G&E: Investigating Populations

Question 1

What can be used to investigate non-motile or slow-moving organisms?

Answer 1

Quadrats and transects

Question 2

Mark-release-recapture

Answer 2

Technique that measures the abundance of motile species

Question 3

Describe how mark-release-recapture is performed:

Answer 3

• Capture a sample of a species using an appropriate technique.
• Mark them in a harmless way.
• Release them back into their habitat.
• Wait an appropriate amount of time, then take a second sample from the same population.
• Count how many of the second sample are marked.
• Use equation to estimate the total population size.

Question 4

What equation is needed for the mark-release-recapture technique?

Answer 4

Total population size = (number caught in 1st sample x number caught in 2nd sample) / number marked in 2nd sample.

Question 5

What assumptions do you make when using the mark-release-recapture method?

Answer 5

• Marked sample has had enough time and opportunity to mix back in with population.
• Marking hasn’t affected the individual’s chances of survival, eg. more visible to predators, and the marking itself is still visible.
• No changes in population size due to births, deaths and migrations during period of study.