Measuring Population Size and Distribution of Species

Objectives

• Learn how to measure the population size of a common species in a habitat.
• Understand how to use sampling techniques to investigate the effect of a factor on species distribution.
• Understand the importance of these methods in practical biological studies.

Estimating Population Size Using Random Sampling

• Objective: Estimate the total population of daisies in a field using random sampling.
• Method:
  • Use a quadrat to sample areas.
  • Quadrat Size: 0.5 meters x 0.5 meters.
  • Use two 20-meter long tape measures placed at right angles to mark the sampling area.
  • Randomly select two numbers (1-20) to determine quadrat placement within the sampling grid.
  • Count the number of daisies in the quadrat.
  • Repeat for a total of 10 samples.

Calculating Total Population

• Example Calculation:
  • Total area of field: 20m x 20m = 400 square meters.
  • Area sampled: 0.5m x 0.5m x 10 quadrats = 2.5 square meters.
  • Daisies counted in samples: 300.
  • Total Population Equation:
    • Total population size = (Total area / Area sampled) x Number of organisms counted.
    • Example result: 48,000 daisies.

Considerations

• Estimate may not be accurate if quadrat samples don’t represent the whole area.
• To improve accuracy, increase the number of quadrat samples.

Investigating Distribution Using a Transect

• Objective: Investigate how light intensity affects daisy distribution.
• Method:
  • Use a transect line from a tree outward to measure changes in daisy distribution.
  • Place a tape measure from the tree and use a quadrat to count daisies at set intervals.
  • Record light intensity using a light meter or app.
  • Move quadrat along the tape measure and repeat measurements.

Observations

• Potential observation: Increase in daisy numbers further away from the tree.
• Reason:
  • Lower light intensity under the tree affects photosynthesis.
  • Other factors like water and mineral absorption by the tree might also impact distribution.

Practical Considerations

• This is a required practical for students, emphasizing understanding and execution.
• Prepare for questions on this topic in examinations and practical assessments.

Additional Resources

• Revision workbooks available for further practice and understanding.

Note: This guide provides essential understanding and steps to effectively measure and analyze population sizes and their distribution in biological studies.