Biology Population Measurement Techniques

What is the primary purpose of using quadrats in population sampling?

Which of the following is a limitation of the quadrat sampling method?

What is the first step in the mark-recapture method of population estimation?

In the mark-recapture method, what does the proportion of marked individuals in the second sample represent?

Using the mark-recapture formula, if 20 individuals are marked (M) and 50 individuals are recaptured (m), what is the population size estimate (N) if the second sample size (n) is 200?

In the provided example, if 48 polar bears are marked and 6 out of 30 recaptured are marked, what is the calculated population size?

Why might mark-recapture sampling be preferred over quadrat sampling for certain organisms?

Which aspect is NOT a factor considered when using quadrat sampling?

Measuring Population Characteristics

Estimating population size is often difficult, so biologists use sampling techniques.

Sampling Techniques

Quadrat Sampling (for stationary organisms):
- A quadrat (a frame of a specific size) is placed randomly within a habitat.
- The number of individuals within the quadrat is counted.
- This count is used to estimate the total population size.
Limitations of quadrat sampling:
- Ineffective for clumped populations. If the quadrat falls within a clump, it will overestimate the population; if it falls between clumps, it will underestimate.
Mark-Recapture Sampling (for mobile organisms):
- A group of organisms is captured, tagged, and released.
- After a period of time, a second sample is taken.
- The proportion of marked organisms in the second sample is used to estimate the total population size.
Rationale: If the proportion of marked individuals in the second sample reflects the proportion of marked individuals in the whole population, the total population size can be estimated.
Mark-Recapture Formula: N = (M * n) / m Where:
N = Estimated population size
M = Number of individuals marked in the first sample
n = Total number of individuals in the second sample
m = Number of marked individuals in the second sample

Example Calculation

Example using polar bears:
48 polar bears marked initially
30 polar bears captured in the second sample
6 of the bears in the second sample were marked
Estimated population size: (48 * 30) / 6 = 240

Assumptions of Mark-Recapture Sampling

All individuals have an equal chance of being captured.
The ratio of marked to unmarked individuals stays constant during the study period. This means tagging does not affect survival rates.
Population size remains constant during the study.

Explore the various methods used by biologists to estimate population sizes, including quadrat and mark-recapture sampling techniques. This quiz covers the rationale behind these methods, their applications, and limitations. Test your understanding of sampling in ecological studies.