A scientist is conducting surveys in the tropics of rare lizards. They used the

Question

A scientist is conducting surveys in the tropics of rare lizards. They used the mark-and-recapture method to determine their population size. Over a period of 4 months they initially collected and marked 553 lizards. A year later, they returned and collected 345 lizards, of which 123 were marked. a. Calculate the estimated population size. b. Describe the assumptions of the method used to calculate the population size. If these species have a type 2 survival curve and a life expectancy of 5 years, would you over or under estimate their population?

Explanation / Answer

A) Formula for estimation in marked recapture test

Marked recapturs / Total in second sample = Marked initially / total population size

total population size = Marked initially X Total in second sample / Marked recaptures

= 553 X 345 / 123

   = 1551 lizards

B) Following assumptions should be met for the accuracy of marked recapture estimation

    1) Population should be closed, that means there should be equal no. of deaths and births. There should not be any immigration or emigration for the population, which might upset the balance.

    2) Probability of marked individuals to be captured should not change. Marking method should not make them easy as well as difficult to capture them.

    3) Proper time must be given, to the marked individuals to mix completely into population.

    4) They should not lose their marks, which will lead to the overestimation of the population.

C) In type 2 survival curve, death rate is constant at any age. As the assumption 1 of equal number of deaths and births of individuals is happening, there is no over or under estimation of population in this method.

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