Environmental variation is inherent in all populations and is the variation which is caused not from genetic factors, but rather environmental influences such as climate. The phenotypic variation which an individual possesses is a result of both their genes and their environment. The basic model for visualizing this variation on a trait is as follows:
Vp = Vg + Ve
Vp = variation in phenotype
Vg = variation in gene
Ve = variation in environment
Environmental variation is influenced by the ability of an organism to undergo phenotypic plasticity. This is a genetically based ability which allows an organism to alter their behaviour, morphology or physiology, through compensatory changes to their pre-existing self. These changes increase an organism’s fitness in their changing environment. Environments change continuously over time and different time scales. For example, over an evolutionary time scale, changes occur within the deep ocean. Thus, organisms need to respond to these environmental changes in order to reproduce and survive.
Furthermore, it is important to understand a few terms which are related to this concept of environmental variation:
- Adaptation: This refers to non-reversible changes which occur over long time scales. For example, native organisms living permanently in high altitudes, such as the plateau pika, have evolved genetic adaptations through time to survive this type of environment. This adaptation is a result of evolution and influences populations.
- Acclimatization: This can occur in one generation and can also be reversible. Increasing the red blood cell counts of mountain climbers so that they can better adapt to the high altitude environment, is an example. This influences individuals and not populations.
Within a population, individuals have different phenotypes and one of the factors influencing this diversity is environmental variation. It is environmental variation which allows for different forms of the same gene to exist in a population since under different environmental conditions one gene is favoured over another.
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