Population

Population
n., plural: populations
[populaˈt͡si̯oːn]
Definition: an interbreeding group of organisms living together at the same place and time

Living organisms typically prefer to live, grow, and survive in groups. Except for some species that prefer solitude – both distances away from organisms of their own species and from organisms of other species, most of the organisms on Earth prefer interlinked and interdependent lives.

Organisms of a species living together in a group at a particular place are called a “population” in Biology. A population refers to an assortment of organisms in a given location. These organisms, since they belong to the same species, can interbreed and produce more of their kinds. Hence, when asked what is a population in Biology, one can elaborate it like this:

A population is a group of organisms of one species that interbreed and live in the same place at the same time.

But one must be inquisitive of the following ideas:

• “Do all living organisms live in groups?”
• “Why do living organisms live in groups?”
• “How does the population system affect species survival and its continuity?”
• “Is the concept of population exclusive to the field of Biology?”

To know more about these questions and queries, read our article here.

Population Definition

The concept of population is not exclusive to the field of Biology. We can find the ubiquitous use of the term “population” every now and then. Let’s try to understand and define the word “population” as per its usage. Let’s understand what population means in different fields of study.

Population Definition in Science

Population is a “group” in science. It is generally used in the context of Biological Science where it signifies the group of individuals of the same species. It is also used in Statistical Science, such as when referring to the world population.

Population Definition in Biology

A group of organisms of one species that interbreed and live in the same place at the same time (e.g., human population, the population of apple trees, total population of deer in a forest). It is a subset of the total individuals of a species that occupy a certain geographic area in the world. A species can be randomly or systematically distributed throughout the different parts of the world, countries, cities, forests, ecosystems, etc. But a defined set living in a “very” specific geographic dimension is called a population.

Population Definition in Statistics

A population is a set of data from which a statistical sample can be drawn. The data can pertain to business, research, biological study, analytical work, etc. Thus, any grouping of individuals based on some significant characteristic “common feature” for the matter of statistical analysis comprises a population. It is from this population that a sample is drawn. The sample thereby serves as a representative of the population with all the major characteristic features.

Population Definition in Taxonomy

In taxonomy, the population is a low-level taxonomic unit or rank. Starting from the kingdom, phylum/ division, class, order, family, genus, species, there are many taxonomic ranks in a hierarchy that help classify biological diversity and its studies. Below species, there are some informal taxonomic ranks like subspecies, varieties, cultivars, and populations.

Population Definition in Ecology

In Ecology, the meaning of population is similar to as defined in Biology. It is a dynamic entity that comprises individuals that belong to the same species and can reproduce with each other for the continuation of species.

Population ecology is a very interesting subject to ecologists as it helps them understand the role of various ecological factors on population traits like preferences, population numbers, migrations, etc. The size of populations fluctuates with several environmental factors like air, water, sunlight, resource conditions, competition and food availability, disaster probability, frequency, etc. In order to understand and describe populations, the key characteristics to look at are their size and density.

• Size- Example 1: A population with a greater number of individuals has more chances of survival over time and when unprecedented times arrive at their doors because the genetic variability in the bigger population will certainly be more than that in the smaller populations.
• Density- Example 2: A population with low density will have individuals spread over a larger area but with a lesser number of individuals per unit area. Such a spread of population usually makes the chances of mate encounter bleak and rare. Thus, this deprives the individuals in this population of successful reproduction chances.

Population Definition in General

In general, we define a population as a group of people inhabiting a territory. Example-American population, Indian population, Chinese population, the general population of a city, etc.

Population and Biology

The use of the term population is ubiquitous but let’s try to shed some light on the terms usually associated with population in Biology.

Population Biology

The term was coined and first used by Edward Osborne Wilson in 1971 when studying population dynamics in light of mathematical and analytical models. Population biology is an interdisciplinary field that deals with concepts of Ecology, Statistics, Genetics, and Mathematics altogether. Population biology refers to the biological study primarily concerned with the growth and regulation of population size, population genetics, demography, life history evolution, and the interactions among species.

