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Just a note

Extremely few studies have estimated the total number of species, of all phyla, in a natural biological community. Attempting to quantify the total genetic diversity of a community is still more difficult - if for no other reason than, to be in any way meaningful, such a measure needs to allow for how different each genome is - rather than merely counting how many there are.

This latter point becomes explicit when we realise that even cloned organisms may not have identical genomes - simply because their DNA replicases are not wholly error free. Mutagens and recombination ensure that few individuals of any naturally-reproducing species are genetically identical. In which case, if we did not allow for the degree of genetic difference, genetic diversity would mainly be a function of the number of individuals in the community. If all phyla were included, the most diverse community would probably be whichever has the most bacteria!

Intuitively, you might assume that using phenotypic (shape and form) differences, rather than genetic ones, is an obvious alternative - partly because it should reflect the diversity of habitats. Unfortunately these sorts of measures are even more difficult to quantify.

Counting the number of species in a given phylum simplifies the problem, but it still makes no allowance for the degree of taxonomic difference between each species - nor how many 'species' are really subspecies or merely local variants.