Methods of Measuring Absolute Density

1. Methods of Measuring Absolute Density • Total counts - count all the organisms present in a population • Transect or quadrat sampling - counts along a known distance or in a known unit area (small). Represents a subsample of the population. • Mark-recapture methods - capture individuals, mark them in some way, resample and examine the proportion of marked to unmarked individuals.

2. Methods of Sampling Relative Density • Trap - any device that captures an organism • Fecal pellets - counts of pellets in an area (must be able to recognize species) • Vocalization frequencies - birds or frogs. DNR uses this to estimate ruffed grouse densities • Pelt records - recorded at trading stations and DNR offices for mammals of commercial value • Catch per unit effort - commonly applied in fisheries. How many fish are caught for some sample time.

3. Methods of Sampling Relative Density • Percentage ground cover - for plants or sessile animals. • Feeding capacity/damage - amount of bait taken or vegetation destroyed based back on known feeding rates • Roadside counts - number of organisms (typically birds) observed while driving some standard distance. Used for estimating pheasant and birds of prey (red-tailed hawks).

4. Calculations for a Life Table x = age interval (days, months, years) nx = the number of survivors at age interval x dx = number of organisms dying from the beginning of x to the beginning of age x + 1 lx = proportion of organisms surviving to beginning of age interval x qx = rate of mortality between the beginning of age interval x and the beginning of age x + 1

5. Calculations for a Life Table Lx = average number alive from age interval x to x + 1 Tx = “units of individuals times time units” ex = mean life expectancy at the start of age x