68 • Technologies To Maintain Biological Diversity 



monitoring of resource changes. At present, 

 reports are available on about 67 developing 

 countries, and nearly all describe ecosystem 

 degradation. In some places the problems are 

 the longstanding effects of unsustainable re- 

 source development; in others, the degradation 

 has increased dramatically over the last dec- 

 ade and is constraining economic development 

 (see box 3-B). 



Species Diversity 



Data to document changes in numbers and 

 distribution of species are scarce. To document 

 an extinction, the species must be named and 

 described taxonomically and accurately ob- 

 served at least once, then the loss must be 

 recorded. Most documented extinctions have 

 been of large terrestrial birds, mammals, and 

 conspicuous flow^ering plants in the temperate 

 zone and on tropical islands. 



Modern taxonomic description goes back to 

 1753, but most recognized species were de- 

 scribed much more recently, and the majority 

 of species have yet to be described and named. 

 For most of the estimated 385,000 living plant 

 species, not much more is known than can be 

 discerned from one or a few pressed, dried her- 

 barium specimens. Nevertheless, personnel and 

 financial support for the taxonomic work done 

 in museums, herbariums, universities, and 

 wildlife agencies around the world are being 

 reduced (8). 



Biologists estimate that at least two-thirds of 

 all species live in the tropics. For example, a 

 single tree in the Peruvian Amazon rain forest 

 was found to harbor 43 species of ant belong- 

 ing to 26 genera. That is a species richness about 

 equal to the ant fauna of the entire British Isles 

 (27). But two-thirds of the named species are 

 in the temperate zone. This disparity reflects 

 the historical distribution of taxonomists. In the 

 United States, for example, about 500 plant tax- 

 onomists work with 18,000 species— a ratio of 

 36 species to 1 taxonomist. Tropical vascular 

 plant species number about 190,000; about 1,500 

 taxonomists worldwide have expertise in trop- 

 ical plants, yielding a ratio of 125 to 1 (8). 



Even for conspicuous species that have been 

 named, a considerable delay is involved in 

 recording an extinction. For example, the U.S. 

 Fish and Wildlife Service conducted a status 

 review in 1985 for the ivory-billed woodpecker, 

 whose last accepted sighting had been in the 

 early 1950s. Had extinction been confirmed, 

 then the lag between extinction and confirma- 

 tion of loss could have been 30 years (16). The 

 status of this species remains in doubt, how- 

 ever, because a sighting was reported in 1986 

 (2). 



Indirect methods must be used to estimate 

 changes in species diversity, because complete 

 inventories of ecosystems would be too expen- 

 sive, and because little is known of many spe- 

 cies and the genetic attributes of populations. 

 Methods include: 



• preparing lists of species threatened with 

 extinction and monitoring those species; 



• monitoring populations of relatively well- 

 known "indicator species" where habitats 

 are being changed and inferring that other 

 species in the same ecosystem are experi- 

 encing similar changes (indicator species 

 are commonly trees, birds, large mammals, 

 butterflies, or flowering plants); and 



• using mathematical models of species-area 

 relationships to project extinction numbers 

 likely to result from various levels of habi- 

 tat reduction. 



Lists off Tiireatened Species 



Lists of threatened animal species are pre- 

 pared by the Species Conservation Monitoring 

 Unit (SCMU) of the International Union for the 

 Conservation of Nature and Natural Resources. 

 For the United States, endangered animal lists 

 are prepared by the Endangered Species Of- 

 fice of the U.S. Fish and Wildlife Service 

 (FWS/ESO). For both the SCMU and the 

 FWS/ESO, the information is better for temper- 

 ate than for tropical species; better for terres- 

 trial than for aquatic species; and better for 

 birds and mammals than for reptiles, amphib- 

 ians, fish, and invertebrates (16). Terms used 

 in describing the status of threatened species 

 are defined in box 3-C. 



