Acclimatization, or acclimation
It is the process in which an individual organism adjusting to a gradual change in its environment, such as a change in temperature, humidity, photoperiod, or pH, allowing it to maintain performance across a range of environmental conditions. Acclimatization occurs in a short period of time from days to weeks, and within the organism's lifetime.
This may be a discrete occurrence or may instead represent part of a periodic cycle, such as a mammal shedding heavy winter fur in favor of a lighter summer coat. Organisms can adjust their morphological, behavioral, physical, and/or biochemical traits in response to changes in their environment. While the capacity to acclimate to novel environments has been well documented in thousands of species, researchers still know very little about how and why organisms acclimate the way that they do.
Biochemical changes
In order to maintain performance across a range of environmental conditions, there are several strategies organisms use to acclimate. In response to changes in temperature, organisms can change the biochemistry of cell membranes making them more fluid in cold temperatures and less fluid in warm temperatures by increasing the number of membrane proteins. Organisms may also express specific proteins called heat shock proteins that may act as molecular chaperons and help the cell maintain function under periods of extreme stress. It has been shown, that organisms which are acclimated to high or low temperatures display relatively high resting levels of heat shock proteins so that when they are exposed to even more extreme temperatures the proteins are readily available. Expression of heat shock proteins and regulation of membrane fluidity are just two of many biochemical methods organisms use to acclimate to novel environments. Note: acclimation and acclimatization are two very different terms that are not interchangeable. Acclimation is used under laboratory conditions, while acclimatization is "in the field" or in nature.
Morphological
Organisms are able to change several characteristics relating to their morphology in order to maintain performance in novel environments. Examples may include changing of skin color or pattern to allow for efficient thermoregulation, or a change in body size of offspring as a result of low food levels in the ecosystem.
The degree to which organisms are able to acclimate is dictated by their phenotypic plasticity or the ability of an organism to change certain traits. Recent research in the study of acclimation capacity has focused more heavily on the evolution of phenotypic plasticity rather than acclimation responses. Scientists believe that when they understand more about how organisms evolved the capacity to acclimate, they will better understand acclimation.
Examples
Plants
Many plants, such as maple trees, irises, and tomatoes, can survive freezing temperatures if the temperature gradually drops lower and lower each night over a period of days or weeks. The same drop might kill them if it occurred suddenly. Studies have shown that tomato plants that were acclimated to higher temperature over several days were more efficient at photosynthesis at relatively high temperatures than were plants that were not allowed to acclimate.
Animals
Animals acclimatize in many ways. Sheep grow very thick wool in cold, damp climates. Fish are able to adjust only gradually to changes in water temperature and quality. Tropical fish sold at pet stores are often kept in acclimatization bags until this process is complete.
