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 Quadrat = a 4-sided area within which you do a survey/count Density = number of individuals/area

Transect Quadrat

Population counts are important to: 1.Determine threatened or endangered species 2.Set hunting seasons and bag or creel limits 3.Plan for future management or evaluate existing programs

Counting Techniques 1.Rabbits – road kill/car survey 2.Quail and pheasant – bird calls in spring 3.Ducks and geese – low flying planes Transects used 4. Squirrels – count last years crop of nuts and acorns in Aug/Sept.

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 1.Trap/capture animals and mark them = T 2.Release back into habitat 3.Released animals redistribute back in original population (assume random redistribution) 4.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

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 1.Between two samples there is birth, death, immigration (in), and emigration (out) 2.Tag should not be a factor to survival