One tube of broth sorts bacteria by the one thing they cannot agree on. Oxygen soaks in from the top and runs out further down. Pick a class, set the jar and the soak depth, and the model works out how fast that microbe can grow at every level. The band you see is the answer.
The tube
Sodium thioglycolate soaks up oxygen. A dash of resazurin dye stays pink where oxygen is left and goes colorless once the broth is reduced. Cells only grow thick enough to cloud the broth at the depths their chemistry allows.