Counting populations
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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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Counting populations

Counting Populations


Terminology

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


Counting populations

Transect

Quadrat


Population counts are important to

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


Counting techniques

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.


Counting techniques1

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


Capture recapture method

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


Counting populations

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


An example

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.


Problems with this technique

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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