4.1 - D - Analysis with Chi-Squared
When observing organisms in the field, data can be collected using quadrat sampling methods. Quadrats are square sample areas typically determined using a frame (see right photo). This frame is repeatedly moved to random positions in an area and the number and type of organisms present at each. (watch the video to the bottom right to see the method for using quadrats)
When quadrats are used correctly and a large number of sample have been collected, a reliable estimate of population sizes can be calculated. It is important to note, though, that this technique is only suitable for plants an non-motile organisms. If organisms have the potential to move between samplings, then calculations would not be dependable.
If more than one species is counted using quadrats, then it is possible to test for an association between them using chi-squared analysis (see below). This can show whether there is a positive, negative or no association between the presence of each species.
**see pages 207-210 in the book for a great explanation
The Chi-squared test is discussed in Topic 10.2 - D, so please go there for more information. As with genetic traits, this statistical test can be used to discern whether the presences of two species in an area are related.