3bEstimatingPopulationSize

The lincoln peterson calculation tends to

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Unformatted text preview: -Peterson calculation tends to overestimate the population size, especially if the number of recaptures is small. Assumption 7 is often violated, because it is difficult to generate sufficient recaptures in large populations. To provide a better estimate, ecologists sometimes use multiple marks and recaptures and the Schnabel index to estimate population size: m ÂM C i N= i i =1 m ÂR i i =1 where M i = the total number of previously marked animals at time i, Ci = the number caught at time i, and Ri = the number of marked animals caught at time i. As an example, suppose we caught and marked 100 animals in our first sample, captured 85 animals (15 marked and 70 unmarked) in a second sample, and then captured 105 animals (25 marked and 80 unmarked) in a third sample. We would then have the following: Table 3.1 Example of Schnabel Index Calculation i 1 2 3 Ci 100 85 105 Ri 0 15 25 New marked 100 70 - Mi 0 100 170 Note that Mi at time 1 is zero; this happens because we start this sampling with no marked animals. For each subsequent time period, Mi is simply the sum of all previous values in the “New marked” column. From the above,...
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