Worth reading some of the previous posts on here.
Communities are nothing to do with ethnicity regions determined through laboratory examination of your DNA. They are derived in a similar way to Thrulines by Ancestry trawling through your tree and those of your DNA matches, looking for common areas of residence shown in the trees of autosomally related ancestors.
Ethnicity is derived from laboratory examination of your DNA. However it is important to recognise that the percentages shown are ESTIMATES and subject to constant reassessment and verification.
A particular percentage cannot be used to determine how many generations back a particular ethnicity is linked. That's not how it works. It is completely different to autosomal relative matching and less precise.
Ancestry say that ethnicity estimates are indicative of ethnicity derived between 500 to several thousand years ago, so generally well beyond the reach of autosomal matching and documentary research into ancestral lineage.
The "headline" ethnicity percentages shown are an overall estimate representing a range of probability for each region. If you drill down into each regional estimate in your results you will find that the actual range may vary widely from the headline percentage shown. For a 3% headline estimate and similar low figures for instance, it isn't at all unusual for the actual estimated range to include a probability of 0% - in other words the possibility that there may actually be no relationship to that region at all.