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Extinction and Endangered Species - How Many Species Are Endangered?

threatened plants listed studied

Determining how many species of plants and animals are threatened or endangered is difficult. In fact, only a small fraction of the species in existence have even been identified and named, let alone studied in detail. Estimates of the total number of species on Earth range from 5 million to 100 million, with most estimates figuring around 10 million species worldwide. Of these, only about 1.75 million species have been named and described. According to the World Resources Institute, mammals, which are probably the best-studied group—and the one that includes humans—make up only 0.3 percent of all known organisms. Insects are a particularly rich biological group—over 750,000 insect species have been identified, with countless more to be described.

Since 1960 the World Conservation Union (IUCN), based in Gland, Switzerland, has compiled the IUCN Red List of Threatened Species, which aims to examine the status of biological species across the globe. The IUCN's most recent update on the status of plants and animals was published in 2003. Worldwide, in 2003, a total of 12,259 species examined were listed by the IUCN as either critically endangered, endangered, or vulnerable. These

Endangered and threatened species and recovery plans, 2004

Endangered Threatened
Group U.S. Foreign U.S. Foreign Total species U.S. species with recovery plans2
Mammals 69 251 9 17 346 55
Birds 77 175 14 6 272 78
Reptiles 14 64 22 15 115 33
Amphibians 12 8 9 1 30 14
Fishes 71 11 43 0 125 95
Clams 62 2 8 0 72 64
Snails 21 1 11 0 33 23
Insects 35 4 9 0 48 31
Arachnids 12 0 0 0 12 5
Crustaceans 18 0 3 0 21 13
Animal subtotal 391 516 128 39 1074 411
Flowering plants 569 1 144 0 714 577
Conifers and cycads 2 0 1 2 5 2
Ferns and allies 24 0 2 0 26 26
Lichens 2 0 0 0 2 2
Plant subtotal 597 1 147 2 747 607
Grand total 988 517 275 41 18211 1018
Total U.S. endangered—988 (391 animals, 597 plants)
Total U.S. threatened—275 (128 animals, 147 plants)
Total U.S. species—1263 (519 animals,3 744 plants)
1There are 1853 total listings (1290 U.S.). A listing is an E or a T in the "status" column of the Lists of Endangered and Threatened Wildlife and Plants. The following types of listings are combined as single counts in the table above: species listed both as threatened and endangered (dual status), and subunits of a single species listed as distinct population segments. Only the endangered population is tallied for dual status populations (except for the following: olive ridley sea turtle; for which only the threatened U.S. population is tallied). The dual status U.S. species that are tallied as endangered are: chinook salmon, gray wolf, green sea turtle, piping plover, roseate tern, sockeye salmon, steelhead, Steller sea-lion. The dual status foreign species that are tallied as endangered are: argali, chimpanzee, leopard, saltwater crocodile. Distinct population segments tallied as one include: California tiger salamander, chinook salmon, chum salmon, coho salmon, gray wolf, steelhead. Entries that represent entire genera or families include: African viviparous toads, gibbons, lemurs, musk deer, Oahu tree snails, sifakas, uakari (all species).
2There are 539 distinct approved recovery plans. Some recovery plans cover more than one species, and a few species have separate plans covering different parts of their ranges. This count include only plans generated by the USFWS or jointly by the USFWS and NMFS, and includes only listed species that occur in the United States.
39 animal species have dual status in the U.S.
SOURCE: "Summary of Listed Species: Species and Recovery Plans as of 02/09/2004," in Threatened and Endangered Species System (TESS), U.S. Fish and Wildlife Service, Washington, DC 2004 [Online] [accessed February 9, 2004]

included 5,483 animals (of 20,509 examined) and 6,774 plants (of 9,706 examined). Listed animals included:

  • 1,130 of 4,789 mammals studied (24%)
  • 1,194 of 9,932 birds studied (12%)
  • 293 of 473 reptiles studied (62%)
  • 157 of 401 amphibians studied (39%)
  • 750 of 1,532 fish studied (49%)
  • 553 of 768 insects studied (72%)
  • 409 of 461 crustaceans studied (89%)
  • 875 of 1897 snails studied (46%)
  • several species in other groups

Endangered plants identified by the IUCN included:

  • 36 of 39 true mosses (92%)
  • 42 of 52 liverworts (81%)
  • 11 of 13 club mosses (85%)
  • 98 of 164 true ferns (60%)
  • 152 of 618 conifers (25%)
  • 151 of 288 cycads (52%)
  • 5,768 of 7,734 dicotyledonous flowering plants (75%)
  • 511 of 792 monocotyledon flowering plants (65%)

Among these are 58 plant and animal species which are already extinct in the wild and continue to persist only in captivity or cultivation. Furthermore, with the exception of birds and mammals, most biological groups have yet to be thoroughly assessed by the IUCN. Further study will likely result in many more species being added to the Red List.

Table 1.2 lists the number of species identified as threatened or endangered by the U.S. Fish and Wildlife Service under the Endangered Species Act as of February 1, 2004. Of the 1,853 species listed, 1,290 are found in the United States. Among these, 988 are endangered and 275 are threatened. More than half of the United States' endangered or threatened species are plant forms. Among animals, the greatest numbers of listed species occur among fish, birds, mammals, and insects. A majority of the endangered plants are flowering plants. However, the groups with the largest numbers of endangered species are simply those which are most well-studied.

