  In general, biological experience suggests that all populations regulate their sizes, that is, they show self-regulation. Theoretical exploration of models has made it clear that a wide variety of mechanisms can lead to such self-regulation but it is usually unclear which models are more plausible than others thanks to the typical formalization indeterminacy of the field. Moreover, the precise mechanisms that are playing regulative roles in individual cases are often very hard to determine in the field, a classic case of partial observability. Even parameters such as the intrinsic growth rate and carrying capacity are unusually difficult to estimate precisely.