Biology – Biodiversity | e-Consult

A mark-release-recapture (MRR) technique can be used to estimate the abundance of a species of insect. This involves capturing a sample of insects, marking them, releasing them back into the population, and then subsequently recapturing a sample of insects. The proportion of marked insects in the second sample is then used to estimate the total population size.

Equipment Required:

• Insect net (e.g., a sweep net or a gill net)
• Marking material (e.g., insect-safe paint, colored tags, or a chemical marker)
• A recording sheet to record the number of insects captured, marked, and recaptured.
• A suitable habitat for releasing the marked insects.

Procedure:

1. Capture the initial sample: Use an insect net to capture a sample of the insect population. Record the number of insects captured (m).
2. Mark the insects: Carefully mark each insect with a unique identifier. Ensure the marking is durable and does not harm the insect.
3. Release the marked insects: Release the marked insects back into the population in the same habitat where they were captured. Ensure they have a chance to mix back into the population.
4. Recapture the insects: After a suitable time period (allowing for mixing), use the insect net to capture a second sample of the insect population. Record the number of insects captured (n).
5. Record the number of marked insects in the second sample: Count the number of marked insects in the second sample. This is the number of recaptured marked insects (m).

Data Analysis:

The estimated population size (N) is calculated using the Lincoln Index: N = m / n. This formula estimates the total population size based on the proportion of marked insects in the second sample.

Potential Sources of Error:

• Marking effects: The marking process may affect the survival or behaviour of the insects, leading to an underestimation or overestimation of the population size. The marking material must be carefully chosen to minimize any negative effects.
• Mark loss: The marks may be lost over time due to weathering, abrasion, or predation. This will lead to an overestimation of the population size.
• Unequal catchability: Not all insects have an equal chance of being captured in either sample. Some insects may be more likely to be captured than others (e.g., due to differences in behaviour or habitat preference).
• Closed population assumption: The assumption that the population is closed (no births, deaths, immigration, or emigration) may not be valid, especially if the time interval between the two sampling periods is long.
• Random distribution: The assumption that marked individuals are randomly distributed throughout the population may not be true. If marked individuals tend to aggregate, the Lincoln Index will overestimate the population size.