species that fit into this category of risk. Endangered means the species is close to becoming extinct or extirpated. There are 238 endangered Canadian species, including the barn owl, northern cricket frog, and the swift fox. Threatened species are those at risk of becoming endangered if some form of intervention doesn’t take place. There are 146 threatened species, including the wood bison and humpback whale. Special concern refers to species that are beginning to show some signs that populations are decreasing to the point where they may become threatened. There are 157 Canadian species at this level of risk. Some examples are the polar bear, Atlantic cod, and the red-headed woodpecker. Canadians must act now to protect species already placed on one of these levels of risk and to ensure no others are placed at risk. There are many possible causes for population declines in Canadian species. Some of the main causes are loss of habitat, pollution, and climate change. Much of the loss of habitat can be attributed to urban expansion. Urban expansion occurs when new homes and buildings are constructed in areas that were previously wild. This takes away habitat and food for wildlife and can place species at risk. You have already learned that natural resources such as forestry, fossil fuels, and mining can also destroy habitat. Natural resources companies claim that they will return the habitat to its original condition when they are done. This sounds good, but it might be too late for some of the species. Destroying the habitat could place a species at risk. If that species becomes extinct, it won’t help that the company returns the vegetation afterwards. The species is gone and the damage cannot be repaired. This is why careful study of a region must be completed before a company is allowed into an area. That’s also why some regions must be protected from mining or logging. If a species at risk is in the area and a forestry company starts clear-cutting, they could wipe out the species completely. Climate change and pollution make matters even worse. Changes in temperature often cause species to die off rapidly before anything can be done to help. Pollution in the environment can poison a species, and often the weakest organisms, such as the young, die first. Think of an ecosystem as being like a large house of cards. The cards at the bottom hold up the other cards above them. If there are lots of cards in the house, the structure is stable and unlikely to collapse. Removing a single card is like having a single species in an ecosystem become extinct: it won’t make the whole structure collapse. You might even be able to remove several cards and the house Copyright © 2010 The Ontario Educational Communications Authority. All rights reserved. ilc.org
Lesson 14 Environmental Science SVN3E-A 16 will stay standing. Removing several cards from the house of cards is like several species becoming extinct, which has happened in Canada. Eventually, when enough cards have been removed, the entire house collapses. The same is true of an ecosystem. If enough species go extinct, biodiversity will drop dangerously
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