2.1F Population abundance estimation Notes

1. Estimating population abundance is essential for understanding the distribution and health of species within an ecosystem.
2. To do this, scientists use various sampling techniques depending on the characteristics of the area and species being studied.
3. These techniques include random sampling, systematic sampling, and transect sampling.

Sampling Principles

1. The choice of sampling method depends on:
   1. The mobility and distribution of organisms
   2. The size and accessibility of the study area
   3. The precision required for the investigation
   4. The available time, resources, and equipment
2. The three most commonly used methods are random sampling, systematic sampling, and transect sampling.

Random Sampling

1. In random sampling, every point or location within the study area has an equal chance of being selected.
2. This method avoids researcher bias and is most effective when the population is uniformly distributed.

Procedure

1. Mark the study area using two tape measures to form a grid (e.g., 10 m × 10 m).
2. Use a random number generator to select coordinates for sampling points.
3. Place a quadrat (a square frame, usually 0.25 m²–1 m²) at each coordinate.
4. Record all individuals within the quadrat or estimate their percentage cover.

Advantages

1. Reduces human bias and ensures representative data.
2. Useful for homogeneous habitats like grasslands or meadows.

Limitations

1. Inefficient for clumped or patchy populations.
2. May miss rare species if the distribution is uneven.

Systematic Sampling

1. Systematic sampling involves selecting samples at regular intervals along a grid or line.
2. It is appropriate when there is a clear environmental pattern or gradient, such as changes in soil moisture, light intensity, or altitude.

Procedure

1. Establish a baseline and place sampling points at equal distances (e.g., every 5 m).
2. Collect data at each point using quadrats or other methods.

Advantages

1. Ensures that samples cover the entire area evenly.
2. Detects spatial patterns and population gradients effectively.

Limitations

1. May introduce bias if the pattern of the species coincides with the sampling interval.
2. Not truly random, which may reduce statistical accuracy.

Transect Sampling

1. Transect sampling involves laying a line (transect) across the study area and taking samples at regular intervals along it.
2. This method is particularly useful for studying changes across environmental gradients.

Types of Transects

1. Line transect:
   Record species that touch the line at regular points.
2. Belt transect:
   Place quadrats continuously or at intervals along the line to record species within a given strip width.
3. Interrupted transect:
   Place quadrats at regular gaps (e.g., every 10 m) rather than continuously.

Applications

1. Examining zonation patterns (e.g., rocky shore species distribution from low tide to high tide).
2. Studying succession or the effect of human disturbance.

Advantages

1. Provides data on species change along environmental gradients.
2. Allows simultaneous recording of biotic and abiotic factors (e.g., light, soil type, salinity).

Limitations

1. Time-intensive.
2. May not account for microhabitat variations if only one transect is used.

Quadrat Sampling Technique

Materials Needed

1. Quadrat (frame of known area, e.g., 1 m²)
2. Measuring tapes and stakes