landscape and the patterns of the countless species that rely on it and one another to survive. However, development can also indirectly endanger species. Some species, such as fig trees, may provide habitat for other species. As these trees are cut down, the species that depend on that tree for shelter may also become endangered.

Loss of habitat can also occur as development takes place within a species’ geographic range. Many animals have a range of hundreds of square kilometres, but as urban areas continue to grow and expand into the wilderness via urban sprawl, the species’ range becomes smaller. This results in the habitat being able to support fewer members of the species population and can lead to increased encounters between wild species and humans. As development brings people deeper into a species’ geographic range, they may have more exposure and more frequent interactions with such species. For instance, poisonous plants or fungi might grow closer to homes or educational institutions, or wild animals will be spotted in backyards or on residential streets. These animals are simply patrolling their range, but some of these species are predators brought closer to people as they lose their habitat to homes, farms, and businesses. More often than not, this results in people killing these animals through pesticide use, accidents such as car collisions, or hunting, which can cause these native species to become endangered.

Loss of Genetic Variation

Figure 5 – Understanding Genetic Variation

Genetic variation is the diversity found within a species. It is why for humans, some families have predispositions to certain mental or physical illnesses or share certain traits such as hair colour. Genetic variation allows species to adapt to changes occurring within their environment. Generally speaking, the greater the population of a species, the greater its genetic variation.

The loss of genetic variation can occur both naturally or via human intervention. For instance, certain groups of species have a tendency to inbreed (reproduce with close family members). These species tend to have little genetic variation because no new genetic information is being introduced to the group. This makes the disease much more common and much more deadly, as inbred species do not have the genetic variation required to develop necessary resistance. For these reasons, fewer offspring of inbred species tend to survive to maturity (illustrated in Figure 5).

Human intervention can also lead to a loss of genetic variation through activities such as overhunting and overfishing, as they can result in the reduction of species populations. Human intervention relating to breeding activities can impact genetic variation as well. Ideally, breeders will pair up two mature members of a species that are not closely related and can produce healthy offspring. However, with fewer breeding pairs, genetic variation tends to shrink. For example, ideal breeding pairs have become less common with dog breeders over the years, making certain breeds more susceptible to physical or health issues.

When it comes to plants, monoculture (the agricultural method of growing a single crop) can also reduce genetic variation for similar reasons to the inbreeding of animal species. To avoid issues, plant breeders can go back to wild varieties in order to collect genes helpful for cultivating plants that are able to resist pests, drought, and/or adapt to climate change. However, due to climate change, wild varieties are also threatened; meaning domesticated plants could lose an important source of genetic traits that could help them overcome new threats.

Identification of Endangered Species

a man holding a magnifying glass
Figure 6 – Magnifying Glass

While we are going to be diving deeper into the government’s role in defining and protecting endangered species in our follow-up article focusing on legislation and government, this section includes a basic breakdown of the core criteria that must be met for a species to be defined as endangered, and who defines them.

In 2002, the Government of Canada passed the Species at Risk Act, the first act targeting endangered species. Under this legislation, the Committee on the Status of Endangered Wildlife in Canada (COSWEIC) has the authority to determine which species are categorized as “at risk”. COSEWIC is funded by Environment Canada but otherwise operates independently of the government, commissioning studies of native species whose survival in the country may be at risk. Based on that research, species are then placed into one of the categories illustrated in Figure 1; extinct, extirpated, endangered, threatened, or special concern.

Some of the core criteria that must be met in order for a species to be defined as endangered, include:

  1. Population Reduction Rate – A species is classified as endangered when its population has declined between 50 and 70%. This decline is measured over a decade or three generations of the species – whichever is longer. The species can be classified as endangered whether or not the cause of the decline is known.
  2. Geographic Range – An endangered species’ extent of occurrence (or entire geographic range they travel and inhabit) is less than 5,000 km2, while their area of occupancy (the area in which they inhabit) is less than 500km2.
  3. Population Size – A species is classified as endangered when there are fewer than 2,500 mature individuals. When a species population declines by at least 20% within 2-5 generations, it may also be classified as endangered.
  4. Population Restrictions – A species is classified as endangered when its population is restricted to less than 250 mature individuals. When a species’ population is this low, its area of occupancy is not considered.
  5. Probability of Extinction – The probability of extinction in the wild is at least 20% within 20 years or 5 generations – whichever is longer.


Plants and animals face many obstacles in their lives. Normally these obstacles include elements such as predators, disease, access to food and water, adequate shelter, and avoidance of natural or man-made disasters. Unfortunately, humans are significant contributors to the obstacles and hardships experienced by ecosystems and the species that inhabit them. With activities such as farming, clear-cutting, and development, humans take away the habitats needed for survival by destroying entire ecosystems so we can alter the land for our purposes. This makes it incredibly difficult for at-risk species to recover without human interference.

Keep an eye out for the next part in this series, which will be focusing on the role the federal and provincial governments play in the protection and recovery of endangered species.

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