Background Information: The Lincoln Index

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Background Information: The Lincoln Index

The Lincoln Index is a method which is used to estimate and sample the size of closed populations. This method was discovered in by the American ornithologist Frederick C. Lincoln in 1930. The Lincoln Index provides a way to measure, sample and estimate population sizes of individual animal species. It is based on the capture, mark, release and recapture technique. The mark and recapture method involve random sampling of a population of animals and then mark all of the individuals that is captured in a recognizable way but is non-harmful and does not expose them to higher predation levels than non-marked individuals. The marked animals are then released back into the original population and left to mingle with the general population for a suitable period of time to allow complete remixing of the marked individuals with the population. Once they have become thoroughly mixed into the population again, the population is then resampled. There must be enough time allowed to elapse for complete mixing of the population to have happened.

This process can be simplified in equation, easy steps and symbols as follows:

n1 = number of animals first marked and released.

n2 = number of animals captured in the second sample

m2 = number of marked animals in the second sample

N = Total Population

m2/n2 = n1/N

N = n1 x n2 / m2

-If the number of animals recaptured in the second sample (n2) is less than 8, the estimation of the population is likely to be biased.

-If there are losses from the population during the remixing period, then the estimation would be for the size of the population at the time of the first sampling session.

-If there are gains in the p...

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...in size as a replacement for straw bits. As the data shows, some the proportion of marked straw bits in the first capture to the total population (n1/N) is not equal to the proportion of marked straw bits in the second capture to the total straw bits in the second capture (m2/n2). For example, 20(n1)/100(N)≠3 (m2 in the 4th trial)/10(n2). Since this is a random sampling, it is impossible to control the results especially the number of marked straw bits in the second capture. The container for straw bits is shaken for the mixing between marked straw bits and unmarked straw bits. However, it is not sure that whether the population is mixed thoroughly or not. Some marked straw bits may stuck in some corners with other straw bits even after the mix. Again this is a process of random sampling and it is unpreventable for the marked straw bits’ inability to mix thoroughly.

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