The Nazi invasion brought an end to this unique episode in Jewish history. The Jewish urban communities in Yekaterinoslav Guberniya were established on a very small scale alongside the colonies. As time passed and many families found themselves unsuited to rural life, the urban communities were boosted by many who dropped out of the colonies. In effect the original colonists drew in their wake significant numbers of their hometown relatives or neighbours from Lithuania, Latvia and Belarus who constituted the majority in the developing urban communities in Yekaterinoslav. I would point out that there are very few sources about this region's Jewish population.
English books refer briefly to the region.
Most of the other sources are in Russian, particularly a very detailed history of the region which includes many statistical analyses. There is one book in Hebrew devoted to the subject. If further information is of interest I will be happy to expand.