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Counting Populations

Counting Populations. Terminology. Census = to count a group of organisms Real census = actually count all individuals Sample census = count a portion/sample (multiply by area) Transect = a real or imaginary line off of which you do a survey/count

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Counting Populations

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  1. Counting Populations

  2. Terminology • Census = to count a group of organisms • Real census = actually count all individuals • Sample census = count a portion/sample (multiply by area) • Transect = a real or imaginary line off of which you do a survey/count • Quadrat = a 4-sided area within which you do a survey/count • Density = number of individuals/area

  3. Transect Quadrat

  4. Population counts are important to: Determine threatened or endangered species Set hunting seasons and bag or creel limits Plan for future management or evaluate existing programs

  5. Counting Techniques • Rabbits – road kill/car survey • Quail and pheasant – bird calls in spring • Ducks and geese – low flying planes • Transects used • 4. Squirrels – count last years crop of nuts and acorns in Aug/Sept.

  6. Counting Techniques 5. Furbearers – car/spotlights surveying at night 6. Fish – electroshocking 7. Whales – boat transect – spotters with binoculars 8. Turtles/Birds – Capture, tag, and release

  7. Capture/Recapture Method • Trap/capture animals and mark them = T • Release back into habitat • Released animals redistribute back in original population (assume random redistribution) • After a time interval, sample is taken again • Count all in second sample = n • Number of animals marked in second sample = t

  8. N = T x n/t N = number of estimated animals in population T = total captured and tagged in first trial n = number captured in second sample t = number of marked animals in second sample

  9. An Example Twenty Snapping Turtles were captured at the beginning, tagged, and released. One year later, 10 Snapping turtles were captured, 4 of which were tagged from before. Using the previous equation we can estimate the population size of the Snapping Turtles in the area. N = T x n/t N = 20 x 10/4 N = 200/4 N = 50 Snapping Turtles If the population count was done in an area of 5 square miles then the density of the turtles would be 10/square mile.

  10. Problems with this technique Between two samples there is birth, death, immigration (in), and emigration (out) Tag should not be a factor to survival

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