SELKIRK GRIZZLY BEAR DNA MARK/RECAPTURE ANALYSIS - PowerPoint PPT Presentation

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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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Selkirk grizzly bear dna mark recapture analysis l.jpg

SELKIRK GRIZZLY BEARDNA MARK/RECAPTURE ANALYSIS


Mark recapture explained l.jpg

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


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MARK/RECAPTURE

N = Popn size

M = # initially marked

n = # caught in 2nd effort

m = # recaptured


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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


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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


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What does this have to do with grizzly bears?


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USE DNA as a MARK


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  • 50 barbed-wire enclosures

  • 470 sq miles

  • Visited each site 4 times

  • Collected over 1,200 hair samples


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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


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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


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COMPARISON: PROCTOR 2005


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CAUTIONS about mark/recap

  • Point Estimate – says nothing about trend

  • Density cannot be extrapolated to the entire ecosystem

  • No info on reproduction


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THE END


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