selkirk grizzly bear dna mark recapture analysis
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SELKIRK GRIZZLY BEAR DNA MARK/RECAPTURE ANALYSIS

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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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mark recapture explained
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
mark recapture
MARK/RECAPTURE

N = Popn size

M = # initially marked

n = # caught in 2nd effort

m = # recaptured

critical assumptions
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
mark recapture example
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

slide10

50 barbed-wire enclosures

  • 470 sq miles
  • Visited each site 4 times
  • Collected over 1,200 hair samples
results
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
results13
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

cautions about mark recap
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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