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Overview of Extinctions

An in-depth discussion of both historical and modern extinctions, highlighting species-level details, ecological impacts, and implications for biodiversity and ecosystem functioning. Transition towards exploring ecosystem services in future lessons, emphasizing the importance of biodiversity in maintaining these services.

Historical Extinctions

  • Key Concepts:

    • While currently, the Earth is home to more species than ever before in history, it is important to understand that an estimated 99% of all species that have ever existed are now extinct. This highlights the transient nature of life on Earth.

    • Students are encouraged to graph species existence through geological time to visualize the upward trends in species diversity as well as the significant drops associated with mass extinctions.

  • Mass Extinctions:

    • Focus on five major historic mass extinctions:

      • Permian Extinction (around 252 million years ago): Responsible for the loss of over 90% of all marine species and 70% of terrestrial vertebrates, with recovery taking between 50-100 million years.

      • Other notable events include the Late Devonian, Triassic-Jurassic, Cretaceous-Paleogene (K-Pg), and the Holocene extinctions.

Modern Extinctions

  • Recent extinction events have been evaluated from the Pleistocene epoch to the present.

    • Current extinction rates are alarmingly high, with estimates suggesting that between 100 to 10,000 species are going extinct each year, a stark contrast to the natural background extinction rates of only 1 to 10 species per year.

Evidence of Mass Extinction

  • A 2015 comprehensive study by ecologist Gerardo Ceballos indicates that the cumulative extinctions we are experiencing currently surpass normal rates, particularly highlighting a dramatic increase over the last century.

Causes of Extinction

  • The causes behind species extinction are hotly debated, especially concerning the extinction of Pleistocene megafauna, focusing on two major hypotheses: human overkill (intensive hunting by early human populations) vs. climate change and habitat alterations.

  • Examples of Modern Extinctions:

    • Thylacine (Tasmanian Tiger): Extinct due to hunting and habitat destruction.

    • Passenger Pigeon: Once abundant in North America, hunted to extinction in the early 20th century.

    • Lyles Wren: A small bird that faced extinction due to loss of habitat.

    • Golden Toad: Believed to be driven extinct by climate change and habitat loss.

    • Additionally, freshwater species are at higher extinction risk due to pollution, overfishing, and habitat degradation.

Documentation Challenges

  • Tracking species extinctions poses significant challenges, particularly concerning undocumented or lesser-known species. This often leads to an incomplete understanding of the full extent of biodiversity loss.

  • Extinction Debt: This concept illustrates the longer-term extinction risks that may not be immediately evident, suggesting that we may face waves of extinctions in the future due to past habitat destruction and climate changes.

  • Species-Area Relationships: This principle predicts extinction rates based on the size of remaining habitats and the type of ecosystems involved, with case studies illustrating varying impacts on species loss depending on factors like habitat type and resilience.

Conclusion

  • The overarching theme summarizes the causes, consequences, and implications of extinctions, preparing students for future discussions on the critical value of ecosystem services and the need for conservation efforts to mitigate further losses of biodiversity.