Figure 3.

The resistance or ‘quasi-stability’ of a community reflects its capacity to resist change in structure in response to a disturbance event. Ecosystem disturbances can occur at varying intensities and frequencies or durations, indicated here on the y-axis (magnitude or intensity) and x-axis (frequency or duration), respectively. Panels (A) and (B) represent two communities with different levels of resistance. The lighter portion in the bottom left-hand portion of each space represents an ecosystem’s quasi-stable state in which changes may occur to the community structure without pushing it into a ‘disturbed’ state. The darker portion in the upper right represents the disturbed ecosystem. Circles surrounded by dashed lines with an “i” inside represent various initial states of an ecosystem, and circles with solid lines and “f” inside represent the final state following a disturbance event. Some disturbances may push the ecosystem to another point within its quasi-stable space (e.g., f₁ in [A]; f₁ and f₂ in [B]) whereas some disturbances may be great enough to push the community into a ‘disturbed’ state (e.g., f₂ and f₃ in [A]; f₃ in [B]). Communities that differ in species composition are likely to have different degrees of resistance. In our example, communities A and B experience the same disturbances, but in (A) disturbance events 2 and 3 push the community into a disturbed state whereas in (B) only disturbance event 3 is strong enough to disturb the ecosystem from its quasi-stable state.