1) Population reduction rate A critically endangered species’ population has declined between 80 and 90 percent. This decline is measured over 10 years or three generations of the species, whichever is longer.
A species is classified as critically endangered when its population has declined at least 90 percent and the cause of the decline is known. A species is also classified as endangered when its population has declined at least 80 percent and the cause of the decline is not known.
2) Geographic range A critically endangered species’ extent of occurrence is less than 100 square kilometers (39 square miles). A critically endangered species’ area of occupancy is estimated to be less than 10 square kilometers (4 square miles).
3) Population size A species is classified as critically endangered when there are fewer than 250 mature individuals. A species is also classified as critically endangered when the number of mature individuals declines by at least 25 percent within three years or one generation, whichever is longer.
4) Population restrictions A species is classified as critically endangered when its population is restricted to less than 50 mature individuals. When a species’ population is this low, its area of occupancy is not considered.
5) Probability of extinction in the wild is at least 50 percent within 10 years or three generations, whichever is longer.
Critically Endangered Species: Bolivian Chinchilla Rat The Bolivian chinchilla rat (Abrocoma boliviensis) is a rodent found in a small section of the Santa Cruz region of Bolivia. It is critically endangered because its extent of occurrence is less than 100 square kilometers (39 square miles).
The major threat to this species is loss of its cloud forest habitat. People are clearing forests to create cattle pastures.
Critically Endangered Species: Transcaucasian Racerunner The Transcaucasian racerunner (Eremias pleskei) is a lizard found on the Armenian Plateau, located in Armenia, Azerbaijan, Iran, and Turkey. The Transcaucasian racerunner is a critically endangered species because of a huge population decline, estimated at more than 80 percent during the past 10 years.
Threats to this species include the salination, or increased saltiness, of soil. Fertilizers used for agricultural development seep into the soil, increasing its saltiness. Racerunners live in and among the rocks and soil, and cannot adapt to the increased salt in their food and shelter. The racerunner is also losing habitat as people create trash dumps on their area of occupancy.
Critically Endangered Species: White Ferula Mushroom The white ferula mushroom (Pleurotus nebrodensis) is a critically endangered species of fungus. The mushroom is critically endangered because its extent of occurrence is less than 100 square kilometers (39 square miles). It is only found in the northern part of the Italian island of Sicily, in the Mediterranean Sea.
The leading threats to white ferula mushrooms are loss of habitat and overharvesting. White ferula mushrooms are a gourmet food item. Farmers and amateur mushroom hunters harvest the fungus for food and profit. The mushrooms can be sold for up to $100 per kilogram (2.2 pounds).
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