species are on the edge of extinction, but have you ever wondered why? Explore these major reasons why species become endangered and have to be added to the endangered species list.
Overhunting or overharvesting
There are many historical accounts about how humans have over hunted and over harvested species, leading to their endangerment, and often, extinction. The Passenger Pigeon is a classic example of how humans over hunted a species, leading to the extinction of the entire species.
Plant species can also be overharvested, leading to their endangerment. For example, the Goldenseal plant (Hydrastis canadensis) is a very popular medicinal plant in the United States that has now become threatened due to overharvesting in the wild.
Many species in our world today are becoming endangered due to a loss of their primary habitat. For species that are not able to adapt well to changing conditions, habitat loss is particularly challenging to their survival.
Highly specialized species
In general, highly specialized species that have very specific habitat requirements do not fare well when faced with a changing environment, such as a changing climate, or to a loss in habitat. While some species have become well adapted to human presence, such as the Norway Rat (Rattus norvegicus), some species are so specialized that changes in their environment may threaten their very survival.
Pollution can harm species, sometimes even killing them. When enough members of a species are negatively impacted by pollution, that species may become threatened. For example, the Peregrine Falcon (Falco peregrinus) almost became extinct in Canada when DDT was widely used prior to becoming banned in the U.S. and Canada in 1971.
New species introduction and competition
When exotic species are introduced into a new environment, they are often able to thrive because they do not have any predators there. Because these introduced tend to do so well, they will often outcompete native species that exist within the same niche that they do, and they can become invasive.
One example of this is in the Great Lakes region of the United States, where the Zebra Mussel (Dreissena polymorpha) was accidently introduced, many of the native mussel species in the Great Lakes have now become threatened or endangered due to the presence of the highly competitive Zebra Mussel.
As humans increase in population around the world and move into areas where wildlife live, there is an increase in human-wildlife conflict. Sadly, in many cases, wildlife are often killed when predators kill livestock or eat crops.
For wildlife populations that have already been reduced due to loss of habitat and other issues, such conflicts can increase the chances that a species will become threatened or endangered.
In the United States, the native American Chestnut tree (Castanea dentata) was virtually wiped out due to a chestnut blight fungus that was introduced to the United States in 1904. Because the American Chestnut tree had evolved in conditions without the presence of the blight, it lacked the natural resistance to survive the blight.
Currently, there is ongoing research with the aim of creating a hybrid chestnut variety that is a cross between the American Chestnut and a variety of Chinese chestnut that is resistant to the chestnut blight.
Low birth rate
Some species do not reproduce very often, and they may have few offspring each time that they breed. Other species may take a number of years to become sexually mature, thus reducing their opportunity to breed over their lifetime. In the face of other challenges to a species’ survival such as overhunting or habitat loss, it may be difficult for the species to recover even once the threats have been removed.
High genetic vulnerability
Some species, such as the Cheetah (Acinonyx jubatus), maintain low genetic diversity, which makes them less able to adapt when faced with challenges such as overhunting or habitat loss. This low genetic diversity also makes them more vulnerable to diseases and expressions of negative genetic mutations.
A particular species is rare to begin with
Some species are found only in certain limited areas. If there are only a limited number of individuals of a species that are in existence to begin with, and the environment changes, there is a lower probability that such a species will survive in the future.
Rare species can easily become extinct in the face of hunting. The Sumatran Tiger (Panthera tigris balica) is an example of a rare species that was over hunted to the point of extinction, as there were a very limited number of individuals to begin with.