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Lab 4: Estimating population size
Introduction
: Knowing the size of a population can be very valuable when trying to answer ecological
questions. Among other things, we can use such information to understand where organisms actually
live, what habitats they prefer, and whether or not the population is changing over time.
Counting each member of a population can be practically impossible; imagine trying to count each ant
invading the trashcans around RCC. Therefore, ecologists must rely on sampling techniques for estimates
of population size. One common technique is a
Mark/Release/Recapture
method first attributed to
C.G.J. Peterson (1896) who estimated fish populations in the North Sea. The method involves capturing
and marking a sample of organisms, releasing them, and then resampling the same population at a later
time. We want to know the total number of individuals in the population (N) at the time of sampling. If
the number of individuals marked in the first sample = n
1
, then the proportion of individuals marked in
the population = n
1
/N. At resampling, if we capture a number of marked individuals (x) and a number of
unmarked individuals (u) for a total of x+u=n
2
, then the proportion of marked individuals in the second
sample = x/n
2
. We can expect that the proportion of marked individuals in the second sample equals the
proportion in the initial sample (n
1
/N = x/n
2
) and do a little algebra to estimate N.
N = n
1
×
n
2
/x
This method makes the following ASSUMPTIONS:
1)
marked and unmarked individuals do not change marking status.
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- Fall '11
- PrestonGalusky
- Pillbugs, unmarked pillbugs, extra pillbugs, pillbugs molt
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