General Ecology 2019 – Lab 5 Human Population Growth

General Ecology 2019 – Lab 5 Human Population Growth

THE DEMOGRAPHIC TRANSITION Step 1 Introduction The “Demographic Transition” refers to the transition from high birth and death rates to low birth and death rates as a country develops from a pre-industrial to an industrialized economic system. The concept is based on an interpretation of demographic history that was developed by the late 1920s by Warren Thompson. Today we recognize that shifts towards lower birth rates (lower fecundity) are critical for reducing human population growth rates, the resources we use, and our ecological impact. At the most basic level, the increase or decrease in population can be calculated by following the simple formula: Birth Rate – Death Rate + Immigration = Growth Rate. The simulator that we will use today does not take immigration into account, but does allow us to explore in detail the influence of birth and death rates on human population growth. The birth or death rate is the total number of births or deaths per year. However, as you’ll see in the simulator, birth rates are normally expressed as number of births per woman (over her whole life) and death rates as a percentage of people who die in each age group. Simulations and Data In a web-browser, open the following URL to launch the population simulator: http://www.learner.org/courses/envsci/interactives/demographics/demog.html To get a sense of this continuum of birth and death rates across countries, start by running the simulator to 2050 for all 9 countries (using all other default values). Select the country in the top-middle and click on RUN button to run the simulation through to 2050. Click RESET between simulations. Using the data table below, record the final birth and death rates, and the population growth rates at the end of the simulation. Rank the countries by final population growth rate from highest (earliest in the demographic transition) to lowest (farthest along the transition). Questions NOTE: Your answers throughout this lab should be well written short-paragraph answers, not individual words or bullets. This is a lab that should prompt a good amount of thinking, and that should be represented in your answers. 1. Identify the country that is earliest in the demographic transition, and the one furthest along in the demographic transition. 2. How do you think living conditions differ between the country furthest along in the demographic transition compared to the country earliest in the transition? Consider a number of factors, like housing, healthcare, and family structure. 3. How would living conditions in these two countries affect both birth and death rates? 4. Think of three social/cultural factors that contribute to lower birth rates in the countries further along in the demographic transition. How might these social conditions be encouraged to emerge in less developed countries? Step 2 Introduction The overall population growth rate is only one of the differences among countries in different stages of the demographic transition. The age-based population structure is also greatly affected. Note that the average fertility rate for women in the United States is 1.98, which is a “replacement rate”. This means enough children are born to replace their parents. The death rate likewise remains a relatively constant 1 of 5 percentage for each age group. Simulations and Data For each of the countries, look at the starting population pyramid (2015). Record in the data table how you predict the pyramid shape will change before you run the simulator through to 2100. After clicking RUN and waiting for the simulation to get to 2050, click RUN again to simulate through to 2100. Record in the data table the actual simulated shape of the pyramid. Questions 5. 6. 7. How does the shape of the 2100 population pyramid differ from most developed to least developed country? (most- United States, least- Nigeria) Run a population simulation of the USA, with a birth rate of 1 per woman and death rate of 2%. How might this impact the quality of life in the U.S.? Think about the sizes of the older and younger populations relative to the working population, and how this might relate to resource needs versus resource supply from the working population. Countries that are now “late” in the demographic transition generally began it earlier than other countries, or, as with China, pursued the transition more aggressively through social policies that limit the number of children per family (introduced between 1978 and 1980 and began to be formally phased out in 2015). The USA is fairly late in the transition. What do you suppose its demographic pattern was like 100 years ago? What about China 100 years ago? Based on what you know of these and other countries, explain what factors might prompt women to have fewer children and to have children later in life. POPULATION MOMENTUM Step 1 Introduction In this section of the lab, we explore population momentum, defined as the time lag between a change in birth/death rates and the slowing of population growth. In lectures, we are looking at the underlying process of how time delays shape population dynamics. Here we will explore the kinds of patterns that can be generated, many of which are not intuitive. We will first explore the effects of changing the age of reproduction on population growth, using Nigeria as an example. The questions will ask you to consider the human and ecological impacts of unchecked population growth, as well as the human cost of China’s successful attempt to curb its own growth via a family-planning law that restricted each family to one child. Simulations and Data Select Nigeria from the COUNTRY pull down menu in the top right, run the simulator with the default settings to 2050, and record the results in your Data Table. Predict what will happen when the average age of childbearing women is increased by 5 years (fewer teenage pregnancies) and record your prediction. Note that this doesn’t change the number of children born to each woman; it changes the age at which most births occur in the women’s lifespan. Run the simulator, increasing the childbearing age by 5 (youngest child-bearing age is 20) and 15 years (youngest child-bearing age is 30) and record your results. To make these adjustments, under Vital Rates click on the edit “pencil” icon on the button for Birth. Once the edit window opens, use the horizontal arrows to the right to adjust the earliest child bearing age. Be sure to click “Apply” to save the changes and don’t forget to RESET the simulator between runs! What would happen if Nigeria suddenly had the same birth and death rates as the USA? Using the same Birth edit window, choose “USA” from “Use rates from” pull-down menu, then click “Apply”. Open the edit widow for Death, and also switch the death rates to “USA”, then click “Apply”. Run the simulator for 150 years (3 consecutive runs of the simulator). While doing so, watch the shape of the population structure (the graph by age group). Describe the shape of the pyramid at the end of 150 years. Questions 8. 9. Explain how and why the Nigeria pyramid shape is changed so substantially by switching to USA birth and death rates. Explain how an increase in the average childbearing age group change the population. 2 of 5 10. Why do you think that more developed countries, later in the demographic transition, tend to have older childbearing women than less developed countries? Step 2 Introduction Now let’s look at Italy, a country with a population structure almost the opposite to that of Nigeria. Make a prediction about how this difference in population structure might affect the growth of the population, given what you know about the ages at which people are able to bear children and the ages at which people are likely to die. Simulations and Data Apply the process explained in Step 1 to Italy. Select Italy from the COUNTRY pull down menu, run the simulator with the default settings to 2050, and record the results in your Data Table. Predict what will happen when the average age of childbearing women is increased by 5 years (fewer teenage pregnancies) and record your prediction. Run the simulator, increasing the childbearing age by 5 and 15 years and record your results. Return to the simulator and change the birth and death rates to those of the USA. Again, run the simulator for 150 years, observing what happens to Italy’s population pyramid. Questions 11. Did the pattern of population change match your prediction? If not, why not? 12. Compare the final population pyramid for Italy to the one you described for Nigeria. How do they compare, and why are they similar or different? 13. How are Italy’s numbers different from Nigeria’s? What do you think accounts for the difference? 14. Many Western European countries are giving monetary incentives to employees who have multiple children. Why would they do this? How would a baby boom change Italy’s demographics? 3 of 5 DATA TABLES The Demographic Transition: Step 1 Final Final Death Population Growth rate Country Birthrate Rate (%) 2015 Brazil Population Growth rate (%) 2050 Relative place in Transition in 2050 China India Indonesia Iraq Italy Japan Nigeria USA The Demographic Transition: Step 2 Country Predicted 2100 Pyramid Shape Simulated 2100 Pyramid Shape Brazil China India Indonesia Iraq Italy Japan Nigeria USA Population Momentum: Step 1 Nigeria Default +5 Prediction + 5 years Sim. +15 years Sim. Birth rate Death rate Population growth Shape of Nigeria pyramid using USA birth and death rates (draw digitally, or draw on paper and paste in a picture): Population Momentum: Step 2 Italy Default +5 Prediction 4 of 5 + 5 years Sim. +15 years Sim. Birth rate Death rate Population growth 5 of 5

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