Figure 1.1 shows the number of listed U.S. species per calendar year from 1980 to 2002. During the early 1980s FIGURE 1.1
Number of species listed as endangered or threatened per calendar year, 1980–2002
endangered and threatened species were listed at an average rate of 34 species per year. During the late 1980s and the first part of the 1990s the average rate exceeded 68 species per year. The plateau in listings during the late 1990s and early 2000s reflects, in part, budgetary constraints on listing activity at the U.S. Fish and Wildlife Service.

Within the United States, endangered and threatened species are not evenly distributed but clustered in specific geographical areas. Figure 1.2 shows the number of federally listed endangered and threatened species in each state on February 19, 2004. Regions where the number of threatened and endangered species is particularly high include southern Appalachia, Florida, the Southwest, California, and Hawaii. Hawaii harbors more threatened and endangered species than any other state, despite its small size. This is due largely to the fact that a significant proportion of the plant and animal life there is endemic—that is, found nowhere else on Earth.

Species Loss—Crisis or False Alarm?

Environmental issues, which have a tendency to pit conservation against business or economic development, are often hotly debated. With respect to current threats to biodiversity, some challengers argue that the scale of loss is not as great as we imagine. They point to uncertainty regarding the total number of species, as well as the geographic distributions of species. Other challengers claim that loss of habitat and disruption by human activity are not powerful enough to cause the massive extinction being documented. Still other challengers contend that extinction is inevitable, and that the Earth has experienced, and recovered from, mass extinctions before. They conclude that the current biodiversity loss, while huge, is not disastrous.

More commonly, however, opponents of conservation argue that "green" policies such as the U.S. Endangered Species Act place the needs of wildlife before those of humans. This was the central issue in one of the most bitter recent battles over an endangered species, that concerning protection of northern spotted owl habitat. (See Figure 1.3.) In 1990 declining populations resulted in the listing of the northern spotted owl as a threatened species. In 1992 the Fish and Wildlife Service set aside 7 million acres of forestland in the Pacific Northwest—both private and public—as critical habitat for the species. Logging was banned on federal lands within these areas. Loggers protested this ban, arguing that jobs would be lost. Supporters of the ban, on the other hand, claimed that most logging jobs had already been lost and that continued logging would preserve existing jobs only for a short time. Eventually, a compromise was reached in which logging was limited to trees under a certain size, leaving the mature growth for owl habitat. By early 1993 almost all old-growth logging on federal lands had been stopped by court action.

Why Save Endangered Species?

The conservation of species is important for many reasons. Species have both aesthetic and recreational value, as the tremendous popularity of zoos, wildlife safaris, recreational hiking, and wildlife watching (bird watching, whale watching, etc.) indicate. Wildlife also has educational and scientific value. In addition, because all species depend on other species for resources, the impact of a single lost species on an entire ecosystem may be immense—in addition to being difficult to predict. Scientists have shown that habitats with greater biodiversity are FIGURE 1.2
Number of endangered or threatened species, by state or territory, 2004
more stable—that is, they are better able to adjust to and recover from disturbances. This is because different species may perform overlapping functions in a biologically diverse ecosystem. Habitats with less diversity are more vulnerable, because a disturbance affecting one species may cause the entire network of interactions to collapse. Furthermore, many species have great economic value to human beings. Plants provide the genetic diversity used to breed new strains of agricultural crops, and many have been used to develop pharmaceutical products. Aside from the economic or utilitarian reasons for preserving species, however, many people think that humankind has a moral responsibility to maintain the Earth's biodiversity. When species are lost, the quality of all life is diminished.


Some species are particularly valued by scientists because they are the last remnants of once flourishing biological groups. Examples of these include the coelacanth, one of the few species (along with lungfish) that help to document the transition from aquatic to terrestrial life in vertebrates, and the tuatara, a highly endangered reptile found only on New Zealand. The extinction of species that have no closely related species left on Earth represent particularly significant losses to the genetic diversity of the planet.


The rapid rate of species loss should also concern human beings because many are dying out due to pollution and environmental degradation, problems that affect human health and well-being as well. Species that are particularly useful in reporting on the health of ecosystems are called biological indicator species. Environmental scientists rely on sensitive indicator species just as coal miners once relied on canaries to check air safety in underground tunnels, where dangerous gases frequently became concentrated enough to be poisonous. Miners carried a canary into the mineshaft, knowing that the air was safe to breathe as long as the canary lived. If the bird started to sicken, however, miners evacuated the tunnel. In the same way, the sudden FIGURE 1.3
The northern spotted owl, which inhabits old-growth forests in the Pacific Northwest, was the subject of a lengthy battle pitting environmentalists against logging interests. (U.S. Fish and Wildlife Service)
deaths of large numbers of bald eagles and peregrine falcons warned people about the dangers of DDT, a powerful pesticide in wide use at the time. The disappearance of fish from various rivers, lakes, and seas also alerted people to the presence of dangerous chemicals in waters. During the final decades of the twentieth century, many scientists became concerned about the sudden disappearance of many amphibians, particularly frogs, all over the world. Most troubling was the fact that many species disappeared from protected parks and wildlife refuges, areas that appeared relatively pristine and undisturbed. Amphibians are believed to be particularly sensitive to environmental disturbances such as pollution because their skins are formed of living cells and readily absorb substances from the environment. Their decline is a suggestion that all may not be well.

Extinction and Endangered Species - Factors That Contribute To Species Endangerment [next] [back] Extinction and Endangered Species - Mass Extinction

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over 7 years ago

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