Free Measuring Distribution OCR A Level Biology revision notes – covering specification points 6.3.1(ei) and 6.3.1(eii).
Measuring Distribution
Distribution is the range of locations at which the individual organisms of a species can be found across a habitat.
Distribution can be determined using systematic sampling to take measurements along a transect whilst taking abiotic measurements at the same locations, producing paired data that may show a correlation between an abiotic factor and the abundance of a species.
Systematic Sampling
Systematic sampling can make use of belt transects or line transects:
- Belt transects use quadrats placed at set intervals along the transect line to record the abundance* of each species.
- Line transects only record the species touching the transect line at set intervals to produce a quicker, but less representative, distribution of each species.
*Or coverage.
The table below outlines examples of investigations that would use systematic sampling:
| Investigation | Approach | Observation | Results |
|---|---|---|---|
| Investigating seaweed distribution up a rocky shore | Use systematic sampling by placing a line transect from the low-tide to the high-tide mark, recording the species touching the tape at set intervals and measuring the height below high-tide. | Different seaweed species occur at different heights up the shore. | Species occurrence is plotted against submersion depth. |
| Investigating plant abundance along a light gradient from a woodland edge | Use systematic sampling by placing 1 m2 quadrats at 5 m intervals along a belt transect from the woodland edge into a field, recording the abundance of each species and the light intensity. | Light-demanding species in the open ground replace shade-tolerant species near the woodland edge. | The abundance of each species is plotted against light intensity. The abundance of each species may also be plotted against distance on a kite diagram. |