Our IJvinn Rfs<Hin'fs — Human Influences 



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Resources available for conservation of 

 species and ecosystems invariably are in 

 short supply relative to the needs for those 

 resources. Targeting conservation and man- 

 agement actions toward those species and 

 ecosystems in greatest need, and where 

 opportunities for success are greatest, 

 requires clearly established priorities. 

 Accordingly, setting priorities is a necessary 

 prerequisite for effective biodiversity con- 

 servation and ecosystem management. 



Many systems and methods for setting 

 priorities and determining endangerment sta- 

 tus have been developed, including those 

 used by the U.S. Fish and Wildlife Service, 

 the lUCN (World Conservation Union; for- 

 merly International Union for the Conserv- 

 ation of Nature and Natural Resources), and 

 many individual states. Among the most 

 widely applied systems is the biodiversity 

 status-ranking system developed and used by 

 the Natural Heritage Network and The Nature 

 Conservancy (Master 1991; Morse 1993; 

 Stein 1993). This ranking system has been 

 designed to evaluate the biological and con- 

 servation status of plant and animal species 

 and within-species taxa as well as ecological 

 communities. For status-ranking purposes, 

 collectively these are all referred to as "ele- 

 ments" of natural diversity (Jenkins 1988). 



Status ranks are based primarily on objec- 

 tive factors relating to a species' rarity, popu- 

 lation trends, and threats. Four aspects of rar- 

 ity are considered: number of individuals, 

 number of populations or occurrences, rarity 

 of habitat, and size of geographic range. 

 Ranks are assigned according to a rigorous 

 and standardized process, with all supporting 

 information documented in Heritage Program 

 data bases. Ranking is based on an approxi- 

 mately logarithmic scale, ranging from (1) 

 critically imperiled to (5) demonstrably 

 secure (Table). Typically species with ranks 

 from one to three would be considered of 

 conservation concern and broadly overlap 

 with species that might be considered for 

 review under the Endangered Species Act or 

 similar state or international statutes. 



For conservation priorities to be set at 



Table. Definition of biodiversity status ranks. 



Rank Definition 



GX Presumed extinct; not located despite searches 

 GH Of fiislorical occurrence; possibly extinct but some 



expectation of rediscovery 

 G1 Critically impenled; typically 5 or fewer occurences or 



1.000 or fewer individuals 

 G2 Imperiled; typically 6 to 20 occurrences or 1 .000 to 



3,000 individuals 

 G3 Rare or uncommon but not imperiled: typically 21 to 



100 occurrences or 3,000 to 10,000 individuals 

 G4 Uncommon but not rare: apparently secure, but v»ith 



cause for some long-term concern; usually more than 



100 occurrences or 10,000 individuals 

 G5 Common; demonstrably widespread, abundant, and 



secure 



Status of U.S. Species: 



Setting Conservation 



Priorities 



by 



Bruce A. Stein 



Lawrence L. Master 



Larry E. Morse 



Lynn S. Kutner 



Melissa Morrison 



The Nature Conservancy 



local as well as rangewide scales, ranking is 

 carried out at three hierarchical levels: subna- 

 tional (e.g., state), national, and global. Thus, a 

 species may be relatively common and secure 

 globally (G4), but within a given state may be 

 critically imperiled (SI). The combined rank 

 within that state (G4/S1) allows local priori- 

 ties to be set within a global context. 



overall status, trends, or threats. Indeed, ranks 

 initially assigned to some poorly known 

 species may reflect the inadequate state of 

 knowledge about the organism more than its 

 actual biological status. The very process of 

 assigning these ranks and documenting the 

 gaps in our understanding, however, works as 

 a powerful tool in setting priorities for addi- 

 tional inventory and research. The increased 

 inventory attention accorded highly ranked 

 (i.e., rare) species tends to improve under- 

 standing of the species' distribution and sta- 

 tus, often showing the species to be more 

 common or secure than previously known 

 and, therefore, of lesser concern from a con- 

 servation perspective. 



The Natural Heritage Network is a dis- 

 tributed data-base network operating on the 

 principle of shared information-management 

 concepts and shared responsibilities. Each 

 state is responsible for assessing the status of 

 each species and natural community within 

 its jurisdiction and for assigning and docu- 

 menting a state rank for those elements. For 

 each species, however, one appropriate node 

 in this distributed data-base network is 



b, 

 350 

 300 

 S 250 

 i.200 

 "5 150 

 5 100 

 50 - 

 0' 



^Ih Vn ■ 



hjL 



Butterflies 



Crayfish 



Mussels 



o 2 



Angiosperms 



Pteridophyles 



Gymnosperms 



Figure. GH/GX - potentially e.xtinct; Gl to G5 rank species from rarest (01) to most common (G5). 

 a - status ranks of U.S. vertebrate species (fish include freshwater only); b - status ranks of selected 

 invertebrate groups: native U.S. species of butterflies, crayfish, and freshwater mussels; c - status 

 ranks of native U.S. flowering plant species; and d - status ranks of native U.S. fern and conifer 

 species. 



The natural world is extremely dynamic, 

 due to both intrinsic ecological factors and 

 increasing human influences. At the same 

 time, our knowledge of the distribution, abun- 

 dance, and basic biology of species and eco- 

 logical communities is imperfect, but contin- 

 ually improving. For these reasons, biodiver- 

 sity status ranks must be viewed as working 

 hypotheses based on the best available infor- 

 mation. Ranks are continually reevaluated 

 and refined as new populations are discov- 

 ered, known populations are extirpated, or 

 new or better information is available on 



responsible for maintaining the current glob- 

 al rank based on a combination of the state 

 and national-level status ranks together with 

 other available information. 



Global-level ranks have been assigned to 

 all U.S. vertebrate species, selected groups of 

 invertebrates (including all federally listed, 

 proposed, and candidate species), all vascular 

 plant species, and selected nonvascular plant 

 species (e.g., many lichens and bryophytes). 

 Preliminary global ranks also have been 

 assigned to all rare terrestrial natural commu- 

 nities for the United States. 



