When we decided to conduct research on crayfish preferences in snails, we asked ourselves whether crayfish eat snails. This was a central question to our research, because if crayfish do not eat snails, they will have no preferences in them. Through our observations, we learned that crayfish do eat snails.
However, this made me wonder whether the crayfish were eating more snails than they would in their natural habitat because they were the only prey available (besides clams). If other species were missing from their diet, perhaps snails would not provide sufficient nutrients to promote increase in length.
To see this relationship more clearly, I created a scatterplot with mass of snails consumed as the input (on the x-axis) and increase in length of each crayfish as the output (on the y-axis).
This produced a string of data points with a very strong positive linear correlation (r^2=0.99581). As the mass of snails consumed increased, so did the increase in length of each crayfish. This graph strongly suggests that snails are an adequate source of nutrients to promote crayfish growth.
N.B. In interpreting this graph, one should take into account that the only prey available were snails and clams. In their natural habitat, crayfish might eat fewer snails and more of other organisms. Thus the mass of snails that they consumed might be less closely associated with their growth.