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