  Stability turns out to be even more difficult to  define.[39]  At one extreme, stability can be defined to require that a community be truly in equilibrium: it does not change in either its composition (the abundances of every component)or in the interactions among these components. At the practical level, this definition faces the problem of vacuous scope: almost no natural community satisfies such a strict requirement of equilibrium. Moreover, almost every community experiences significant disturbances. With this in mind, stability has been variously explicated using a system's response to disturbances or its tendency not to change beyond specified limits even in the absence of disturbance. Boxes 3 and 4 (see below) list some of the definitions of stability that have been in vogue and how they may be measured in the  field.[40]