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Mark-Recapture

Mark-Recapture. Goal is to get an estimate of total population. Trap animals, mark and release. Repeat trapping and count captures of marked individuals. Important to know if closed or open population. Closed populations. No individuals enter or leave the population between surveys.

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Mark-Recapture

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  1. Mark-Recapture • Goal is to get an estimate of total population. • Trap animals, mark and release. • Repeat trapping and count captures of marked individuals. • Important to know if closed or open population.

  2. Closed populations • No individuals enter or leave the population between surveys Survey 2 Survey 1

  3. Open populations • Individuals enter or leave the population between surveys Survey 2 Survey 1

  4. What makes a population closed? • Dispersal barriers • Large surveyed area • Slow reproduction/death rates • Short time between surveys

  5. Lincoln-Petersen method: Closed population Survey 1: Survey 2: Catch several animals Catch C animals Count recaptures (R) Mark all M animals Return animals to population Return animals to population

  6. Survey 2: Survey 1: M = 12 C = 15 R = 4

  7. Math Problem C = 15 R = 4 N = ??? M = 12 • Use the survey data to estimate the total population.

  8. To the game! • Remember rules • Play nicely with others • Don’t spill the beans!

  9. Mark-Recapture Game 1. Guess how many total beans you have. 2. Take one sample (one handful) of your population. 3. Count beans in your sample. 4. “Mark” by replacing sampled beans with the other kind. 5. Mix thoroughly!!! 6. Take another sample (one handful) of your population. 7. Count total number and number of “marked” beans in new sample. 8. Resample at least 5 times (do NOT mark, just resample).

  10. Lincoln-Peterson Method • Note that the proportion marked in the population equals the proportion marked in the 2nd sample.

  11. When would Lincoln-Petersen give you a bad estimate? • Population not closed • Marked animals more likely to be re-trapped • Marked animals likely to die • Marks fall off • Doesn’t work if no marked animals recaptured!

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