Question

Field biologists are faced with a number of generally impossible tasks, and one of the most significant is the task of determining how many individuals are contained in a wild population. It is often simply impossible to literally count them all. This lab exercise simulates one of the important techniques used to estimate what can't be directly measured. This tool is based upon statistical assumptions. The scientist is assuming that if he or she captures a random sample of the wild population, that sample will tend to be representative of the whole population. The investigator first sets traps which will capture a number of the animals of the population without hurting them. Every attempt is made to insure a random capture. The captured animals are then marked in some way — tagged or tattooed, for instance — and released back into their environment. A second random capture is then made. The animals are inspected for the presence of the marks applied to the originally captured animals. The assumption is then made that the percentage of the second group of captured animals who bear the marks is the same as the percentage of marked animals in the whole population. In other words, if 20% of the second capture are marked, the scientist assumes that the first, marked group of animals represent 20% of the entire population. Based upon this assumption it is then possible to calculate a population estimate. So why would an ecologist need to calculate the size of a wild population? Of course, it may simply be part of the data being collected in a study of the population and ecosystem. But wildlife managers also use information like this to make decisions about animal control efforts. For instance, if a population has seriously exceeded its carrying capacity, the wildlife manager might authorize the issuance of an appropriate number of hunting permits to attempt to bring the population size back down to a healthy level. If the estimate of population size is below carrying capacity, of course, no hunting permits would be issued. This lab exercise is a simulation of this technique.

          Field biologists are faced with a number of generally impossible
tasks, and one of the most significant is the task of determining
how many individuals are contained in a wild population. It is
often simply impossible to literally count them all. This lab
exercise simulates one of the important techniques used to estimate
what can't be directly measured.
This tool is based upon statistical assumptions. The scientist
is assuming that if he or she captures a random sample of the wild
population, that sample will tend to be representative of the whole
population. The investigator first sets traps which will capture a
number of the animals of the population without hurting them. Every
attempt is made to insure a random capture. The captured animals
are then marked in some way — tagged or tattooed, for instance —
and released back into their environment. A second random capture
is then made. The animals are inspected for the presence of the
marks applied to the originally captured animals. The assumption is
then made that the percentage of the second group of captured
animals who bear the marks is the same as the percentage of marked
animals in the whole population. In other words, if 20% of the
second capture are marked, the scientist assumes that the first,
marked group of animals represent 20% of the entire population.
Based upon this assumption it is then possible to calculate a
population estimate.
So why would an ecologist need to calculate the size of a wild
population? Of course, it may simply be part of the data being
collected in a study of the population and ecosystem. But wildlife
managers also use information like this to make decisions about
animal control efforts. For instance, if a population has seriously
exceeded its carrying capacity, the wildlife manager might
authorize the issuance of an appropriate number of hunting permits
to attempt to bring the population size back down to a healthy
level. If the estimate of population size is below carrying
capacity, of course, no hunting permits would be issued.
This lab exercise is a simulation of this technique.

Added by Sydney F.

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