Observing Patterns By Ecological Sampling

Core Practical 10 – From Topic 5 (On The Wild Side)

Aim: To carry out a study on the ecology of a habitat, such as using quadrats and transects to determine distribution and abundance of organisms, and measuring abiotic factors appropriate to the habitat.

*The set-up of this practical is at the discretion of your biology teachers as it depends on the environment/habitat that you will be studying. Therefore, the independent, dependent and control variables will be specific to what you are setting out to measure exactly. In general, other abiotic factors such as light, temperature, soil water, humidity, oxygen concentration, pH, aspect, slope angle, etc should be controlled. Similarly, the evaluation points and calculations used will be specific to the habitat you will be studying. Listed below are different types of sampling techniques that can be used:

Random Sampling:

Random sampling is usually used to measure the distribution of an organism in an area which is fairly uniform and very large. Large numbers of samples should be taken by using a quadrat and counting the number of the specific organisms inside the grid. This should be done many times at different points for a more reliable result. In terms of where to place the quadrat, this system involves placing it randomly within the measured area. For example, this can be done by spinning around and throwing at a random moment to remove bias.

Systematic Sampling:

Systematic sampling is when samples are taken at fixed intervals, usually along a line. This normally involves doing transects, where a sampling line is set up across areas where there are clear environmental gradients. For example, you might use a transect to show the changes of plant species as you moved from grassland into woodland, or to investigate the effect on species composition of a pollutant radiating out from a particular source.

Measuring Abundance:

This involves measuring the abundance of an organism and can be done in a number of different ways:

  • Density – presence of organisms per quadrat
  • Frequency – percentage of quadrat squares containing organism
  • Percentage cover – percentage of ground covered with organism in a quadrat (usually for plants)
  • Pitfall trap – to collect invertebrates
  • Sweep net – to collect invertebrates in long grasses
  • Pooter – to collect invertebrates into a container
  • Tullgren funnel – to collect organisms from soil or leaf litter
  • Baermann funnel – to collect living organisms from water

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