In class on Friday we began discussing human population. We started by watching this video that illustrated the human population growth since the beginning of recorded history:

We just finished studying population ecology, how populations grow, and how they impact the environment and now we are moving into the human population and how it is growing and effecting the environment. The title written on the board was The Human Population – Our biggest environmental problem. Some people say that human population is at the core of environmental problems. Why? What are human impacts? We started with the human population size and growth.

The current human population is at 6.8 billion. How did the population get there? The human population grows like any other population we have studied and its current growth looks like a J or exponential growth curve.

Global Population Graph


This is a graph of the Global population over time. The human population grew low and slow until the Industrial revolution and modern medicine, when it took off. We dissected the growth in class and when population reached each billion. 1800- 1st billion, 1930- 2nd billion, 1960- 3rd billion, 1975- 4th billion, 1987- 5th billion, 1999- 6th billion, 2010- 6.8 billion. Then we looked at the difference between each billion. The first billion took 1800 years to reach, the second took 130 years, the third took 30 years, the forth took 15 year, the 5th took 12 year, the sixth took 12 year, and we are almost at our 7th. There is a clear increase in the rate at which the human population grows but the amount of years between the billions seem to be becoming more constant which might indicate we are approaching an inflection point. Mr. Willard also told us that the AGR, or annual growth rate (also classed rate of natural increase), during 1960 was 2.1% and the AGR now is 1.2%, so the annual growth rate has decreased by almost half. AGR is related to doubling time, which is the time it takes for a population to double. When doubling time decreased the total population increases (learned the equation for calculating doubling time in class and it will be lower in the post) and right now the doubling time has decreased because the AGR has decreased.

The other part of class was spent learning equations needs for the human population unit. There are 3 basic type of problems for this unit. The first is doubling time by rule of 70. The doubling by rule of 70 equation is:

Rule of 70

In this equation the AGR has to be in percent form and then you divide 70 by that to get the doubling time. This is an example of one of those problems:

Doubling time by rule of 70 equation

So the AGR in this problem is 1.5% and the doubling time is 47 years. If the year was 2007 then, in this example, the population would double by 2054.

The second type of problem we learned was how to calculate annual growth rate. This equation is:

Annual growth rate equation

CBR stands for crude birth rate, which is births + immigration, and CDR stands for crude death rate, which is deaths + emigration. Crude means out of 1,000. The original equation is ((CBR-CDR)/1,000) x 100, but the 2 zeros in the 100 and 1,000 cancel out and so the equation simplifies down to the equation you see above. This is an example of an annual growth rate problem:

Annual Growth Rate Problem

In this equation 14= crude birth rate, 9= crude death rate and the AGR come out as.5%.

The third type of problem we learn was annual increase. This type of problem is to find out how much a population will grow in a year. In this type of problem you are given a # for a population and the AGR(%) at the time. You use these to find how much the population will grow in the next year. In class we used the example that in 2007 there was a population of 300,000,000 and the AGR at the time was.5%. This is how to solve the problem:

We are not allowed to use calculators on the exam so in class instead of using a lot of zeros like in #1, we used scientific notation as illustrated in #3. For this equation The AGR can not be in percent form for this problem the.5% turns into.005 or 5.0 x 10^-3 in scientific notation. You need to multiply the 300,000,000 or 3.0 x 10^8, the population, by the annual growth rate, and when using scientific notation keep in mind when multiplying numbers with exponents you add the exponents. So you get your result (when using scientific notation) by multiplying 3 by 5 and adding the exponents of the 10s, 8 and -3, which gives you 5. 15 x 10^5 (1,500,000 expanded). To get the total population after a year you just add the 1,500,000 to the total population of 300,000,000 and you have what the population will be, which in this case is 301,500,000.

That basically what we discussed and learned in class and the 3 types of problems we need to know. Keep in mind you can’t use calculators on the exam so brush up on your long division and stuff like that.

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