70 • Technologies To Maintain Biological Diversity 



Box 3-C. — Definitions of Threatened Status 



Two sets of definitions are used to classify the status of threatened species. Definitions based 

 on the Endangered Species Act of 1973 are used in the United States. All other countries' lists of 

 endangered species follow the definitions promulgated by the International Union for Conservation 

 of Nature and Natural Resources (lUCN). The two sets of definitions are technically not compatible 

 mainly because of differences in the concept of extinction and the lUCN inclusion of taxa rather 

 than species. 



Three technical definitions are used for classification of status in the United States: 



1. An endangered species is in danger of extinction throughout all or a significant portion of its 

 range. 



2. A threatened species is likely to become an endangered species within the foreseeable future 

 throughout all or a significant portion of its range. 



3. Critical habitats are areas essential for the conservation of endangered or threatened species. 

 The term may be used to designate portions of habitat areas, entire areas, or even areas outside 

 the current range of the species. 



The lUCN categories include five definitions: 



1. Extinct taxa are species, or other taxa such as distinct subspecies, that are no longer known 

 to exist in the wild after repeated search of their type localities and other locations where they 

 were known or were likely to have occurred. 



2. Endangered taxa are in danger of extinction and their survival is unlikely if the factors caus- 

 ing their vulnerability or decline continue operating. 



3. Vulnerable taxa are declining and will become endangered if no action is taken to intervene. 



4. Rare taxa are so rare that they could be eliminated easily but are under no immediate threat 

 at present and have populations that are more or less stable. 



5. Intermediate taxa belong in one of the above categories, but information is not sufficient to 

 determine exactly which one (47). 



SOURCES: M.J. Bean, The Evolution of National Wildlife Law {New York: Praeger Publishers, 1983); H. Synge, "Status and Trends of Wild 

 Plant Species," OTA commissioned paper, 1985. 



however, the numbers of threatened species do 

 give some indication of the scope of the 

 problem. 



Nearly all industrial countries now have lists 

 of threatened plant species. In Europe, all but 

 five countries have such lists, and four of those 

 five will have them soon (47). In the United 

 States, many lists and reports cover both the 

 Nation and individual States. Table 3-2 sum- 

 marizes some information from the endangered 

 plant species lists. 



In North America, about 10 percent of the 

 plant species are listed as rare or threatened. 

 Many are plants endemic to small areas in Cali- 

 fornia. A higher proportion of species are listed 

 in Europe because of extensive threats to vege- 

 tation in the northern countries and the nar- 



row endemism of many species in the Medi- 

 terranean countries. Data from the Soviet 

 Union emphasize horticultural plants and are 

 less complete than for Europe. For temperate- 

 zone Southern Hemisphere countries, the lists 

 are also dominated by narrow endemic plants 

 from the Mediterranean climate regions (47). 



Oceanic islands, because of geographic iso- 

 lation during the millennia of evolution, typi- 

 cally have a very high proportion of endemic 

 species. These areas are particularly vulnerable, 

 because they are not adapted to animals and 

 aggressive weeds that may be introduced by 

 humans. Lists of threatened plants have been 

 prepared for many such islands. Table 3-3 in- 

 dicates how severe the threats are for islands 

 with 50 to 1,000 endemic species. 



