A population pyramid is a graphical illustration that shows the distribution of various age groups in a population (typically that of a country or region of the world), which forms the shape of a pyramid when the population is growing. It is also a tool used in ecology to determine the overall age distribution of a population; an indication of the reproductive capabilities. The graph typically consists of two back-to-back bar graphs, with the population plotted on the X-axis and age on the Y- axis, Males are conventionally shown on the left and females on the right in five-year age groups (also called cohorts). They may be measured by raw number or as a percentage of the total population.

The shape of a country’s population pyramid tells a story about the history of its population growth. For example, a high- growth-rate country has a pyramid that is narrow at the top and wide at the bottom, showing that every year more children have been born than the year before. As family size decreases and women in a society have fewer children, the shape of the pyramid changes. A population pyramid for a post-industrialized country that has negative growth would be narrower at the bottom than in the middle, indicating that there are fewer children than middle- aged people.

A more rectangular population pyramid indicates a population which is neither growing nor declining. There are similar proportions in each age group, apart from at the oldest ages (due to mortality). A top-heavy population pyramid with higher proportions in older age groups indicates a declining population. This may result from a long period of below replacement fertility, alongside low death rates.

This oddly shaped pyramid below for Grant County, North Dakota, suggests a population decrease, that might be due to any number of factors, including: high death rates within certain age groups low birth rates increased emigration from the area.

…in developing industrialized countries… EARLY. Each successive age group is smaller than the preceding age group. The working age population (shown in orange) has to provide for a comparatively large population of children. However, children can help their parents in growing food, collecting firewood, etc. Middle:. The age pyramid is dominated by the working age groups. The working age population is potentially well able to support the old and the young. Notice the left-right asymmetry. This is because women tend to live longer than men. LATE. Now the pyramid is almost rectangular in shape. The working age population needs to support a large population of older people EXPANDINGSTATIONARY CONTRACTING

This age distribution analysis graph shows negative growth. These projections are for Japan, in the year Talk with your neighbor about whether this graph shows positive population growth, “0” population growth, or negative population growth. Should human goals include negative growth, or replacement level fertility?

What trends might a top-heavy population pyramid indicate? What trends might a bottom-heavy population pyramid indicate? What trends might a rectangular-shaped population pyramid indicate? Describe the demographic transition in the population pyramid above. At what stage might this population be, and how do you know?

Right now, the world’s population is growing at an average rate of 1.4% per year, giving it a doubling time of approximately 50 years. The rapid addition of more people has significant implications. The Earth, after all, is a finite system, and cannot sustain continued exponential growth indefinitely. The absolute maximum population the Earth can sustain at a reasonable average living standard for its inhabitants is called the carrying capacity. Every habitat, no matter how rich, contains limited supplies of important resources like food, shelter, mineral nutrients, water, and light. When a population grows rapidly, it consumes these resources at an increasing rate. The resources that limit the growth of a certain population are known as limiting resources, or factors.

70 / % growth = doubling time 70 / doubling time = % growth There's an easy way to calculate how quickly something (a population, or even a monetary investment) will double when it's growing exponentially. Just divide 70 by the percent increase, and you've got the doubling time. For example, if you hear that the population of your town is growing by 2% per year, that means it will double in just 35 years! (70/2=35) If you hear your that your town’s population is due to double in 35 years, you can calculate it’s growth rate. (70/35=2%). Rate is always shown as a percent!

Looking at the time line below, we know it to0k 45 years for Earth’s population to double. (from 2 billion to 4 billion). Based on the rule of 7o, predict how long before we get to 8 billion. 70/45 =1.6% growth rate 70/1.6% = 45 years. Then, simply add 45 years to 1975, and you get the expected year for 8 billion humans…or I think we’ll be shy of that! 7.scuhn054Q5WXvFD9uRG9Xw.0&utm_referrer=http%3A%2F%2Fwww.google.com%2Furl%3Fsa%3Dt%26rct%3Dj%26q%3D%26esrc%3Ds%26source%3Dweb%26cd%3D2%26ved%3D0C C4QFjAB%26url%3Dhttp%253A%252F%252Fwww.worldometers.info%252Fworld-population%252F%26ei%3DEKdfU52sDfSr2AXBoYD4AQ%26usg%3DAFQjCNErbPyUCHWnx- PRFhnobEtJRV06Mg

A city has a growth rate of 5%. How many years will it take to double its population? If the growth rate were 7%, how many years will it take to double? Your town is due to double in population in 20 years. What is the growth rate? 70/5 = 14 years 70/7 = 10 years 70/20 = 3.5%

Human growth patterns exhibit exponential qualities. This means that in a given time, the population will double. Humans exhibit the same type of growth patterns as bacterial infections! What are some of the limiting factors for these bacterial colonies? The petri dish was half full at 11:59am. When will the bacteria run out of space? Before you answer this question, consider the fact that at 11:55 am the petri dish was only about 3% full. Would you likely recognize a space problem in the next 5 minutes? Space Food Oxygen, if they’re aerobic

On a graph, an exponential curve is often perceived as a “J”. An “S” shaped curve demonstrates “logistic” growth. This section represents the area of exponential growth. The population of rabbits doubles frequently. This area represents the carrying capacity (K) of this particular ecosystem. This is the point where there is just enough food and other resources for the existing rabbit community. No more can be supported. What do you think happens to the graph when the population exceeds the carrying capacity for any length of time?

The U.S. population is undergoing at least two major shifts: a significant change in its geographic distribution and a similarly important change in ethnic composition. Immigration--accounting for 1/3 of the present annual growth--is also an undeniable factor. Demographers use a numerical equation to express the rate at which all populations grow. Considering the world as a whole, the fundamental demographic equation is: Population Growth Rate = Birth Rate  Death Rate Most demographers modify this equation a bit. In order to take immigration, and emigration into consideration, the following equation is used: Population Growth Rate = Rate of Increase  Rate of Decrease Immigration and emigration both impact populations.

South: 37 % of Total U.S. Population Northeast: 18 % of Total U.S. Population Midwest: 22 % of Total U.S. Population West: 23 % of Total U.S. Population What do you notice about the NE in this map? Area Population April 1, 1990 Average April 1, 2000 Average April 1, 2010 Average United States 248,709, ,421, ,745,538 Region 1 Northeast50,809,229 20% 53,594,378 19% 55,317,240 18% Midwest59,668,632 24% 64,392,776 23% 66,927,001 22% South85,445,930 35% 100,236,820 36% 114,555,744 37% West52,786,082 21% 63,197,932 22% 71,945,553 23%

Take a minute to discuss this graphic with your partners. Is there anything that surprises you? Why do you suppose ethnic groups still tend to “stick” together?

What type of growth is the human population currently exhibiting? Why can exponential growth not be sustained forever? Use your academic vocabulary! Describe how the population growth patterns in the US are currently trending by region. What factor must demographers take into consideration when calculating population growth?