Hi everyone!
I have a technical question here related to ecological distance indices. I have calculated a Bray-Curtis dissimilarity matrix for several sites using the raw abundance value of species. However, I would like to know what is the contribution of the total variation in abundance in the calculation of this matrix. In fact, Bray Curtis indices is both influenced by variation in abundance AND variation in species composition per se. That is, if two sites have the same species composition (I'm talking about same PROPORTION of species) but different abundance, the Bray Curtis index will be very different. Let say I have 5 species. In site 1 species abundance for species 1 to 5 is 1,2 ,3 4, and 5 individuals respectively. At site 2, species abundance is 10, 20, 30, 40 , 50 respectively. So, species composition per se is similar but abundance is 10x higher at site 2. Using raw abundance value, The BRay-Curtis index would be roughly 0.81 (let's name it BCraw). Using proportions, it would be 0 (let's name it BCprop). So, only the variation in total abundance here is impacting the calculation of the BRay Curtis index using raw abundance, not species COMPOSITION per se. Soooo....
In order to estimate the "contribution" of total abundance to the Bray-Curtis value calculated using raw species abundance, would it be legit to calculate BCraw - BCprop ?
Thanks a lot!
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