Group and community: differences

[AylenM]

Hi!
I was wondering if someone has a response for this question.
Is there any theory about what is group and what is community in SIBER?
What changes at the mathematic level of the calculations one or another classification?
For example, I have the same species, one group historic, and one modern. I put two groups and one community, but now I think, maybe is best to classify into community 1 and community 2? But, group 1 in community 1, and group 2 in community 2? Or group 1 in community 1, and group 1 in community 2?

Any help will be welcome

Thanks!