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Population Ecology Theory

Kelly Carroll, Elizabeth Friedl, Christianlly Cena
  • Author
    Kelly Carroll

    Kelly earned a PhD in Microbiology and immunology from the University of Louisville. She has experience doing scientific research as well as teaching university biology and chemistry. She is a freelance writer and runs the early education blog Hey Kelly Marie, a passion project.

  • Instructor
    Elizabeth Friedl

    Elizabeth, a Licensed Massage Therapist, has a Master's in Zoology from North Carolina State, one in GIS from Florida State University, and a Bachelor's in Biology from Eastern Michigan University. She has taught college level Physical Science and Biology.

  • Expert Contributor
    Christianlly Cena

    Christianlly has taught college Physics, Natural science, Earth science, and facilitated laboratory courses. He has a master's degree in Physics and is currently pursuing his doctorate degree.

Learn what population ecology is and its definition. Discover the characteristics of population ecosystems and see population ecology examples. Updated: 05/23/2022

Table of Contents


What Is Population Ecology?

Population ecology is the study of population change over time. A population is the number of a species present in a location at a designated time. The population ecology definition includes the explanations and reasons behind population changes. An introduction to population ecology includes the patterns of population size and fluctuations, as well as geographical distribution. Population ecology studies investigate population growth and spread, how populations interact with the environment, and how members of a population interact with one another. The patterns of populations can be affected by instances of dramatic outbreaks, regional extinction, and periodic cycles of abundance, as examples.

A metapopulation is an assembly of populations. Metapopulation is sometimes described as a "population of populations." The study of a metapopulation of a location includes the population's organisms and species that exist there over time. This study is in opposition to the approach of studying just one species at a time.

The field of population ecology is important in the management and conservation of species. For example, studies can approximate the lowest population size that a species is viable. Below that population size, the species is vulnerable to accelerated extinction.

Population Ecology Examples

One real-world example of population ecology is the study of infectious disease patterns in the human population. By understanding the level and distribution of disease, as well as the implications of the disease on health, population ecology can spur the creation of vaccines. Additionally, population ecology studies can determine where the vaccines should be administered.

Another population ecology example is the study of forests and the harvesting of trees. Population models can drive decisions as to what are reasonable harvesting rates and strategies. When used effectively, population ecology studies can help find an effective yield. Additionally, determining the minimum viable population can help keep a species of tree or a forest from being eliminated.

A third example is the study of amphibian species. It is estimated that over a quarter of amphibian species are under threat of extinction. Population ecology can measure the fluctuations of a population size and determine if it is growing, shrinking, or staying the same. Additionally, population ecology studies can help understand why this is the case. Population models can predict and quantify the likelihood of species survival and breeding.

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  • 0:00 What is Population Ecology?
  • 0:45 Population Factors
  • 1:31 Population Growth
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Characteristics of Population

An ecosystem is the assembly of various species living in a community within an environment. Studies of population ecosystems include the ways the species within an ecosystem grow, change, and interact and the reasons why this is so. Species can interact through preying on one another, competition over resources, and disease spread, among other factors. The defining characteristics of a population include the distribution, abundance, density, age structure, and sex structure.


The distribution of a population describes the dispersion of a population in a specific location. The distribution is where the species lives and can be determined for the entire planet, a nation, a continent, or a smaller geographic locale. Population distributions can be described as equally-spaced or uniform, randomly distributed, or in a clustered manner called clumped dispersion. An example is the distribution of the human species. The southern hemisphere, for instance, has a low distribution of humans with less than one tenth of the total human population.

Population distribution is important because it indicates how a population has organized within a location at a designated time. It can also give insight into how a population has spread based on factors like age, sex, and race.


The abundance of a population describes the relative presence of a species within an ecosystem. Abundance indicates the overall sum number of a population. Abundance can be difficult to measure, particularly if the species is difficult to detect or observe and moves quickly.

An estimate of abundance is acquired through sampling a portion of the population that's being studied. This strategy assumes that the sample is indicative of the entire region.


The density of a population is the quantification of population size in relation to a unit of area. It is calculated by dividing the population number by the size of the land mass. A population's density can be affected by natural or man-made factors. Observing and monitoring density can give insight into factors that affect populations, like threats. Density of animal populations can inform the construction of protected land areas and formation of corridor areas.

Age Structure

Age structure describes the relative numbers of individuals in a population in different age divisions. Age structure can be determined for a specific population at a specific point in time. Age structure is affected by the levels of births, deaths, and migration of a population. For example, in a population with high birth rates, the age structure may include more people in younger age groups.

Age structure influences many aspects of a population and its resources. For instance, age structure can determine how many schools are needed or how many potential workers are available to work. Additionally, age structure can help plan to meet the future needs of a population.

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  • Activities
  • FAQs

Population Ecology Word Scramble Activity

For this activity, study the scrambled letters and try to unscramble or rearrange the letters to form a word or phrase that fits the given clues. To do this, you must right-click and print this page. With a pencil and an eraser, neatly write your answers in the blank space provided.

Scrambled Words

_________________________1. ONAOPIPULT

_________________________2. SOLTSCIEGO

_________________________3. NIOREMIATG

_________________________4. EHTESRL

_________________________5. ECIPESS

_________________________6. LIPONTANEXE

_________________________7. NPLAUTIPOO SDEYTNI

_________________________8. XSE AORIT

_________________________9. INTPLAMUPOTOEA

_________________________10. CEEMOYSST


  1. It is a group of interbreeding individuals of the same species, which is isolated from other groups.
  2. They survey ecosystems and assess the diversity and behavior of the different organisms within them.
  3. Refers to the movement of individuals out of the population, for the purpose of permanent relocation of residence, overcrowding, etc.
  4. Example of available resources in the environment that are taken into account by the logistic growth model.
  5. A group of organisms that share similar characteristics and have adapted to a particular set of resources.
  6. Perhaps the simplest and least realistic growth model to describe a change in population density per unit time.
  7. Denotes the average number of individuals in a population per unit of area or space.
  8. The proportion of males to females in the population and indicates the importance of sexual reproduction, the mating system, and capacity for reproduction.
  9. This is defined as a group of interacting populations of the same species.
  10. A system formed by an ecological community and its environment that functions as a unit.



What is a population ecology example?

One example of population ecology is the study of apes in the wild. Studies of their birth, death, distribution, density, abundance, and age structure can give a lot of insight into their wellbeing and the best ways to allocate resources for their benefit.

What is the meaning of population ecology?

Population ecology pertains to the study of groups of people or populations over time. Population ecology also studies the investigation of the reasons why populations change over time.

What are three characteristics of population ecology?

There are several characteristics of populations that are part of population ecology investigations. These characteristics are distribution, abundance, density, age structure, and sex ratio.

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