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Unit 9: Biodiversity Decline

Buttress roots of a canopy tree in the rainforest of northern Queensland, Australia. Courtesy William Laurance

Buttress roots of a canopy tree in the rainforest of northern Queensland, Australia. Courtesy William Laurance

Unit Overview

Living species on Earth may number anywhere from 5 million to 50 million or more. Although we have yet to identify and describe most of these life forms, we know that many are endangered today by development, pollution, over-harvesting, and other threats. Earth has experienced mass extinctions in the past due to natural causes, but the factors reducing biodiversity today increasingly stem from human activities. In this unit we see how scientists measure biodiversity, how it benefits our species, and what trends might cause Earth's next mass extinction.


Content for This Unit

Online Textbook

  1. Introduction
  2. Defining Biodiversity
  3. Counting Species
  4. Biodiversity Hotspots
  5. Categories of Concern: Critically Endangered, Endangered, Vulnerable
  6. A Sixth Mass Extinction?
  7. Habitat Loss: Causes and Consequences
  8. Invasion by Exotic Species
  9. Other Drivers of Biodiversity Loss
  10. Why Biodiversity Matters
  11. Biodiversity in Your Back Yard
  12. Major Laws and Treaties
  13. Further Reading

Printable Online Text for This Unit (PDF)