Population ecology deals with the various ecological factors that affect the populations and their characteristics like abundance, distribution, and composition. It’s a subset of ecology that takes into account the birth rates and death rates in populations. It also takes into account the immigration and emigration rates in a population. It is actually the dynamics of the population of species. It attempts to explain the ways by which species populations interact with their environment.

• Population Size

The total number of representative individuals in a given population at a given time is called the population size. Population size is affected by the intrinsic rate of increase (also called the per capita growth rate) of the population. The carrying capacity of the population is the maximum population size that a given environment can sustain. If the population size increases beyond the carrying capacity, the availability of resources becomes limited and sustainability comes at a fall-off limit.

• Population Bottleneck

Population bottleneck is that breakout threshold limit at which either a population recovers its original numbers or dies to extinction after a man-made or natural disaster hits it. It is characterized by a sudden and sharp reduction in the population size. There could be several reasons for this sharp reduction like environmental and natural calamities like cyclones, forest fires, hailstorms, floods, droughts, disease outbreaks, etc, or manmade disasters like the extinction of a species that this population depended on for its food resources, life cycle completion, etc, intentional killing of species, overexploitation for human needs, etc. It generally occurs for a short period of time.

• Population Genetics

Population genetics deals with the various variations at the allelic level among the individuals of a population. It also takes into account how these allelic variants pass on from one generation to another, and how parents pass the variations in each gene (allelic variations) to their progeny. Population genetics is an interesting subject because it helps you track the changes in the population composition over time (temporal changes in population) alongside knowing the varied roles different evolutionary forces play in this changing procedure.

• Population Decline

Population decline refers to a decline in the population of any organism.

• Overpopulation

Overpopulation is an increase in the population of any species exceeding the carrying capacity of an ecological niche.

Population Examples

There are various examples of population:

1. Populations under threat of extinction:

• Northern elephant seals’ populations – Due to the overhunting of these organisms in the 19th century, their populations declined and neared extinction. Even with the efforts to curb this and correct human mishandling over the years, some things couldn’t be turned back to the past. A similar thing happened with northern elephant seals and they lost their genetic variability. The current genetic variation in their population is very low.

• Cheetah populations – Cheetah populations are under threat of extinction because of the low genetic variations like elephant seals. It’s the planet’s fastest land animal and losing such a precious species and its population is a big loss for the planet.

2. Populations of bacteria:

Various different bacteria live in our guts. The roles they perform in the proper functioning of the body are indispensable. The current trend of probiotics and prebiotics in the superstores has a lot to do with the populations of microbiota in our gut. Regular intake of fermented food, pickles, curd, probiotic food, and drinks has always been a part of the traditional lifestyles of old people across the world. All these food types help in maintaining a healthy population of beneficial bacterial populations in our gut.

Try to answer the quiz below to check what you have learned so far about populations.

Time's up

Further Reading

• Population Growth and Survivorship – Biology Online Tutorial
• Population Regulation in an Ecosystem – Biology Online Tutorial
• The Gene Pool and Population Genetics – Biology Online

References

• Hartl, Daniel (2007). Principles of Population Genetics. Sinauer Associates. p. 95. ISBN 978-0-87893-308-2.
• Hoelzel, A. R., Halley, J., O’Brien, S. J., Campagna, C., Arnbom, T., Le Boeuf, B., Ralls, K., & Dover, G. A. (1993). Elephant seal genetic variation and the use of simulation models to investigate historical population bottlenecks. The Journal of heredity, 84(6), 443–449. https://doi.org/10.1093/oxfordjournals.jhered.a111370
• Marczewski, T., Ma, Y. P., Zhang, X. M., Sun, W. B., & Marczewski, A. J. (2016). Why is population information crucial for taxonomy? A case study involving a hybrid swarm and related varieties. AoB PLANTS, 8, plw070. https://doi.org/10.1093/aobpla/plw070

©BiologyOnline.com. Content provided and moderated by Biology Online Editors.