Biological exponential growth
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Biological exponential growth is the unrestricted growth of a population of organisms, occurring when resources in its habitat are unlimited. Most commonly apparent in species that reproduce quickly and asexually, like bacteria, exponential growth is intuitive from the fact that each organism can divide and produce two copies of itself. Each descendent bacterium can itself divide, again doubling the population size. The bacterium Escherichia coli, under optimal conditions, may divide as often as twice per hour. Left unrestricted, a colony would cover the Earth's surface in less than a day.[1][2]
Resource availability is essential for the unimpeded growth of a population. Ideally, when resources in the habitat are unlimited, each species has the ability to realise fully its innate potential to grow in number, as Charles Darwin observed while developing his theory of natural selection. In almost all situations (with exceptions, such as a laboratory) this is unrealistic; there is simply a finite quantity of everything necessary for life. As the population approaches its carrying capacity, the rate of growth decreases, and the population trend will become logistic.[3]
If, in a hypothetical population of size N, the birth rates (per capita) are represented as b and death rates (per capita) as d, then the increase or decrease in N during a time period t will be
(b-d) is called the 'intrinsic rate of natural increase' and is a very important parameter chosen for assessing the impacts of any biotic or abiotic factor on population growth.[4]
Any species growing exponentially under unlimited resource conditions can reach enormous population densities in a short time. Darwin showed how even a slow growing animal like the elephant could reach an enormous population if there were unlimited resources for its growth in its habitat.
See also
References
- ^ "Exponential & Logistic Growth". Khan Academy. Retrieved 15 January 2022.
- ^ Marr, A G (June 1991). "Growth rate of Escherichia coli". Microbiological Reviews. 55 (2): 316–333. doi:10.1128/mr.55.2.316-333.1991. PMID 1886524. Retrieved 15 January 2022.
- ^ Rye, Connie; Wise, Robert; Jurukovski, Vladimir; DeSaix, Jean; Choi, Jung; Avissar, Yael (October 21, 2016). Biology. Houston, Texas: OpenStax. Retrieved 15 January 2022.
- ^ Rye, Connie; Wise, Robert; Jurukovski, Vladimir; DeSaix, Jean; Choi, Jung; Avissar, Yael (October 21, 2016). Biology. Houston, Texas: OpenStax. Retrieved 15 January 2022.
Sources
John A. Miller and Stephen B. Harley zoology 4th edition
External links
- "An Introduction to Population Growth". Sunny B. Snider (College of Agriculture, California State University, Chico) & Jacob N. Brimlow (College of Agriculture, California State University, Chico). Nature Education Library, 2013.