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Difficulty: HardPopulation Dynamics and Ecological Sampling

An ecology student investigated the population of *Tridax procumbens* in a cassava farmland in Ogun State using a 0.5 m×0.5 m0.5\text{ m} \times 0.5\text{ m} quadrat frame. Across 10 random quadrat throws, the total number of *Tridax procumbens* plants counted was 80. What is the estimated population density of *Tridax procumbens* per square metre (m−2\text{m}^{-2}) in the farmland?

  1. A
    8 plants m−28\text{ plants m}^{-2}
  2. 32 plants m−232\text{ plants m}^{-2}Answer
  3. C
    160 plants m−2160\text{ plants m}^{-2}
  4. D
    320 plants m−2320\text{ plants m}^{-2}

Answer

The population density of *Tridax procumbens* is 32 plants m−232\text{ plants m}^{-2}.
The area of one quadrat frame is 0.5 m×0.5 m=0.25 m20.5\text{ m} \times 0.5\text{ m} = 0.25\text{ m}^2. Across 10 throws, the total area sampled is 10×0.25 m2=2.5 m210 \times 0.25\text{ m}^2 = 2.5\text{ m}^2. Dividing the total number of plants counted (80) by the total sampled area (2.5 m22.5\text{ m}^2) yields an accurate population density of 32 plants m−232\text{ plants m}^{-2}.

Step-by-Step Solution

1
Calculate the area of a single quadrat frame.
Area of 1 quadrat=0.5 m×0.5 m=0.25 m2\text{Area of 1 quadrat} = 0.5\text{ m} \times 0.5\text{ m} = 0.25\text{ m}^2
Determines the spatial coverage of one quadrat throw.
2
Calculate the total area sampled across all quadrat throws.
Total sampled area=10×0.25 m2=2.5 m2\text{Total sampled area} = 10 \times 0.25\text{ m}^2 = 2.5\text{ m}^2
Accounting for all 10 sampling units used during field sampling.
3
Divide the total count of organisms by the total sampled area.
Population Density=80 plants2.5 m2=32 plants m−2\text{Population Density} = \frac{80\text{ plants}}{2.5\text{ m}^2} = 32\text{ plants m}^{-2}
Population density is defined as the number of individuals of a species per unit area.

Key Concept

Quadrat Sampling and Population Density Calculation
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Topics

Population Dynamics and Ecological Sampling

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