Fig. 2. The paradigmatic difference between engineering and ecological resilience can be illustrated by the ball-and-cup heuristic (Scheffer et al. 1993, Walker et al. 2004). The cup represents the region in the state space or "basin of attraction", in which the system tends to remain, and includes all possible values of system variables of interest. The ball represents the state of the system at any given time. The engineering resilience concept assumes only one regime, hence only one possible basin of attraction; and the very bottom of the basin represents the ideal stable state. The ecological resilience concept assumes multiple regimes, hence more than one basin of attraction. The system may move about within the basin, never settling at the bottom; it may also cross a threshold and settle in a new basin of attraction. The notion of engineering resilience is concerned with whether the system can remain at the bottom of the basin; while the notion of ecological resilience is concerned with whether the system can remain within the current basin (Holling 1996).