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From page 124... ... Using Subjective Probability and Expert Opinion In some cases, there is very little "hard" information that seems relevant to estimating the risks affecting endangered species, but some experts have accumulated experience that allows them to make informed judgments about these risks. Such expert judgment is so often available for endangered species decisions that it is of great benefit to have orclerly methods of eliciting ant! Read the entire page →
From page 125... ... Articulating an explicit framework can help link science and values and lead to better and more defensible decisions. Scientific Uncertainty in ESA Decisions For even the best-stuctied endangered species, essential pieces of information might be lacking, yet decisions must be macle. Read the entire page →
From page 126... ... The question of how many years of monitoring ciata would be required to make a decision about delisting the northern spotted owl can be answered only with reference to the level of confidence requirecl, which can be cletermined only with reference to the objectives of spotter! owl management (Taylor and Gerrodette, 19931. Read the entire page →
From page 127... ... reinforced this point in their discussion of using statistical power analyses to design and evaluate monitoring schemes for endangered species. TABLE 8-1 Consequences of Making Two Types of Statistical Errors When Evaluating Scientific Data on Endangered Species Type 1 Error Type 2 Error Reject true null hypothesis Claim an effect when none exists Protect species more than necessary Lose scientific credibility Increase socioeconomic costs more than necessary Accept false null hypothesis Claim no effect when one exists Protect species less than necessary, even lose species Lose practical, and scientific, credibility Permit activities that should not have been approved Source: Adapted from Noss (19921. Read the entire page →
From page 128... ... The alternative hypothesis is that the population size in 1990 is smaller than the population size in 1980. We test the null hypothesis that there is no difference between the population sizes in 1980 and in 1990. Read the entire page →
From page 129... ... Population estimates and other data on endangered species are often poor, which means that the failure to reject the null hypothesis (a Type 2 error) often stems from inadequate statistical power rather than any basis in fact. Read the entire page →
From page 130... ... 0) m A: m o Q , }EJECT f , - I PO~-0.67 j IggOd~8 i i 1 JJ DO NOT DIRECT ~_ \t 1980 dbtriLntion 0200 400 600 800 1000 1200 1400 1600 1800 2DOO ESTIMATED POPULATION SIZE meainm ~ (A or - 030 m IS' m o CL. Read the entire page →
From page 131... ... PHA (PROBABILillY OF TYPE 1 ERROR) Figure S-2 Tradeoffs between statistical power and probability of making Type I errors for population-size estimates of varying precision. Read the entire page →
From page 132... ... Thus, the null hypothesis of no impact on an endangered species might not be rejected when it shouicl have been (Taylor and Gerrodette 1993~. As a result, conservation measures that shouIct be undertaken will not be. Read the entire page →
From page 133... ... In other words, it is advantageous to make the assumptions and their pre~iicted consequences explicit. Listing Decisions Another area where we are concerned about asymmetric risk functions for endangered species is in decisions to list them. Read the entire page →
From page 134... ... ~2~) recognizes that designating critical habitat might have socioeconomic costs and directs those implementing the act to weigh benefits to the listed species against these costs. Read the entire page →
From page 135... ... However, as explained in the chapter on species concepts, taxonomic ranking does not necessarily reflect the same degree of phylogenetic distinctiveness among all groups of organisms. 135 Resolving Conflicts Among Interest Groups Parties with a stake in the outcome of ESA decisions include conservationists; developers; other private and public industries; private individuals; acaclemics; local, state, and fecleral agencies; tribes; and others. Read the entire page →
From page 136... ... Forest Service, Bureau of Land Management, and state wildlife agencies, all of which have ESA responsibilities, have included decision analysis and population viability analysis as tools for endangered species management. In some cases, more thorough, quantitative analyses will be needed, with consultation from a decision analyst or population biologist. Read the entire page →
From page 137... ... However, it is critical to understand that achieving the same biological risks for listed species might well entail different management policies on public and private lancIs, because public and private entitities behave differently from each other. No implementation of the Endangered Species Act can be fully successful without recognition of these differences. Read the entire page →
From page 138... ... 1991. Reconciling Conflicts Under the Endangered Species Act: The Habitat Conservation Planning Experience. Read the entire page →
From page 139... ... 1991. Application of alternative dispute resolution to Endangered Species Act 139 interagency consultations. Read the entire page →
From page 140... ... 1993. The uses of statistical power in conservation biology: the vaquita and northern spotted owl. Read the entire page →
From page 141... ... 1982. Prohibitive Policy: Implementing the Federal Endangered Species Act. Read the entire page →
From page 143... ... Nonetheless, the committee concludes that none of the scientific uncertainties discussed below is great enough to make the ESA unworkable. ECOSYSTEM-BASED PROTECTION A stated purpose of the ESA is "to provide a means whereby the ecosystems upon which endangered species and threatened species depend may be conserved ...." The means to this end is the listing of individual species. Read the entire page →
From page 144... ... Therefore, despite the need for more knowledge, experience, management tools and, in some cases, social acceptance, ecosystem management offers promise. INADEQUATE KNOWLEDGE OF SPECIES AND THEIR ROLES IN ECOSYSTEMS The Endangered Species Act has been applied almost exclusively to vertebrates, invertebrates, and vascular plants. Read the entire page →
From page 145... ... Dynamics of Natural Populations Recovery plans often set goals based on target population sizes. Equally important is the need to stabilize the mean population density. Read the entire page →
From page 146... ... Do Minimum Viable Population Sizes Exist? A popular heuristic concept in conservation biology is that of a minimum viable population size (MVP) Read the entire page →
From page 147... ... FEASIBLE MANAGEMENT STRATEGIES Perhaps the paramount challenge to future managers of endangered species concerns the degree to which management and recovery plans can be developed within a framework that incorporates a range of continuing human activities. Numerous issues remain unresolved, such as the design of reserves, reconstruction of habitat, the usefulness of captive breeding and supplementation programs, and the effects of environmental change. Read the entire page →

From page 124...

... Using Subjective Probability and Expert Opinion In some cases, there is very little "hard" information that seems relevant to estimating the risks affecting endangered species, but some experts have accumulated experience that allows them to make informed judgments about these risks. Such expert judgment is so often available for endangered species decisions that it is of great benefit to have orclerly methods of eliciting ant!