The Basics of Population

Transcription

1 The Basics of Population About 12,000 years ago, several cultures shifted from hunting and gathering to farming. Humans became the first and only species ever to control our own food supply. Steady population growth was the result of controlling the food supply. In the absence of other limiting factors, any population will expand to the limit of its food supply. This happens so reliably that it is considered a law of ecology. Technology By about 1800, major advances referred to as the Industrial Revolution were occurring. Improvements to agriculture, settlement planning, division of labor, mathematics, literacy and science were all foundations of the industrial revolution. Breakthroughs in medicine, nutrition and sanitation brought down child mortality rates and led to longer life spans. The mechanization of agriculture and improvements in food preservation led to even greater increases in food production and availability. Human numbers began doubling at an unprecedented pace. Rates of Growth Past A graph of human population before the agricultural revolution would likely have suggested a wave, reflecting growth in times of plenty and decline in times of want. Graphs of other species' populations continue to look to this day. The graph of recent human population growth is referred to as a "J curve," because it starts out low and skyrockets straight up. Present World population reached 6.6 billion people in At the present rate of growth nearly 77 million people are added per year. The world adds a New York City every month, a Germany every year and a Europe each decade. The United States, with over 301 million people, is growing by nearly 3 million people each year. At this rate, we are one of the fastest growing industrialized nations in the world. We have the third largest population of all nations, preceded only by China and India. At 5% per year, the U.S. also has the highest teen pregnancy rate of any modern industrialized country. Future With a current annual growth rate of 1.14%, world population is projected to double in just 61 years. Our doubling times will be realized if and only if growth rates remain constant. Doubling time is the amount of time it takes a population to double its number. Today, the world's birth rate is almost three times its 1

2 death rate. The closer these two rates are, the slower population growth will be. Zero population growth (ZPG) is the demographic term for the state of equilibrium reached when birth and death rates are the same. Birth rate is the number of live births per thousand people. Death rate is the number of people that die per thousand people. Momentum is also a factor in population growth. Some countries, like the U.S., are growing even though the average woman has just two children. In such cases, a population can still take years to stabilize, and will do so only when the percentage of elderly people is equal to the percentage at child-bearing age. Density vs. Consumption, Space vs. Carrying Capacity "The entire world's population could fit into the state of Texas." This statement is frequently cited by people who don't understand the difference between land not currently occupied by humans and the amount and type of land required to support human life. People are only able to live in densely populated areas if enough space elsewhere is left much less densely populated. For instance, arable land must be available to grow the food for people living in cities and suburbs. Trees and other plants must be left to produce the oxygen we all need. An area's carrying capacity is the number of a given species that area can support without impairing its ability to continue supporting that population. The land within Texas could not provide enough food, water or energy to meet the needs of 6.6 billion people. It could not accommodate all the waste generated by so many either. Because that area could not come close to sustaining all of the world's people, the fact that we could all physically fit into that space is virtually meaningless. What is Overpopulation? Most people equate overpopulation with crowding, but, in fact, density is largely irrelevant to questions of overpopulation. What is relevant is carrying capacity. An area is overpopulated when its long-term carrying capacity is being degraded by its current human occupants. Degree of Impact The impact of any human group on its environment has to do with three equally important factors. The first is the number of people. The second factor encompasses the ways in which we manufacture goods, design communities and use technology. The third is the actual amount of resources consumed by each person. Unfortunately, the rate at which industrialized nations consume resources makes their populations' effect on the planet vastly greater than that of developing countries. Population growth and rapid consumption of resources are equal parts in the problem of environmental degradation. For example, the United States could reduce our consumption of resources and generation of pollution by half today. But if we did so without slowing our growth rate, the difference would be made up in 72 years, when our population is expected to double. The Environment and the Importance of Biodiversity An ecosystem will be more robust with a greater the variety of species within it. It is the biodiversity, the variety of life, on Earth that makes our survival possible. Biodiversity provides crucial "ecosystem services", such as, clean water, breathable atmosphere and natural climate control, upon which all species depend. The extermination of plant populations changes climates locally and has severe regional effects through disturbance of 2

