# What is negative population growth?

Feb 25, 2016

A negative population growth rate occurs when the number of people/ species are reduced.

#### Explanation:

To further expound upon this point lets take a quick look at population growth. Population growth is defined as: an increase in the number of individuals in a population (be it birds, fish, humans, or even unicorns!). A rate is a ratio that allows us to compare two objects with different units of measure.

All my senseless rambling aside, a population growth rate is the rate at which a population increases within a given time period. It is expressed mathematically as: the change in population (difference in population) divided by the length of time (difference in time), the expression below should help:

Population growth rate= $\frac{P \left(t 2\right) - P \left(t 1\right)}{P \left(t 1\right) \left(t 2 - t 1\right)}$

P(t2) is equal to the population at the end of the time in question, the most recent time (time closest to today)

P(t1) is equal to the population at the start of the time in question, the time furthest from today

(t2-t1) is the difference in time, (t2) specifically, is the the date furthest from today, while (t1) is the date closest to today

Note: that the P in front of the parentheses indicates population, without the P the (t)'s represent time

As an example lets take a look at the population in my home state of California between 2000 and 2014:

P(t2): 39 million people

P(t1): 34 million people

(t2): 2014

(t1): 2000

Population growth rate= $\frac{P \left(t 2\right) - P \left(t 1\right)}{P \left(t 1\right) \left(t 2 - t 1\right)}$

= $\frac{39 - 34}{\left(34\right) \left(2014 - 2000\right)}$

=(5)/((34)(14)

=$\frac{5}{\left(476\right)}$

=$0.0105$

To get a percent we multiply by 100 and get an annual increase in population of about 1.05%. We can multiply this value by 4 (the number of years) to determine the total percent increase across all 4 years (the population increased in Ca by 4.2% in 4 years).

To answer your question more directly, a negative population growth occurs when the population of a species declines, this could be due to any number of factors including: death rates exceeding birth rates or immigration.

I know this is long and convoluted, thanks for sticking with me!