Acclimation and Acclimatisation

The tolerance limit of a given species is not fixed. Exposure to a near lethal temperature frequently leads to a specific degree of adaptation so that a previously lethal temperature is tolerated. Frequently, the range of thermal tolerance is different for the same species in summer and in winter. A winter animal exhibits tolerance for temperature so low that it is lethal to a summer animal conversely the winter animal is less tolerant to high temperature than a summer animal.

Such changes in the temperature tolerance with climatic changes are called acclimatisation. Likewise effects can be simulated in laboratory experiments by keeping animals for some time at given temperatures. To distinguish the adaptation or adjustment that takes place in laboratory experiments from natural acclimatisation, the response to experimental conditions is often described by the term acclimation. Indeed, animals may show long-term physiological adjustments in response to diverse environmental agents, including (in addition to temperature) humidity, salinity, oxygen supply, photoperiod and food supply to name a few. Furthermore acclimation or acclimatisation can potentially-be exhibited in virtually any physiological property and sometimes in behavioural and morphological properties as well.