Population Ecology: Definition, Theory & Model

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  • 0:00 What is Population Ecology?
  • 0:45 Population Factors
  • 1:31 Population Growth
  • 3:09 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

In this lesson, learn how population ecologists study populations and their interactions with their environment. You will learn about the various terms and models they use to describe and understand this complex field of study.

What is Population Ecology?

Ecologists study many different aspects of ecosystems. One aspect that is of particular importance is population ecology. This field of study is concerned with populations and how they interact with their environment.

A population is all of the individuals of the same species within an ecological community. Ecologists are interested in the growth of a population, fluctuations in population size, the spread of the population, and any other interactions with the population or between it and other populations.

Ecologists may also study different groups of populations that are not located in the same area but interact at certain times throughout the year. If this group of populations are the same species and can still interbreed, they are a metapopulation. Individuals within a metapopulation may migrate from one population to the other, which can help stabilize the size of the overall population.

Population Factors

Ecologists describe the organisms of populations in several different ways. The distribution of a population is the total area that population covers. The abundance of a population is the number of individuals within that population. Ecologists may also define the number of individuals within a certain space, which is the density of the population.

Ecologists also identify the age structure or sex ratio of a population. The age structure describes the number of individuals in different age classes, while the sex ratio describes the proportion of males to females in that population.

Population Growth

Within any population, individuals are born and individuals die. If there are more individuals being born than dying, the population grows in size, while if more individuals are dying than being born, the population shrinks. Individuals may also enter or leave a population, which is referred to as immigration and emigration.

To better understand population growth, ecologists have created models to study how birth, death, immigration, and emigration affect population size. The simplest model is called the exponential growth model. It says that the change in population size is exponential, or growing at an increasing rate. This is not a very realistic model because most populations do not continue to grow without slowing down.

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