Rare and Endangered Species

By Bruce A. Stein

The Endangered Species Act of 1973 is one of the nation’s strongest pieces of environmental legislation, and embodies a societal commitment to protect the nation’s living resources and guard against the loss of our species to extinction. In the words of the Act, “the United States has pledged itself as a sovereign state …to conserve to the extent practicable the various species of fish or wildlife and plants facing extinction.” Plants and animals listed as threatened or endangered under the federal Endangered Species Act have strong legal protections in place designed to protect them from harm or harassment. This far-sighted piece of legislation recognizes the critical role of habitat conservation to the survival of these species, and focuses not just on preventing extinction, but rather on their recovery. The Act is administered (depending on the type of species) by the U.S. Fish and Wildlife Service and the National Marine Fisheries Service.

In addition to the federal Act, many states have enacted endangered species acts of their own, or have other laws protecting sensitive species. These state acts are quite variable in the protections they afford, and the types of plants and animals that are targeted for protection. Michigan State University offers a useful summary of state endangered species protection laws.

How Many Endangered Species?

Under the federal Endangered Species Act, endangered species are defined as “any species which is in danger of extinction throughout all or a significant portion of its range”, while threatened species are defined as “any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range.” As of December 2008, there were 1,358 U.S. species listed under the Act, of which 309 are regarded as threatened and another 1,049 as endangered. The U.S. Fish and Wildlife Service provides a daily updated summary of the number of listed species, known as the “boxscore.” As the chart below illustrates, however, the number of species listed can vary dramatically over time, influenced not only by biological needs, but also policy and funding availability.

This chart also highlights the importance in answering the question, “how many endangered species are there?”, of distinguishing between the number of species legally protected under the Act, and the number of species that biologically are threatened, endangered, or otherwise at increased risk of extinction. Being formally added to the federal endangered species list is an arduous regulatory process, and many other species are known to be rare or declining. NatureServe and its network of state natural heritage programs has developed a widely used system for evaluating the condition of plant and animal species and identifying those that are at increased risk of extinction, and therefore of conservation concern. Such assessments include but go well beyond those relatively few species that have been formally included on the federal endangered species list. These assessments are routinely used by government agencies, conservation organizations, and industry to identify which species are of conservation concern and may warrant special attention.

NatureServe status assessments consider about a dozen factors related to extinction risk, including the number of distinct populations, the number of individuals, the extent of a species’ range, and the trends in these populations. Based on best available information, each species is assessed for its conservation status and assigned status rank based on a one through five scale, where one is regarded as critically imperiled and five is considered abundant and secure. Assessment are carried out at both a rangewide, or “global” scale (e.g., G1 signifies a species that is critically imperiled throughout its range) as well as state level (e.g., G5S1 indicates a species that is abundant globally, but critically imperiled within a given state). Extinct (GX) and possibly extinct (GH) species are tracked separately.

Roughly 35,000 U.S. species have been assessed using the NatureServe status assessment ranks. An analysis of just those plant and animal groups that have been assessed comprehensively (totaling about 24,500 species), reveals that about 4,500 U.S. species (18% of the total) are imperiled (G1 or G2), the categories most closely reflecting listings under the Endangered Species Act. Another 3,700 species (15%) are considered vulnerable (G3). In addition, nearly 100 U.S. species already are presumed to be extinct, and another 400 are regarded as possibly extinct. Status ranks for any particular species can easily be found using the NatureServe Explorer web site.

Apart from the total number of imperiled or endangered species, it is interesting to look at the patterns of endangerment among the different groups of plants and animals (at right). While overall about one-third of species are at increased risk of extinction and of conservation concern, for certain groups the proportion is far higher. Nearly 70% of freshwater mussels, for instance, are at risk, with nearly one in ten either extinct or possibly so. Indeed, one clear pattern that emerges from these analyses is that species depending on freshwater habitats—such as mussels, crayfishes, fishes, and amphibians—are at increased peril than their upland counterparts.

Learn More

US Fish and Wildlife Service Endangered Species Program

IUCN Red List

NatureServe Explorer

NatureServe: How many endangered species are there in the United States?

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