3 the water cycle. Food, medicine and shelter are all derived from the abundant organic resources of the Earth. In fact, more than 50% of the prescription drugs dispensed worldwide are derived from wild plant species. We demand more space and resources from the Earth as human numbers grow. Taking more for people means leaving less for other species. Loss of wildlife habitat results in the extinction of countless numbers of plant and animal species every year. Currently, plant and animal species are lost every day as a result of deforestation. It is estimated that by 2015 some 6-14% of all species will have gone extinct. Doubling Time The world's current population is estimated at 6.6 billion, with an annual growth rate of 1.14 percent percent may not sound like a large number, but, at this rate, almost 77 million people will be added to the population this year. Another way to see the impact of growth rates is to consider the doubling time of a population. Doubling time for a population can be calculated by dividing 70 by the growth rate. For example, 70 divided by 1.14 is This means that if present growth rates continue, our world population would double in about 61 years. Twice as many people would need twice as much food, water, roads, houses, schools, churches, sanitation facilities, etc. Many ecologists worry that our planet can't support another doubling of population. Why are developing countries experiencing rapid population growth while developed countries are growing slowly or not at all? Both developed and developing countries have experienced significant declines in their death rates and prolonged life expectancies. Developing nations continue to have higher birth rates than developed countries. A country's birth rate is strongly linked to industrialization, economic development, availability of quality medical care, the educational level of the population and the status of women. The Industrial Revolution in Western Europe and North America improved living conditions through advances in medicine, sanitation and nutrition. These changes led to declines in death rates, especially among infants and small children. However, birth rates remained high and soon the population swelled. As these regions gradually moved away from an agricultural way of life and became more urbanized, large families became less practical and more expensive. Machinery was used more frequently to plant and harvest food reducing the need for children as farm workers. Urban families bought food instead of harvesting it. Over the course of the 19th and early 20th centuries, birth rates dropped dramatically in these areas. Developing areas, such as Africa, Latin America and parts of Asia are still primarily agriculturally based. Therefore, incentives for having larger families still exist. Technology imported from industrialized countries not only improved living conditions but caused death rates to plunge dramatically. As a result, these populations are growing rapidly. In many countries, the low status of women is another contributing factor to higher birth rates. Women are often denied educational and employment opportunities and have few alternatives to their childbearing roles. Many people wish to limit their family size but lack access to family planning education and health services. Are areas of high population density bad? No. To the contrary, urban areas hold hope for human development and protection of natural resources because they can efficiently support large numbers of people thus limiting their 3

4 impact on the natural environment. One of the reasons that cities are growing rapidly is because they offer more economic and social benefits than do rural areas. This contrasts to poorly planned areas of urban and suburban sprawl, which are fastgrowing, low-density developments typically found outside major urban areas. When sprawl attacks, it can result in a loss of green space, increased dependence on automobiles, air pollution, water pollution and a wasteful use of land resources. Don't AIDS, wars, and disease cancel out population growth? No. Our ability to reproduce is one of our species' greatest strengths. The wars of the 20th Century have accounted for the deaths of nearly 200 million people. Yet, in that time, human population has increased by 4 billion, 20 times more than those killed in wars. Similarly, other tragedies throughout history have accounted for only a small percentage of deaths worldwide. Even AIDS, which affects millions worldwide, appears only to be altering population projections in Africa, south of the Saharan Desert. There has only been one time in human history when our population growth was slowed significantly: In the 14th Century, bubonic plague, along with wars, killed an estimated one-third of the global population. Within 100 years, population was back to preplague levels. Why should the United States be concerned about its own growth? If we were only concerned about sheer numbers of people added to the population, then indeed, growth in countries such as India would be far more alarming than growth in the United States. But if we consider the impact of each person's lifestyle on the world's resources, then we reach an entirely different conclusion. U.S. consumption patterns are dramatically different from those in the developing world. Although Americans comprise only 5 percent of the world's population, we use 25 percent of its resources and produce more trash and pollution than citizens of most other nations. The average American's energy use is equivalent to the consumption of 2.5 Japanese, 6.6 Mexicans, 16.5 Chinese, 33 Indians or 121 Bangladeshis. Even moderate population growth in the U.S. spells problems for the global environment. When is the population of the United States expected to stabilize? Our population will stabilize only when the number of births plus immigrants (people coming into the country) equals the number of deaths plus emigrants (people leaving the country). It is not clear when, or even if, stabilization will occur. The United States is the third most populous country in the world and is growing by more than 3 million people each year. According to modest projections by the U.S. Bureau of the Census, the U.S. population could grow by 130 million Americans by Some people are surprised to find out that our country's population will not immediately stabilize once the total fertility rate reaches a replacement level of 2.1 (which is the growth rate for the U.S.). Due to "population momentum," our nation's population would continue to grow for another 60 to 70 years. This is because growing nations have many fewer people near the end of their lives than they have people at reproductive age. Populations would stabilize after a couple generations once those age groups have had time to balance out. Women of the World Women hold up half the sky, reads an old Chinese saying. Indeed, women have traditionally been the world s farmers, child bearers and caretakers of young and old. 4

