4.2: Strategies for dealing with a changing environment

There are lots of amazing and sometimes bizarre adaptations out there in the world. For example, some species of frogs (e.g., wood frogs) that live in temperate climates can tolerate the freezing of their blood and other tissues. These frogs allow about 65% of their bodies to freeze solid, stop breathing, and stop their heart when temperatures drop below freezing. Come spring, as temperatures rise, the frog’s body thaws and basic motor functions restart, allowing these frogs to survive incredibly harsh winter conditions. Other examples of interesting adaptations include carnivorous plants that obtain their nutrients from insects (e.g., pitcher plants), or rodents (kangaroo rat) that obtain enough water from metabolism that they do not need to drink water at all.

Figure \(\PageIndex{1}\): Frog (photo by Patti Black on Unsplash), pitcher plant (photo by Adrian Pingstone released to the public domain), and kangaroo rat (US Fish & Wildlife).

While each of these examples are fascinating in their own right, perhaps a better place to start when thinking about adaptation are the basic, or broad strategies that organisms have adapted to survive in the environment. Specifically, if we think about the fact that the environment that an organism lives in can vary considerably. The environment can vary temporally, on both short and long-term time scales, and spatially in terms of both abiotic and biotic factors. For example, the environment an organism experiences can change in temperature, precipitation, amount of sunlight, water availability, oxygen concentration, salinity, atmospheric pressure, etc. This can create problems for living things because most cellular functions (think enzymes, or neurotransmitters) require specific conditions for proper function. Biotic components of the environment can also change with time or space, including things like the availability of prey, the abundance of predators or competitors, or access to potential mates. While different groups of plants and animals may have solved different components of dealing with this variability in different ways, more broadly we can think of two basic solutions or strategies for dealing with environmental variation: conform or regulate.

Conforming is when an organism allows their internal environment to fluctuate with the external environment; we might call an organism that conforms a “conformer” for that particular environmental variable. An example of a conformer to external temperature is a frog that allows its body temperature to fluctuate with the environment (Figure \(\PageIndex{2}\)A). As the external temperature increases or decreases, the internal temperature of the frog increases or decreases along with the external environment.

If we’re thinking just about temperature, we often describe organisms using conforming strategies using the terms ectotherm (an animal that relies on the external environment to regulate its internal body temperature), or poikilotherm (an animal that varies its internal body temperature within a wide range of temperatures).

Figure \(\PageIndex{2}\): Basic strategies for dealing with fluctuations in the environment: conform or regulate.

Regulating is when an organism attempts to regulate or maintain a constant internal environment despite any environmental fluctuations; we might call an organism that regulates a “regulator” for that particular environmental variable. An example of a regulator for external temperature is a dog that attempts to maintain its internal body temperature within a relatively narrow range despite fluctuations in the external environment (Figure \(\PageIndex{2}\)B). As the external temperature increases or decreases, the internal temperature of the dog remains nearly the same with some limitations at extreme temperatures.

If we’re thinking just about temperature, we often describe organisms using regulating strategies using the terms endotherm (an animal that regulates its own internal body temperature through metabolic processes), or homeotherm (maintains a constant internal body temperature, usually within a narrow range of temperatures).

Some organisms can differ in their strategy for different regulatory processes. For example, salmon are thermoconformers, but osmoregulators when they move between marine (saline) and freshwater environments..

There are costs and benefits to each of these basic strategies. For example, conformers will invest less energy into maintaining their internal environment, but can experience compromised cellular functions. On the other hand, regulators can live in a wider range of environments without experiencing reduced cellular functions, but they expend a great deal of energy to maintain their internal environment (Figure \(\PageIndex{3}\)).

Figure \(\PageIndex{3}\): Theoretical costs and benefits of an organism regulating their internal environment or conforming to the external environment.

In addition to being a conformer or regulator, organisms may also be avoiders that will escape changes in the environment by moving locally or migrating long distances (read more about this in the behavioral ecology chapter). Other types of the “avoiding” strategy could include organisms that undergo some type of dormancy, which is when an organism decreases their metabolic activity under extended unfavorable conditions in order to conserve energy.

Examples of dormancy in animals include hibernation, a mechanism used by many mammals to reduce energy expenditure and survive food shortages over the winter. During hibernation, the animal undergoes many physiological changes, including decreased heart rate (by as much as 95%) and decreased body temperature. Another type of dormancy in animals, most commonly seen in insects, is diapause, when the organism completely suspends development between autumn and spring.

In plants, dormancy is a period of arrested growth, and is a survival strategy exhibited by many plant species that allows them to survive in climates where part of the year is unsuitable for growth, such as winter or dry seasons. A classic example of dormancy in plants is seed dormancy, where seeds are prevented from germinating during unsuitable ecological conditions. Many plant species that exhibit dormancy have a biological clock that tells them when to slow activity and to prepare soft tissues for a period of freezing temperatures or water shortage. On the other hand, dormancy can be triggered after a normal growing season by decreasing temperatures, shortened day length, and/or a reduction in rainfall.

Many bacteria can survive adverse conditions such as temperature, desiccation, and antibiotics by forming endospores, cysts, or states of reduced metabolic activity lacking specialized cellular structures.

For organisms that regulate components of their internal environment to big changes in the external environment, one key question we might have is: how do they do this? Mechanistically, the process of adjusting the internal environment in response to an external change is described as acclimation.

Acclimation

Acclimation is the process in which an individual organism adjusts to a change in its environment (such as a change in altitude, temperature, humidity, photoperiod, or pH), allowing it to maintain fitness across a range of environmental conditions. Acclimation occurs in a short period of time (hours to weeks), and within the organism's lifetime (compared to adaptation, which is evolution, taking place over many generations). This may be a discrete occurrence (for example, when mountaineers acclimate to high altitude over hours or days) 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.^[1] 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.

Methods of acclimation

Biochemical

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.^[8] In response to certain stressors, some organisms express so-called heat shock proteins that act as molecular chaperones and reduce denaturation by guiding the folding and refolding of proteins. 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.

Morphological

Organisms are able to change several characteristics relating to their morphology in order to maintain performance in novel environments. For example, birds often increase their organ size to increase their metabolism. This can take the form of an increase in the mass of nutritional organs or heat-producing organs, like the pectorals (with the latter being more consistent across species^[9]).^[10]

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.^[13]

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 acclimation bags until this process is complete.^[15] Lowe & Vance (1995) were able to show that lizards acclimated to warm temperatures could maintain a higher running speed at warmer temperatures than lizards that were not acclimated to warm conditions.^[16] Fruit flies that develop at relatively cooler or warmer temperatures have increased cold or heat tolerance as adults, respectively.^[17]

Humans

The salt content of sweat and urine decreases as people acclimatize to hot conditions.^[18] Plasma volume, heart rate, and capillary activation are also affected.^[19]

Acclimation to high altitude continues for months or even years after initial ascent, and ultimately enables humans to survive in an environment that, without acclimation, would kill them. Humans who migrate permanently to a higher altitude naturally acclimatize to their new environment by developing an increase in the number of red blood cells to increase the oxygen carrying capacity of the blood, in order to compensate for lower levels of oxygen intake.^[20][21]

Sources

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2. Oxford Dictionaries, Oxford Dictionaries Online, Oxford University Press.
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Contributors and Attributions

Written by Dan Wetzel, and modified by Dan Wetzel from the following sources:

• Acclimation section from Wikipedia: https://en.wikipedia.org/wiki/Acclimatization
• Information on plant dormancy from: https://en.Wikipedia.org/wiki/Dormancy