Populations in Ecosystems- Investigating Populations

Question 1

Why should samples be random?

Answer 1

To avoid bias

Question 2

How do you take a random sample?

Answer 2

1. Choose an area to sample
2. Pick random coordinates eg. by using a random number generator
3. Use an appropriate sampling technique
4. Repeat the process
5. Estimate the number of individuals

Question 3

Why do we repeat the process?

Answer 3

To reduce the likelihood that the results are down to chance

Question 4

What is a quadrat?

Answer 4

A square frame that is divided into a grid of smaller squares

Question 5

How are quadrats used?

Answer 5

They are placed on the ground at different points within the area you’re investigating and the count the species within each square

Question 6

What is the species frequency?

Answer 6

How often a species is found

Question 7

What can transects be used for?

Answer 7

To find out how plants are distributed across an area

Question 8

What is capture-recapture?

Answer 8

A method used to measure the abundance of animals

Question 9

How does capture-recapture work?

Answer 9

1. Capture a sample of a species using an appropriate technique
2. Mark them in a harmless way
3. Release them back into their habitat
4. Wait some time and take a second sample from the same population
5. Count how many species of the second sample are marked and estimate the total population size

Question 10

How do you estimate the total population size?

Answer 10

Total population size= number caught in 1st sample + number caught in 2nd sample/number marked in 2nd sample

Question 11

What assumptions do you make when using capture-recapture?

Answer 11

• The marked sample has enough time and opportunity to mix back in with the population
• The marking hasn’t affected their chances of survival
• There are no changes in the population size