  It is the third criterion that is often called into question by Shaffer's classification of stochasticity primarily because of formalization indeterminacy. Consider some small reptile that fails to breed because a flood creates a barrier across its habitat that it cannot cross and there are no available mates on its side of the barrier. Is this environmental or demographic stochasticity? On the one hand, it is obviously environmental because floods are precisely the type of mechanism by which environmental stochasticity is expressed. On the other hand, it is equally obviously demographic because the failure to reproduce is due to the chance unavailability of a mate on the appropriate side of the barrier. Ultimately, as will be discussed below in some detail, whether this is a case of demographic or environmental stochasticity depends on how it is modeled. There is an important philosophical lesson here: especially when a new discipline is being formed, the structure of the phenomena—how they are distinguished and classified—are in part determined by the models used to represent them. Consequently, classification is not theoretically innocent. This is as true in ecology as in any other scientific context.