Early zoos like the Menagerie du Jardin des Plantes were more like museums of living animals than natural habitats. Animals were kept in small display areas, with as many species as space would allow. However, the snaggletooth shark is a vulnerable species because of a severe population reduction rate. Its population has fallen more than 10 percent over 10 years. The number of sharks is declining due to fisheries, especially in the Java Sea and Gulf of Thailand. The snaggletooth shark’s flesh, fins, and liver are considered high-quality foods. They are sold in commercial fish markets, as well as restaurants. 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.

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Ebony ( Diospyros crassiflora) is a tree native to the rain forests of central Africa, including Congo, Cameroon, and Gabon. Ebony is an endangered species because many biologists calculate its probability of extinction in the wild is at least 20 percent within five generations.Many species of violets, native to tropical jungles in South America and Africa, are near threatened, for instance. They have healthy populations, but their rain forest habitat is disappearing at a fast pace. People are cutting down huge areas of rain forest for development and timber. Many violet species are likely to become threatened. Human activity can also contribute to a loss of habitat. Development for housing, industry, and agriculture reduces the habitat of native organisms. This can happen in a number of different ways. 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. Deforestation has greatly altered landscapes around the world. About 2,000 years ago, 80 percent of Western Europe was forested; today the figure is 34 percent. In North America, about half of the forests in the eastern part of the continent were cut down from the 1600s to the 1870s for timber and agriculture. China has lost great expanses of its forests over the past 4,000 years and now just over 20 percent of it is forested. Much of Earth’s farmland was once forests.

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Over generations, all of the species that are currently alive today have evolved unique traits that make them distinct from other species. These differences are what scientists use to tell one species from another. Organisms that have evolved to be so different from one another that they can no longer reproduce with each other are considered different species. All organisms that can reproduce with each other fall into one species. The Sri Lankan legume tree ( Crudia zeylanica), native only to the island of Sri Lanka in the Indian Ocean, was a giant species of legume. Peas and peanuts are smaller types of legumes. A species is classified as endangered when its population is restricted to less than 250 mature individuals. When a species’ population is this low, its area of occupancy is not considered. Population restriction is a combination of population and area of occupancy. A species is vulnerable if it is restricted to less than 1,000 mature individuals or an area of occupancy of less than 20 square kilometers (8 square miles).

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. The Siberian sturgeon is an endangered species because its total population has declined between 50 and 80 percent during the past 60 years (three generations of sturgeon). Overfishing, poaching, and dam construction have caused this decline. Pollution from mining activities has also contributed to abnormalities in the sturgeon’s reproductive system. 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. An endangered species is a type of organism that is threatened by extinction. Species become endangered for two main reasons: loss of habitat and loss of genetic variation. The World Association of Zoos and Aquariums, the international organization for zoos, is concerned with the health of animals in zoos. The focus of environmental efforts takes the form of research, captive breeding of rare animals, and conservation.

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Deforestation also threatens the world’s biodiversity. Tropical forests are home to great numbers of animal and plant species. When forests are logged or burned, it can drive many of those species into extinction. Some scientists say we are already in the midst of a mass-extinction episode. Today, zoos are meant to entertain and educate the public but have a strong emphasis on scientific research and species conservation. There is a trend toward giving animals more space and recreating natural habitats. Zoos are usually regulated and inspected by the government. Species that are not threatened by extinction are placed within the first two categories—least concern and near-threatened. Those that are most threatened are placed within the next three categories, known as the threatened categories—vulnerable, endangered, and critically endangered. Those species that are extinct in some form are placed within the last two categories—extinct in the wild and extinct.

The Cuban macaw ( Ara tricolor) was a tropical parrot native to Cuba and a small Cuban island, Isla de la Juventud. Hunting and collecting the birds for pets led to the bird’s extinction. The last specimen of the Cuban macaw was collected in 1864.