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How many individuals did you count?
The individuals caught in camera traps represent part of the population,
but not necessarily all of it. There may be individuals living in
this area that did not walk in front of a camera trap during the survey
period. So how do we estimate the real size of the population, if
it's not just the number you counted above?
Scientists do this through a method called mark-recapture. The premise
of the method is that you can estimate population size by looking
at the number of animals that are "recaptured" during a
second survey period.
A basic mark -recapture formula that
can be applied in order to estimate the population size is the following:
N= Estimated Population Size
M= # of individuals Marked in first survey
C= # of individuals Captured in second survey
R= # of individuals
Recaptured in second survey |
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1. A second survey was conducted
3 months after the one above and 15 jaguars were recorded. Of
those 15 jaguars (C), 13 were jaguars seen during the first
survey (R). If you apply the formula using the number of individuals
you counted above (M), what is the estimated population size?
2. Your study area was 140 square kilometers. Using the estimated
population size you just calculated, find the jaguar population
density. Remember, density is calculated by dividing the size
of the area by the estimated population size.
3. In some camera traps you found multiple individuals, do you
think these jaguars are seeing each other? Why would jaguars,
solitary animals, have territories that overlap?
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 ©
2006 Wildlife Conservation Society.
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