Currently, it seems that species groups are tied back to the Species table. I think it would provide a lot of flexibility to users if groups could be assigned at the calibration level (CalibrationSpecies), since different properties, owners, and regions all group the same species differently. Even allowing multiple groups would be helpful, as sometimes operations, appraisers, and financial groups want different groupings.
Species group has been moved to species calibrations in the upcoming version 2022.3.8. This means each species can belong to a different group in different calibrations.