Capture mark & recapture method pyq , population density estimation pyq , questions on ecology net.

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In an experiment to determine the number of rats in a field, 80 rats were initially captured, marked and released. After one month, 100 rats were captured in the same field, of which 20 were previously marked ones. Based on the above observation, estimated population size of the rats in the field will be:

1. 160

3. 400

2. 200

4. 1600


In order to estimate population size of a fish species in a lake, a researcher captures (100) fish from the lake and marks them with coloured tags. A week later, the researcher returns to the lake and catches 150 fish of the same species and finds that 25 of them are previously tagged ones. Assuming no immigration or emigration occurred, the total population size of the fish species in the lake will be:

1.17

3.600

2.38

4. 860




Given below are the steps to assess thepopulation size of grasshoppers in a givenarea:

A. 4 * n' individuals are collected randomlyfrom the study area in a defined period oftime.

B. The captured individuals are counted,marked and released at the site of collection.Next day, individuals are captured from thesame site for same length of time. Numberof marked (n_{m}) and unmarked (n_{u})individuals are separated and counted.

C. This capture-release and recapture iscontinued till one gets 100% marked individuals.

D. The size of the population (N) isestimated as follows:

N/n = (n_{m} + n_{u})/n_{m}

E. The size of population (N) is estimatedas follows:

N/n = n_{u}/n_{m}

The most appropriate combination of stepsfor estimating population size using mark-recapture method is:

1. A, B and D

2 ^ B * andE

3. A ,B,C and D

4. A, B, C and E



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