NECO 2002 Biology · Question 36

Use the data to answer this question A class of 40 set out to determine the population of lizards in a bound…

Question

Use the data to answer this question A class of 40 set out to determine the population of lizards in a bound field measuring 200 metres by 100 metres using the capture-recapture method. In their first outing, the students captured a total of 360 lizards all of which were marked with indelible ink and then released back into the field. After a one week interval the students went back into the field and caught a total of 250 lizards out of which 150 bore the indelible ink mark. The population density of the lizards in the field is?

A.0.003 per m 2
B.0.03 per m 2
C.3 per m 2
D.4 per m 2
E.6 per m 2

Answer: B. 0.03 per m 2

Explanation written with AI and checked against the answer key

Analyze the question: We use the capture-recapture (Lincoln-Petersen) method to estimate the population, then divide by the area to get the density.

Concept: Population estimate N = (number marked in first catch × total in second catch) ÷ number of marked recaptured

Step 1: Estimate the population

First catch (marked) = 360
Second catch = 250
Marked in second catch = 150

N = (360 × 250) ÷ 150 = 90,000 ÷ 150 = 600 lizards

Step 2: Find the area Area = 200 m × 100 m = 20,000 m²

Step 3: Population density Density = 600 ÷ 20,000 = 0.03 per m²

Tip: In capture-recapture questions, always do the two steps separately: (1) find the population with N = (M × C) ÷ R, then (2) divide by the area if density is asked. Option A (0.003) is a common trap from slipping a decimal place. Check your zeros when dividing by 20,000.

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