POPULATION ESTIMATION
LAB
How do you estimate the size of a population?
Introduction
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Measure of population density is essential to many
ecological investigations
Counting of every individual may not be possible,
let alone practical
How would you go about estimating
the size of a forest community?
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Transect Line Study
- Locate and run transects
- Collect data at each sample point
- Interpret data
How would you go about estimating
the size and of a forest community?
http://www1.esc.edu/personalstaff/kwatson/fieldwork_site/tree_transects.htm
How would you go about estimating
the size of an understory community?
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Quadrants
- Lay down a 1 meter squared quad or a hula
hoop
- Identify and count everything in the quad
How would you go about estimating
the size of an understory community?
http://www.science.oregonstate.edu/bpp/faculty/wilson/Work
ersQuad_PR%20(2).jpg
How would you go about estimating
the size of an animal population?

Live Trapping
- Lay out transects
- Place traps about 10 meters apart using several
transect lines typically at dusk
- Check traps at dawn
- Mark captured animals
- Reset the traps and repeat for several days
How would you go about estimating
the size of an animal population?
http://www.stolaf.edu/depts/environmental-studies/courses/es399%20home/es-39905/Projects/Jared's%20Senior%20Seminar%20Research%20Page/htt.htm
What do you do with the data?
Lincoln-Peterson Index
 Sample of population (size N) is taken
 Animals are marked (m) and released back into the
population
 Proportion of population is now marked (m/N)
What do you do with the data?


Second sample is (size n) is taken later presumably
some of the them are already marked (r)
Proportion of trapped individuals that are marked
(recaptured) in second sample (r/n) is crucial to
estimating population size
What do you do with the data?
Lincoln-Peterson Index
Let
N= number of animals in the population
m= number of animals marked in the first sample and
released
m/N= proportion of marked animals in the population
r= number of recaptured animals in the second
sample
n= total number of individuals in the second
sample
Then
r/n= proportion of the marked animals in the second
sample
What do you do with the data?
If the sampling is unbiased, then r/n=m/N.
To estimate N, rearrange the above equation to yield
N=m*n/r
What assumptions are made with this
method?
1.
2.
3.
Sampling is random. Every individual must have an
equal probability of capture.
The marked animals must be mixed thoroughly
and randomly into the population so that the
second sample will accurately reflect the
population.
The population size must not change between the
two samples.
Mark-Recapture Lab
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Estimate the size of a bean population through the
mark-recapture method and Lincoln-Peterson Index
Mark the beans by replacing the captured whitecolored beans with dark-colored beans
Repeat the lab using a larger sampler (beaker)
Remember to resort your beans at the end!