Aquascope Facts

The effects of manipulation

Quite often, one has to also control if manipulation within the experimental areas has effected any changes other than what is stipulated in the hypothesis. Besides the expected effect that the number of supposed competitors decrease in numbers, other changes and disturbances can occur when the mussels are removed from a sandbottom. Manipulative disturbances can on their own affect survival within the experimental areas. Therefore, controls are needed where mussels are first removed and then replaced so the same effect is obtained as in the experimental areas, but without actually changing competition between the competitors. Other controls could also be necessary. It is only with the help of controls that we can see the effects of natural changes and unwanted manipulation, and be able to separate these changes from those prescribed in the hypothesis.


Finally, an experiment must be repeated, or with a scientific term replicated. Several experimental and control areas are needed over the area that is to be studied. This is necessary as there can exist many natural factors that effect the number of mussels on different areas of the beach. During the period that the experiment is in progress, many factors can change and can vary in different areas.
    Suppose that we have only one experiment area and one control area. When we conclude the experiment and see that the conditions between the different species of mussels have changed, we will not know why. These changes can either be due to changes in competition or changes in natural conditions within the experimental area, compared to the control area. Such a natural change could for instance be when an influx of available food has occured at that particular part of the seabottom where the experimental area is situated compared to the control area.
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