Methods of Measuring Absolute Density

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# Methods of Measuring Absolute Density - PowerPoint PPT Presentation

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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Presentation Transcript
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