Question

1. Describe and state the assumptions and disadvantages of the mark-recapture technique used to quantify population size and density.

Answer 1

The mark-recapture technique is one of the most popular techniques to estimate population size. This technique is widely used to determine the population size where counting each and every individual is practically impossible. The basic idea behind this technique is to capture a small population of the organism, mark them harmlessly, and then again release them back into the population. This is repeated many times and the number of marked individuals is recorded.

In a small population, it is more likely to recapture the marked individual whereas in a large population it is difficult.

N=(M x C)/R

• N= Number of individuals in the population
• M=Number of individuals that have been captured and marked.
• C=Total number of individuals captured for the second time with a mark or without a mark.
• R=Total number of individuals that are recaptured with a mark.

4 common assumption

1. The technique used for marking must not harm the individual either in behavior, life expectancy, survival and predation. The mark should not be washed off or lost.

2. Sufficient time should be there between the initial marking period and recapture periods that individuals of the population can be randomly dispersed in the population.

3. The chances of each individual to be caught is equal and constant for the marking and recapturing period. It means that catching the marked individual should neither be easy nor be difficult.

4. There must be no immigration or emigration of an individual in the population. This means that the population should be closed.

Disadvantages

1. The accuracy of the result depends upon the population size. As stated above it is more likely to recapture an individual in a small population, than compared to a large population.
2. The assumption of the closed population is difficult to achieve.
3. A large population requires extensive and long term efforts due to low recapture rates.
4. Time-consuming and costly approach.