7.4.9 Investigating Species Distribution

Sampling Techniques for Investigating Distribution

1. Random Sampling

• Used to study uniformly distributed species or to avoid bias.
• Steps:
• Use randomly generated coordinates to place quadrats.
• Record the presence, percentage cover, or frequency of species.
• Repeat multiple times for reliability.
• Example: Measuring the percentage cover of grass in a meadow.

2. Systematic Sampling (Transects)

• Used to study how species distribution changes across a gradient (e.g., from a shoreline to a forest).
• Two main types:
• Line Transects: A line is laid, and species touching the line are recorded.
• Belt Transects: Quadrats are placed at regular intervals along the line to measure abundance.
• Example: Investigating how salinity affects plant species from a beach to inland.

Abiotic and Biotic Measurements

• Abiotic factors often influence distribution, so measurements should be taken alongside species counts:
  • Light intensity: Measured using a light meter.
  • Soil pH: Tested with a pH probe or indicator.
  • Temperature: Recorded using a thermometer.
  • Moisture content: Measured using a soil moisture probe.
• Biotic factors such as predation, competition, or grazing intensity should also be considered when explaining distribution patterns.

Data Analysis

• Mean, median, and mode: Used to summarise data.
• Standard deviation: To assess variability within the data.
• Graphs: Scatter graphs or bar charts can show trends.

Statistical Tests

• Use a chi-squared test to determine if the observed distribution significantly differs from expected.
• A Spearman's rank correlation coefficient can assess the strength of a relationship between two variables, such as light intensity and species abundance.