Methods of measuring absolute density
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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.

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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.


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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.


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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 l.jpg
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


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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


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