How Big is My Population?
Go to: http://mathbench.umd.edu/modules/env-science_sampling/page01.htm
1: Counting Big Populations: How do scientists estimate the size of a large population?
They take a random sample.
2: Sampling on a grid: To count the dandelions, we'll first create a grid, then use the computer's
random number generator to tell us which grid squares to count. We'll do this 10 times, because,
as you'll see, the counts in the different grid squares will vary a lot. After you count 10 squares,
you'll use the average number per square to estimate the population of the entire lawn.
How many dandelions are there on the grid? 99
3: Scaling it Up: What does it mean that we scaled it up?
To take the samples and scale it to the whole area.
4: Keeping it Random: Why is it important to randomly select segments to count?
Each population needs to have an equal chance of getting selected.
5: When Size Matters: What is the simpliest way to determine the appropriate sample size?
Graph is running average of the samples.
6: Bare Bones Sampling: What is the difference between measuring abundance versus
Presence/absence?
Abundance is the actual number of individuals in a perimeter. While presence/absence requires to determine small areas to sample.
7: Collecting P/A Data: Counting Moss.. How do we estimate sample size?
Randomly pick points in the area to sample. You will then have to estimate the moss's range in percentage.
8: Impervious Surface: How do we estimate impervious surface? Explain.
Use the presence/absence method to pick a bunch of random points then find the percentage that are farms, trees, or houses.
9: Getting Fancy: What are the steps for conducting a simple transect?
10: Try a Transect:
1: Counting Big Populations: How do scientists estimate the size of a large population?
They take a random sample.
2: Sampling on a grid: To count the dandelions, we'll first create a grid, then use the computer's
random number generator to tell us which grid squares to count. We'll do this 10 times, because,
as you'll see, the counts in the different grid squares will vary a lot. After you count 10 squares,
you'll use the average number per square to estimate the population of the entire lawn.
How many dandelions are there on the grid? 99
3: Scaling it Up: What does it mean that we scaled it up?
To take the samples and scale it to the whole area.
4: Keeping it Random: Why is it important to randomly select segments to count?
Each population needs to have an equal chance of getting selected.
5: When Size Matters: What is the simpliest way to determine the appropriate sample size?
Graph is running average of the samples.
6: Bare Bones Sampling: What is the difference between measuring abundance versus
Presence/absence?
Abundance is the actual number of individuals in a perimeter. While presence/absence requires to determine small areas to sample.
7: Collecting P/A Data: Counting Moss.. How do we estimate sample size?
Randomly pick points in the area to sample. You will then have to estimate the moss's range in percentage.
8: Impervious Surface: How do we estimate impervious surface? Explain.
Use the presence/absence method to pick a bunch of random points then find the percentage that are farms, trees, or houses.
9: Getting Fancy: What are the steps for conducting a simple transect?
- Pick a starting point randomly
- Choose a direction randomly
- Lay out a transect using something such as tape measure
- Find the place on the transect to collect some sample data.
- Lay out a frame.
10: Try a Transect:
Summary: Explain what you learned by doing this activity
Throughout this activity I have been able to learn about the three ways to estimate a population. These methods are called abundance, presence/absence, and transect. Abundance estimates a population by actually finding an actual number of individuals in a perimeter. Presence/absence uses random points to sample leading into the estimate by scaling. A transect is sort of like the presence/absence method by more difficult. You have to find a starting point, after you need to find a direction. Both have to be random. By then you need to layout a transect, after you need to place a frame on the place where you want to collect data. These are the three ways to estimate a population.
Throughout this activity I have been able to learn about the three ways to estimate a population. These methods are called abundance, presence/absence, and transect. Abundance estimates a population by actually finding an actual number of individuals in a perimeter. Presence/absence uses random points to sample leading into the estimate by scaling. A transect is sort of like the presence/absence method by more difficult. You have to find a starting point, after you need to find a direction. Both have to be random. By then you need to layout a transect, after you need to place a frame on the place where you want to collect data. These are the three ways to estimate a population.