N e is always some fraction of the total population

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FIELD STUDY: ANALYSIS OF GRIZZYKY BEAR POPULATIONS:1stpopulation viability analyses was conducted in 1978 by Mark Shaffer (DUKE UNIVERSITY)long-termstudy of grizzly bears in Yellowstone National Parksurrounding areasYellowstone grizzly population declined dramatically after park garbage dumps were closed in 1971population was listed as threatenedthe decline had stoppedpopulation was smaller than it hadbeenShaffer tried to determine viable sizes for the bear populationgiven a suitable habitat, apopulation of 70-90 grizzly bears would have about a 95% chance of surviving for the next 100 yearsalarger population would have twice as long a survivalIn 2013the grizzly population increased They also have less genetic variabilityoDecline and isolation in genetic variability were not as severe as fearedthey were even low inthe 1900sHow might the increase Neand genetic variation?oMigration between isolated population of grizzlies increases both effective and total populationsizesIntroducing 2 unrelated bears each decade into a population of 100 individuals wouldreduce the loss of genetic variation by halfDECLINING- POPULATION APPROACH:Focuses in threatened and endangered populations that show a downward trendeven if population isfar above its minimum viable populationDistinction between a declining population (which is not always small)small population (not alwaysdeclining) is less important than the different priorities of the two approachessmall population
approach emphasizes smallness itself as an ultimate cause of a population’s extinctionloss of geneticdiversity or via chance events such as winter storms or hurricanesIn contrastdeclining population approach emphasizes the environmental factors that caused apopulation decline in the first placeoi.e.) an area is deforestedspecies that depend on trees will decline in abundance and becomeslocally extinct Steps for Analysis and Intervention:

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