An ecology student investigated the population of spear grass (*Imperata cylindrica*) on a… — JAMB UTME

An ecology student investigated the population of spear grass (*Imperata cylindrica*) on a $400\text{ m}^2$ plot in Jos, Plateau State. A rectangular quadrat measuring $1.0\text{ m} \times 0.5\text{ m}$ was thrown randomly 16 times across the plot, yielding a total count of 120 spear grass plants. What is the estimated population density of spear grass in $\text{plants/m}^2$ ?

A
$7.5\text{ plants/m}^2$
$15.0\text{ plants/m}^2$ Answer
C
$0.3\text{ plants/m}^2$
D
$240.0\text{ plants/m}^2$

Answer

15.0\text{ plants/m}^2

The population density is defined as the total number of individuals of a species per unit area sampled. The area of one quadrat is

1.0\text{ m} \times 0.5\text{ m} = 0.5\text{ m}^2

. Sampling 16 times gives a total sampled area of

16 \times 0.5\text{ m}^2 = 8.0\text{ m}^2

. Dividing the total count of 120 plants by

8.0\text{ m}^2

yields

15.0\text{ plants/m}^2

Step-by-Step Solution

Calculate the area of a single quadrat frame

\text{Area of 1 quadrat} = 1.0\text{ m} \times 0.5\text{ m} = 0.5\text{ m}^2

Determines the sampling surface area covered by one throw.

Calculate the total area sampled across all quadrat throws

\text{Total sampled area} = 16 \text{ throws} \times 0.5\text{ m}^2 = 8.0\text{ m}^2

Finds the total ground space inspected during the field survey.

Calculate the population density of spear grass per square metre

\text{Population Density} = \frac{\text{Total plant count}}{\text{Total sampled area}} = \frac{120\text{ plants}}{8.0\text{ m}^2} = 15.0\text{ plants/m}^2

Determines average number of organisms per unit area.

Key Concept

Quadrat Population Density Calculation

Estimated Time:1m 30s

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