Life History

The concept of Life history describes how an organism’s age, size, growth, reproduction and lifespan affect its life cycle. As a result of evolution, these different characteristics usually suit the type of environment that an organism lives in. Consequently, organisms that inhabit predictable environments have different characteristics to those in unpredictable environments.

In a predictable environment the abiotic factors are consistent and so a population of organisms has more time to grow in numbers, therefore becoming overcrowded leading to high levels of competition. Because of this, individuals use most of their energy for growth as a larger body size has a competitive advantage. These individuals also have a longer life span and therefore fewer offspring are produced, with the offspring that are, being larger to increase their chances of survival and consequently, population size remains relatively stable at the environment’s carrying capacity as shown in Figure 1. These characteristics are known as K characteristics.

In an unpredictable environment, the abiotic factors change randomly causing population size to vary massively over time with periods of rapid growth and death as can also be seen in Figure 1. Organisms focus their energy on reproduction due to the high mortality rate as a result of the unstable conditions and are consequently small in size. These characteristics are known as r characteristics

                                                                Figure 1: Comparisons of the growth rates between r and k selected species


‘Idealised patterns of population growth and fluctuation for r-selected and K-selected species’, December 2018, Graphic, Grand Valley State University. Source:  (accessed on 26/01/19)

Key Terms:

Abiotic factors – The physical factors, such as weather and geology, in an environment.

Carrying capacity – The number of individuals that an environment can support without becoming degraded.

Evolution – The process of how different organisms have developed as a result of environmental pressures selecting individuals better suited to them (see Natural Selection article for more information)

Organism – An individual animal, plant, or single-celled life form.

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