The point of the three species in Tribus is that they are "rhizobacteria" and don't compete with each other. They are very active in the rhizosphere region of the soil in particular and the three different species help plants uptake different nutrients like Nitrogen, Phosphorus, and potassium...
Tribus is great and the point of the three different species is that they work together as a consortia and the different species help plants uptake different nutrients (i.e. Nitrogen, Phos, Potassium).