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Alberta Education Diploma - Biology 30: Exam Prep & Study Guide20 chapters | 191 lessons | 18 flashcard sets

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Lesson Transcript

Instructor:
*Lauren Posey*

Lauren has taught intermediate reading in an English Language Institute, and she has her Master's degree in Linguistics.

Population growth rate is an important factor to consider when looking at the past and future of a population. In this lesson, you'll learn how to calculate the growth rate.

Think about the town where you live. How long have you lived there? Do you know how much that town has grown since you've been there? If you determine the overall amount the population has changed in the entire time you've been there, this only tells you the change in population size. However, this doesn't really help you think about annual growth or predict future growth for your town. To do this, you need to know the population growth rate.

The **population growth rate** expresses the change in population size as a factor of time. Typically, both for human and non-human populations, we want to know the average annual growth rate. This gives us more information than stating the exact population growth for the entire time period, and allows us to better predict future years of growth or decline for the population.

The standard formula for calculating growth rate is:

*Gr*= *N* / *t*

Here, *Gr* is the growth rate expressed as a number of individuals. *N* is the total change in population size for the entire time period, also expressed as a number of individuals. *t* is time, usually expressed in number of years. Of course, for really quickly growing populations, it might also be expressed in months or some other unit of time. The formula is calculated the same way regardless of the unit of time used.

In order to calculate the overall growth rate, you first have to figure out *N*. This is done by subtracting the initial population (or P1) from the current population, or the population at the end of the time period you are using (or P2). Therefore:

*N*= P2 - P1

Now, let's take a look at few examples that put this formula into practice.

You are looking into the history of your town, and you'd like to know exactly how much the population has grown since 1980. Town records have kept track of the overall population each year. The current population for 2017 is 300,000 people. Back in 1980, the population was only 150,000 people.

First, you need to determine *N*, the overall change in population size since 1980:

*N*= 300,000 - 150,000

So, the total change in population size since 1980 is 150,000 people.

Next, you need to determine the number of years by subtracting the end year from the start year:

2017 - 1980 = 37

So, *t*=37.

Now you can plug all of this information into the formula:

*Gr*=150,000 / 37

So,

*Gr*= approximately 4,054

Actually, it would be 4,054.054, but since a population can't grow by 0.054 of a person, you have to round to the nearest whole number. This means that the population of your town has grown by an average of approximately 4,054 people every year since 1980.

Now let's examine a penguin population over a 10-year time period. When the research began, the penguin population was at 10,000. Now, after the 10-year study has ended, it is at 9,500.

First, calculate *N*:

*N*= 9,500 - 10,000. *N*= -500

You'll notice that *N* is a negative number. This means the overall population has decreased rather than increased. You already know that *t* = 10, so you can plug your information into the formula.

*Gr* = -500 / 10

*Gr* = -50

When you divide a negative by a positive the result is negative, so the growth rate is negative. This means that the penguin population has decreased by an average of 50 penguins per year since the study began.

It is possible that when you calculate *N*, it will equal zero, and therefore *Gr* would equal zero as well. This means the population is in **equilibrium**, and there is no growth or decline.

The **population growth rate** tells you how much a certain population has changed as an expression of time. Annual growth rate is a common unit to use. To calculate this growth rate, you use the formula:

*Gr* = *N* / *t*

where *Gr* equals the growth rate, *N* equals the change in population over the entire time period as a number of individuals, and *t* equals the time period, usually a number of years. *Gr* is also expressed as a number of individuals. *N* is calculated by subtracting the initial population from the current population.

If *Gr* comes out as a positive integer, then the population is increasing. If it is negative, this means the population is decreasing. There is also the possibility that *Gr* will equal zero. In this case, the population is in **equilibrium**, meaning it is neither increasing nor decreasing.

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Alberta Education Diploma - Biology 30: Exam Prep & Study Guide20 chapters | 191 lessons | 18 flashcard sets

- The Human Population: Factors that Affect Population Size 8:26
- Population Growth: Demographic Transition and Malthusian Theories 9:48
- Determining Change in Population Size: Formula & Examples
- Population Growth Rate: Definition, Formula & Examples 5:04
- Population Density: Definition, Formula & Examples 4:07
- Biotic Potential and Carrying Capacity of a Population 6:50
- Logistic Population Growth: Equation, Definition & Graph 4:46
- Exponential Growth: Definition & Examples 5:08
- Open & Closed Populations: Characteristics & Differences in Growth Patterns
- Factors That Influence a Population Growth Curve
- R-Selected Species: Examples & Definition 5:15
- K-Selected Species: Definition & Examples 7:25
- Graphing Population Growth of R-Selected & K-Selected Species
- Go to Population Change in Biology

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