Species populations are loosely grouped into six major categories. The four categories of endangered species are vulnerable, endangered, critically endangered, and extinct in the wild.

Illustration by Mary Crooks

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  • What makes a creature a vulnerable species? What makes it endangered? Scientists at the International Union for the Conservation of Nature (IUCN) use these criteria to group animal populations worldwide.

  • Term Part of Speech Definition Encyclopedic Entry
    criteria Plural Noun

    set of standards or rules.

    endanger Verb

    to put at risk.

    endangered species Noun

    organism threatened with extinction.

    Encyclopedic Entry: endangered species
    International Union for the Conservation of Nature (IUCN) Noun

    environmental organization concerned with preserving natural ecosystems and habitats.

    population Noun

    total number of people or organisms in a particular area.

    scientist Noun

    person who studies a specific type of knowledge using the scientific method.

    vulnerable species Noun

    level of conservation between "near threatened" and "endangered." Vulnerable is the lowest of the "threatened" categories.