Estimating Species Population

Overview

• Multiple methods exist for counting or estimating populations of species.
• Choice of method depends on available resources and type of species.

Direct Counting Methods

• Complete Counts: Counting all individuals in an area.
  • Often aided by aerial flyovers or photography.
  • Rarely used due to high resource and personnel demands.
• Drive Approach: Individuals walk across an area to count organisms.

Indirect and Estimated Counts

• Common due to resource constraints.

Key Estimation Methods

1. Mark Recapture Method

• Used for mobile species; also called capture-recapture method.
• Process:
  1. Capture animals using traps or other methods.
  2. Mark animals with a tag or band.
  3. Release marked animals back into the environment.
  4. Capture a new sample and note marked individuals.
• Ratio of marked to unmarked individuals estimates total population size.

2. Quadrant Sampling Method

• Suitable for species with limited mobility (e.g., plants, snails).
• Process:
  1. Use a quadrant to randomly select areas for counting organisms.
  2. Count organisms within the quadrant.
  3. Extrapolate data to larger areas based on quadrant size.
• Example: Counting organisms in a 1 square meter quadrant can be applied to a larger area.

3. Transect Sampling Method

• Involves drawing lines across a study area.
• Process:
  1. Walk along transect lines and count observed organisms.
  2. Record distances of organisms from transect line.
• Data used to estimate total population based on observed species along each transect.

Conclusion

• Various methods exist for population estimation; the discussed methods are commonly used.