Mark release recapture
Laura Armstrong
Teacher
Contents
Recall Questions
This topic requires prior knowledge of populations from A-level Biology. You can test your knowledge on this below.
Name three abiotic factors that affect a plant population size.
Temperature, light intensity, and water availability.
How does intraspecific competition affect population size?
It causes population size to fluctuate as individuals of the same species compete for the same limited resources.
What is a population?
All the organisms of one species in a particular area at a given time, who can interbreed to produce fertile offspring.
Topic Explainer Video
What is Mark-Release-Recapture?
MRR is a practical ecological method used to estimate the population size of mobile animals (e.g. insects, small mammals) in a given area at a given time.
Calculation for Population Size
Estimated Population Size
Where:
n₁ = number of individuals captured and marked in the first sample.
n₂ = number of individuals captured in the second sample.
nₘ = number of marked individuals recaptured in the second sample.
This equation assumes the proportion of marked individuals in the second sample reflects their proportion in the entire population.
Example
First capture: 50 moths marked
Second capture: 40 moths captured
Of those, 10 were marked
Estimated population size = 200 moths
No answer provided.
Assumptions of Mark-Release-Recapture
To ensure a representative estimate, the following must be true:
-
The marked individuals mix evenly back into the population. Sufficient time must be allowed between the first and second capture to make sure the captured individuals in the first sample can redistribute fully.
-
There is no immigration or emigration.
-
There is no significant birth or death rate between samples.
-
The mark does not affect survival, for example, it must be non-toxic and must not increase the chance of predation.
-
The mark remains visible and is not lost between captures.
-
The sample sizes must be large.
If any assumption is broken, the estimate could be biased (usually an underestimate or overestimate).
Key Terms
- Population: A group of individuals of the same species in a specific area at a given time that can interbreed to produce fertile offspring.
- Mark-Release-Recapture: A method used to estimate population size of mobile species.
- Closed Population: A population with no immigration, emigration, births, or deaths.
- Estimate: A calculated approximation of population size based on sample data.
- Assumption: A condition that must be true for the calculation to be accurate.
No answer provided.
Exam Tips
Watch out for errors in assumptions!
In 4–6 mark exam questions, you’re often asked to evaluate or justify the reliability of an MRR estimate. Always check whether:
-
Time between samples was sufficient enough to ensure the individuals caught in the first sample mix fully with the rest of the population.
-
The mark type is non-toxic and durable.
-
The area was small enough to be considered closed.
-
The samples caught were large enough.
Mentioning assumptions not being met can be a top-band answer strategy in extended response questions!
No answer provided.
The mark-release-recapture method can be used to estimate the size of a woodlouse population. Explain how. (4 marks)
- Collect sample, mark and release
- Ensure marking is not harmful/ toxic (to woodlice) OR Ensure marking does not affect survival (of woodlice)
- Allow time for woodlice to (randomly) distribute before collecting a second sample
- Population = number in first sample × number in second sample divided by number of marked woodlice in second sample.
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!