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.

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.

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).

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

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