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Counting Populations

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Counting Populations

- 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

Transect

Quadrat

Determine threatened or endangered species

Set hunting seasons and bag or creel limits

Plan for future management or evaluate existing programs

- 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.

5. Furbearers – car/spotlights surveying at night

6. Fish – electroshocking

7. Whales – boat transect – spotters with binoculars

8. Turtles/Birds – Capture, tag, and release

- 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

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

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.

Between two samples there is birth, death, immigration (in), and emigration (out)

Tag should not be a factor to

survival