Sampling with Quadrats - GCSE Biology Required Practical

Summary

In this informative video, Dr. Acton from Malmesbury Science investigates how to estimate the population size of daisies in a field using quadrat sampling methods. By measuring the field area and applying random sampling, he calculates the average density of daisies, leading to an estimated total population of 4,340. The video also explores how to assess population density variations along a transect, revealing the effects of trampling as a biotic factor on daisy distribution. This engaging exploration highlights essential ecological sampling techniques and their implications for understanding plant populations.

Takeaways

• 🌱 The investigation aims to estimate the population size of daisies in a field using a quadrat.
• 📏 The total area of the field is calculated by measuring its length and width, resulting in 620 square meters.
• 🔢 Random sampling is used to choose 10 quadrat positions, ideally aiming for 5 to 10% of the total area.
• 🌼 When counting daisies, only those that are more than half inside the quadrat are included in the count.
• 📊 The mean average of daisies per meter squared is calculated to estimate the total population.
• ✨ In this example, the total estimated population of daisies is 4,340.
• 📏 A transect line is used to observe how population density varies across different points.
• 🚶‍♂️ Sampling is done at 1-meter intervals along the transect to record the number of organisms.
• 📈 A line graph is plotted to show changes in population density relative to distance from a specific point.
• 🔍 Biotic factors, such as trampling by people, affect the distribution of daisies, while abiotic factors include light intensity and soil pH.

Q & A

What is the main objective of the investigation conducted by Dr. Acton?

The main objective is to estimate the population size of daisies in a field.

What tools does Dr. Acton recommend for estimating the population of daisies?

Dr. Acton recommends using a quadrat and a random number generator to choose random coordinates.

How does Dr. Acton calculate the area of the field?

He measures the length and width of the field using a trundle wheel, approximates it to a rectangle, and multiplies the dimensions to get a total area of 620 square meters.

How many positions does Dr. Acton aim to sample, and how many does he choose to sample today?

He aims to sample around 5 to 10% of the total area, which is about 30 positions, but chooses to sample only 10 today.

What criterion does Dr. Acton use to count a daisy in the quadrat?

A daisy is counted if at least half of it is within the quadrat.

What is the average number of daisies Dr. Acton finds per square meter?

He finds an average of 7 daisies per square meter.

How does Dr. Acton estimate the total population of daisies in the field?

He multiplies the average number of daisies per square meter (7) by the total area of the field (620 square meters), resulting in an estimate of 4,340 daisies.

What is the purpose of using a transect in conjunction with the quadrat?

The transect allows observation of how population density varies between two points within the area.

How does Dr. Acton record the results during the transect sampling?

He places the quadrat at 1-meter intervals along the transect and counts the number of daisies at each position.

What does Dr. Acton's line graph indicate about the population density of daisies?

The graph shows that the number of daisies per square meter increases with distance from the gate, likely due to trampling by people, which is a biotic factor affecting the daisies.