Hapter 18 Ecology of Organisms and Populations


Age Structure and Population Growth


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Age Structure and Population Growth – You can determine a lot by simply looking at the age structure of a population. Knowing the average life expectancy and how many individuals are in each generation (seniors, middle age, and young) gives you some predictive power of what the future holds. Think about it, why do we hear so much about the “Baby Boomers?” Because very soon a lot of people are going be retiring and applying for social security benefits and other entitlement programs.
Look at the diagram below – it shows the age structure of 3 different countries and the projected population growth based merely on age structure. If you were to look at impoverished nations versus industrialized nations you see some more interesting trends. It turns out that the poorest of countries are experiencing the most rapid population growth of all – you may ask why? There are lots of factors that play a part in this.

Accelerated human population growth will cause many things to occur in our own lifetime – increased war, famine, disease, religious mania, environmental degradation.
The Rule of 72 – How long does it take for a population to double? If you take the average % population growth of a population and divide that into the number 72, you will get the number of years it will take for that population to double.
Example: In some poor regions the annual population growth is around 3.5%; that doesn’t sound like much does it? So how many years will it take for that region to double in humans?
72 ÷ 3.5 = 20.5 years. So, in about 21 years the population will double. If we are talking about a poor country where the people are already having a tough time, in 21 years they will be having double the problems. This leads to things like famine and genocide – sound familiar? It should, because these are the scenarios that many regions are facing today (Darfur, Zimbabwe, ect).
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