In physics there is an interesting theorem that says that if a physical system behaves the same under some rotation of symmetry in the system then there will be a physical value that is conserved. So for instance if a physical system is rotationally invariant then it will conserve angular momentum. This theorem is called Noether’s theorem.
In an open collaboration if you rotate people in and out of a project the project will still generally behave the same. E.g. in Wikipedia if different people switch into the project the writing of the encyclopedia should still continue be the same. In a hierarchically run project when you switch in different people to become CEO, managers etc the project will probably start to run differently. So in the case of open collaborations there should be some social phenomena that is conserved. In this case it would be the rate of people flowing into and out of the project should stay relatively stable. In a hierarchically run project the rate of people flowing in and out is not as constant, it might depend on the CEO’s personal predilections more. This is all assuming the environmental conditions stay the same, if conditions change then projects will change there people flow rate.