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29.2: Menaces pour la biodiversité

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Threats to Biodiversity

29.2: Threats to Biodiversity

There have been five major extinction events throughout geological history, resulting in the elimination of biodiversity, followed by a rebound of species that adapted to the new conditions. In the current geological epoch, the Holocene, there is a sixth extinction event in progress. This mass extinction has been attributed to human activities and is thus provisionally called the Anthropocene. In 2019 the human population reached 7.7 billion people and is projected to comprise 10 billion by 2060. Indicative of our impact, by biomass (the actual mass of a particular species), humans make up 36% of Earth’s mammals, livestock 60%, and wild mammals only 4%. Approximately 70% of all birds are poultry, so only 30% are wild.

To minimize human impact on biodiversity and climate, we have to understand which of our activities are problematic and balance the needs of human civilization and progress with a sustainable plan for future generations. Some of the major threats to biodiversity include habitat loss due to human development, over-farming, and increased carbon dioxide emissions from factories and vehicles.

Case Studies

A case study in human impact on the weather can be found in the 1930s event known as the Dust Bowl. In the 1920s and 30s, a large number of farmers moved to the Great Plains and clear cut the land, removing the native ground covering plants in order to plant their crop plants, which generally have shallow root systems. In an area centered in Kansas and northern Texas and extending north into Canada and south through Texas, a combination of extreme drought conditions and poorly considered farming practices resulted in dust storms that deposited debris all the way to the northeastern states. Ultimately, because of these storms, and the depressed economy that unfortunately coincided, there was a general food shortage and many families had to abandon their farms. It has become clear that in order for the land to support single plant species which are not naturally adapted, farms must be well planned to account for the loss of biodiversity.

A less radical example can be seen in Yellowstone National Park in the United States. Wolf populations diminished radically after the westward migration of the human population began. As a result, the population of prey animals such as the pronghorn and mule deer increased. Because those animals tend to eat young Aspen saplings, this resulted in a decline in Aspen trees. The downstream effects of this loss of trees include increased land erosion and a loss of habitat for birds and other animals. Support for this proposed chain of events comes from the recent reintroduction of wolves to Yellowstone, which correlates with an observed rebound in the Aspen population in the park. If this correlation truly indicates that the Aspen is revitalized due to the reintroduction of wolves, this research bolsters the general concept that apex (top) predators are essential to the biodiversity of ecosystems.

Maintenance of biodiversity is essential to preserve ecosystems in balance, prolong predictable weather patterns and to keep raw material for research into new industrial and medical products.

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