5.4: The Biodiversity Crisis

BIOL 101- Environmental Science · LibreTexts

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    Biodiversity Is Unevenly Distributed 

    Biodiversity is not evenly distributed across Earth (Fig a). In general, biodiversity is highest near the equator and decreases toward the poles. Tropical regions such as rainforests contain large numbers of species and many endemic species, which are species found nowhere else on Earth. These areas often become priorities for conservation because they contain unique forms of life. 

    Biodiversity Hotspots

    Some regions contain exceptionally high biodiversity and are under significant threat from human activities. These regions are called biodiversity hotspots. To qualify as a hotspot, an area must contain at least 1,500 endemic plant species (species found nowhere else on Earth) and have 30% or less of its original natural habitat remaining.

    Biodiversity hotspots are a high priority for conservation because protecting a relatively small area can help preserve a large number of unique species. Many hotspots contain plants and animals that exist nowhere else on the planet.

    Conservation International has identified 36 biodiversity hotspots worldwide (figure \(\PageIndex{a}\)). Together, these areas cover only about 2.5% of Earth's land surface, yet they contain more than half of the world's endemic plant species and nearly 43% of endemic birds, mammals, reptiles, and amphibians.

    Despite covering a small fraction of Earth's land area, biodiversity hotspots provide an estimated 35% of the ecosystem services that support human well-being, including food production, water purification, pollination, climate regulation, and other benefits that people depend on every day.

    Biodiversity hotspots cluster along coasts and islands, where many unique species live.

    Figure \(\PageIndex{a}\) Map of the world's biodiversity hot spots, all of which are heavily threatened by habitat loss and degradation. By Conservation International - Own work, CC BY-SA 4.0. 

     

    Biodiversity Loss

    Although extinction is a natural process, human activities have greatly increased extinction rates.
    The major causes of biodiversity loss are:

    1. Habitat destruction and fragmentation
    2. Invasive species
    3. Overharvesting of natural resources
    4. Pollution
    5. Climate change

    Together, these pressures are causing species to disappear at rates far above natural background levels of extinction. 

     

    Case Study: Lake Victoria Cichlids

    Lake Victoria in East Africa once contained hundreds of species of cichlid fish, each adapted to a different habitat or food source (figure \(\PageIndex{b}\)). Many of these species declined rapidly after the introduction of the Nile perch, a large predatory fish. Habitat degradation and increased fishing pressure also contributed to biodiversity loss. Scientists estimate that many species disappeared before they were even fully studied. This example illustrates how human activities can rapidly reduce biodiversity.

    Illustration
    Figure \(\PageIndex{b}\): Cichlids of the African rift lake system. By original figureː Joana I. Meier, David A. Marques, Salome Mwaiko, Catherine E. Wagner, Laurent Excoffier & Ole SeehausenEditing by Dennis Pietras, Buffalo, NY USA - originally figure 1 of "Ancient hybridization fuels rapid cichlid fish adaptive radiations" doi:10.1038/ncomms14363 http://www.nature.com/articles/ncomms14363Minor editing and conversion to jpg by Dennis Pietras, CC BY-SA 4.0, https://commons.wikimedia.org/w/inde...curid=56290753

    Conservation of Biodiversity

    Conservation biologists work to protect biodiversity by:

    • Protecting habitats
    • Restoring ecosystems
    • Managing threatened species
    • Creating protected areas
    • Supporting sustainable resource use

    Conservation efforts help preserve biodiversity and maintain the ecosystem services that support human societies.

    Summary

    Biodiversity refers to the variety of life on Earth and includes genetic, species, and ecosystem diversity. Biodiversity provides important ecosystem services and supports human well-being. However, biodiversity is declining because of habitat destruction, invasive species, pollution, overharvesting, and climate change. Protecting biodiversity helps maintain ecosystem resilience, supports conservation goals, and preserves the ecosystem goods and services that humans need for survival. 

     

    Attribution

    This page was heavily revised and rewritten by Erin Rempala and contains adapted content from Openstax and is licensed CC BY-NC-SA 4.0.

    This page titled 5.4: The Biodiversity Crisis was last modified on Tue, 28 Jul 2026 14:07:40 GMT and is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Erin Rempala via source content that was edited to the style and standards of the LibreTexts platform.