# ecosystems Watch

1. 'To work out how many are needed, ecologists carry out a pilot study. They take random samples from across the habitat and make a cumulative frequency table, like the one shown in table 1. They then plot cumulative frequency against quadrat number. The point where the curve levels off tells them the minimum number of quadrats to use...'

Table 1:

So what are they plotting exactly? They'll probably plot 'number of quadrats' on the x axis, but what are they plotting on the y axis (,'number of new species found in this quadrat' or 'total number of different species found'?
2. The ecologists take random samples from across the habitat to produce table 1. Then I think what they are referring to is plotting 'Quadrat number' (x-axis), like you said, against 'Total Number of different species found' and then you can identify from the graph, the point at which the total number of different species found stops increasing. In this case, at quadrat number 11, the value is 28 and does not change from this point, therefore indicating that there is no need to use more than 11 quadrats, since the same results will be found. I tried uploading a graph, which should illustrate what the graph would look like.
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3. (Original post by Rhodopsin94)
The ecologists take random samples from across the habitat to produce table 1. Then I think what they are referring to is plotting 'Quadrat number' (x-axis), like you said, against 'Total Number of different species found' and then you can identify from the graph, the point at which the total number of different species found stops increasing. In this case, at quadrat number 11, the value is 28 and does not change from this point, therefore indicating that there is no need to use more than 11 quadrats, since the same results will be found. I tried uploading a graph, which should illustrate what the graph would look like.
Thank you so much!
4. No problem

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Updated: April 2, 2013
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