I read some articles on mollusc and fish diet analysis. The formula for percentage frequency of occurrence stated above:
%F0 = Nei/Ne x 100
and percentage numerical abundance :
%NI : Ni/N x 100
especially in mollusc. I want to know how is the calculation for Nei, Ni and N take place, is it an individual organisms count under microscope slide or do we need to used specific device or equipments such as haemocytometer or sedgewick rafter to count the number of the cell per area before we can fill in the Nei, Ni and N in the formula?
Thank you.
If you are counting food items, then both formulas will give you exactly the same result. Now, the real catch is what we mean when we say abundance. Is it the amount of events of finding a given food item? Is it how much biomass of a given food item a mollusc is ingesting? Is it a standardized methodology of counting? This is something that you have to think about.
Every time you want to find out how much of something is ingested we need to think about this: A count is meaningless in its nature. The count is only meaningful if you scale it to the representation of the total. Here is where the percentage comes into play. It will always capture the proportional amount of something. Therefore, we will always do it as: part/total X 100.
Now for your methods, I don't know much about molluscs but perhaps you could put the contents of the crop into a slide. The slide is now your sample. The Total is the total count of food items. The parts are the frequency of a given item. The same logic apply if you decide to quantify abundance using biomass (which is perhaps better but way more difficult to do), but the counts will be replaced with weights.
Thank you very much for your sharing sir. That was indeed a great explanation and I come to realise some important points that I'd might missed out.
I get a better picture on what to be considered before the counting take place. I got confused on how the N values were counted. Previous researches might have used counter or special devices to get the numbers of organisms, by then using certain formulas (like you said, part/ total x 100) can help to estimate the total numbers of organisms/food per slide.
I really appreciate the help! That was awesome.
Kindly check https://www.researchgate.net/publication/330621031_Stomach_Content_Analysis_Techniques_in_Fishes
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