An ecological crisis occurs when the environment of a species or a population changes in a way that destablizes its continued survival. There are many possible causes of such crises:

• It may be that the environment quality degrades compared to the species' needs, after a change of abiotic ecological factor (for example, an increase of temperature, less significant rainfalls).
• It may be that the environment becomes unfavourable for the survival of a species (or a population) due to an increase pressure of predation (for example overfishing).
• Lastly, it may be that the situation becomes unfavourable to the quality of life of the species (or the population) due to raise in the number of individuals (overpopulation).

The evolutionary theory of punctuated equilibrium sees infrequent ecological crises as a potential driver of rapid evolution.