Biostasis is the ability of an organism to tolerate environmental changes without having to actively adapt to them. The word is also used as a synonym for cryostasis or cryonics. It is found in organisms that live in habitats that may encounter unfavourable living conditions (ie. drought, freezing, a change in pH, pressue, or temperature). Insects undergo diapause, which allows them to survive winter and other events. Diapause may be obligatory (required for the insect to survive) or facultative (the insect is able to undergo change before the initiating event arrives).