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SELKIRK GRIZZLY BEAR DNA MARK/RECAPTURE ANALYSIS

SELKIRK GRIZZLY BEAR DNA MARK/RECAPTURE ANALYSIS. MARK/RECAPTURE EXPLAINED. 1 ST you catch some animals in a pop n and “mark” them Later on you catch animals in the same pop n Some of those will be new animals, some will be recaptures

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SELKIRK GRIZZLY BEAR DNA MARK/RECAPTURE ANALYSIS

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  1. SELKIRK GRIZZLY BEARDNA MARK/RECAPTURE ANALYSIS

  2. MARK/RECAPTURE EXPLAINED • 1ST you catch some animals in a popn and “mark” them • Later on you catch animals in the same popn • Some of those will be new animals, some will be recaptures • You use the ratio of “marked” to “recapture” to get a popnestimate

  3. MARK/RECAPTURE N = Popn size M = # initially marked n = # caught in 2nd effort m = # recaptured

  4. CRITICAL ASSUMPTIONS • Marks must be permanent • All animals have an equal probability of getting caught • No changes in population between initial mark and later recapture

  5. MARK/RECAPTURE example • 1st mark: Trap 20 mice, paint their toenails red • Recapture: 1 week later, trap again; catch 16 mice, 4 have red toenails So, N = (20 x 16) / 4, which equals 80

  6. What does this have to do with grizzly bears?

  7. USE DNA as a MARK

  8. 50 barbed-wire enclosures • 470 sq miles • Visited each site 4 times • Collected over 1,200 hair samples

  9. RESULTS • ID 15 different grizzly bears • 9 females, 6 males • 15 bears captured a total of 50 times • Multiple capture sessions allows for more complicated analysis • Test for diff male/female capture probability, diff capture prob among sessions, trap happy, trap shy

  10. RESULTS • Best model estimated 18 grizzly bears • 11 females, 7 males • Density 14.1 bears / 1,000 sq km (naïve estimate) 9.7 bears / 1,000 sq km (SECR estimate) 3.6 bears / 100 sq miles 2.5 bears / 100 sq miles

  11. COMPARISON: PROCTOR 2005

  12. CAUTIONS about mark/recap • Point Estimate – says nothing about trend • Density cannot be extrapolated to the entire ecosystem • No info on reproduction

  13. THE END

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