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Difficulty: MediumPopulation Dynamics and Ecological Sampling

A biology researcher used a 0.5 m20.5\text{ m}^2 quadrat thrown 20 times at random to estimate the population of Mexican sunflower (*Tithonia diversifolia*) in a cashew orchard measuring 500 m2500\text{ m}^2 in Ilorin. If a total of 160 plants were counted across all quadrat throws, what is the estimated total population size of *Tithonia diversifolia* in the orchard?

  1. 8,000 plantsAnswer
  2. B
    160,000 plants
  3. C
    4,000 plants
  4. D
    16 plants

Answer

The estimated total population size of *Tithonia diversifolia* in the orchard is 8,000 plants.
To find the estimated population size, first calculate the total area sampled (20×0.5 m2=10 m220 \times 0.5\text{ m}^2 = 10\text{ m}^2). Next, calculate the population density (160 plants/10 m2=16 plants/m2160\text{ plants} / 10\text{ m}^2 = 16\text{ plants/m}^2). Finally, multiply the density by the total area of the orchard (16 plants/m2×500 m2=8,000 plants16\text{ plants/m}^2 \times 500\text{ m}^2 = 8,000\text{ plants}).

Step-by-Step Solution

1
Calculate the total area sampled by all quadrat throws.
Total sampled area = 20 throws×0.5 m2=10 m220 \text{ throws} \times 0.5\text{ m}^2 = 10\text{ m}^2.
Population density must be calculated relative to the total area examined, not just a single quadrat.
2
Calculate the average population density per square metre.
Population density = 160 plants10 m2=16 plants/m2\frac{160\text{ plants}}{10\text{ m}^2} = 16\text{ plants/m}^2.
Density is determined by dividing total organisms counted by total sampled area.
3
Extrapolate population density to the entire study area.
Estimated total population = 16 plants/m2×500 m2=8,000 plants16\text{ plants/m}^2 \times 500\text{ m}^2 = 8,000\text{ plants}.
Multiplying mean density per unit area by total habitat area yields the estimated total population size.

Key Concept

Population Density and Extrapolation using Quadrat Sampling
Estimated Time:1m 30s
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Topics

Population Dynamics and Ecological Sampling

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