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10.9: Review

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    After completing this chapter you should be able to...

    • Describe biodiversity as the equilibrium of naturally fluctuating rates of extinction and speciation.
    • Summarize potential causes of mass extinctions and the associated biodiversity loss.
    • Compare the present rate of extinction to the background extinction rate.
    • Describe the causes and consequences of the sixth mass extinction.
    • Describe how the loss of biodiversity is measured.
    • Distinguish among the Red List categories.
    • Name, define, and provide examples of the five major threats to biodiversity.
    • Provide examples of the successes and failures of biological control in regulating invasive species.

    Five mass extinctions with losses of more than 50 percent of extant species are observable in the fossil record. The sixth mass extinction is currently in progress with present-day extinction rates much greater than the background extinction rate.

    The core threats to biodiversity are human population growth and unsustainable resource use. These are habitat loss, overexploitation, pollution, invasive species, and climate change. Habitat loss occurs through deforestation, damming of rivers, and other activities. Water and air pollution introduce toxic substances into the environment that harm plants and animals. Overexploitation is a threat particularly to aquatic species, but the poaching of terrestrial animals and overcollection of plants and fungi also puts species at risk. Invasive species have been the cause of a number of extinctions and are especially damaging to islands and lakes. Climate change is forcing range changes that can lead to extinction. It is also affecting adaptations to the timing of resource availability that negatively affects species in seasonal environments. Climate change will also raise sea levels, eliminating some islands and reducing the area of all others.


    Modified by Melissa Ha from the following sources:

    This page titled 10.9: Review is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Melissa Ha and Rachel Schleiger (ASCCC Open Educational Resources Initiative) .

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