5 Women are the backbone of families and societies. Despite their contributions to humanity, women continue to suffer from gender discrimination in much of the world. Being born female in much of the world means a lifetime as a second-class citizen. Women are denied most of the opportunities available to males in the areas of health, education, employment and legal rights. This second-class citizenship hurts the well being of women. It is also a major contributor to rapid rates of population growth in the world. Lifestyle Choices: Getting the Story on Resource Use It really wouldn t matter how many people lived on our planet if each of us didn t need resources to survive and to thrive. But since we do, we can t ignore the resource connection. For many people in the world, getting the resources they need takes up much of their day. Some have to find wood for energy. A simple neighborhood pump will save others hours of labor each day collecting water. Many people don t have the resources they need even in our own country, Some interesting facts appear when you begin to look at how the resources of our world are distributed. Most population growth in the world (over 98%) takes place in developing countries of Asia, Africa and Latin America. In industrialized countries such as the United States, Japan, or Italy, population growth is much slower, even with immigration. In some places the population is stable or declining. So surely a huge wealthy nation like ours doesn t need to worry? But wait a minute! Some argue that people in the U.S. and other industrialized countries have a much greater impact on the world s environment because of our high resources use. In other words, people here use more stuff and throw away more trash than in almost any other place in the world! What if all of the people biking to school each day in Shanghai drove a car instead? Suddenly Shanghai might start looking more like Los Angeles. And if half the people in Los Angeles could bike instead of drive? That would save a lot of gas and cut down on pollution that leads to acid rain, bad ozone and possible global warming. If we don t take care of our resources, we can t take care of ourselves. In Barbados, the beaches are kept spotlessly clean because the island s economy depends on tourists visiting the pristine sands. And in Los Angeles a family could replace their front lawn with desert plants in order to save water. If people in developing nations had affordable forms of cooking fuel available, like a solar powered stove that is becoming popular in parts of Africa, they would save time and help preserve local forests. Population and resource use impacts animals and plants as well as people. As human populations continue to grow and consume more resources, we are losing forests and driving other species towards extinction. When we start to look at population and resources together we see that our world is interconnected. Everything from the way we get to school, to the water we use for washing our faces, to what we choose to eat is all connected with decisions made by the other six billion people who share our planet. 5

6 1. What is a J curve? Write all answers in your notebook! Population Questions 2. In general, what does the J curve indicate is happening to living conditions throughout the world? Explain your answer. 3. What does the development of technology have to do with population growth rates? 4. What is zero population growth? 5. What does the term doubling time refer to? 6. Why are developing countries experiencing rapid population growth while developed countries are growing slowly or not at all? 7.Is New York City over-crowded (hint: has it exceeded its carry capacity)? Explain. 8. Why should you be concerned with growth of population in the United States when we only account for ~5% of the world s population? Matching doubling time death rate biodiversity arable land J-Curve birth rate emigrants immigrants carrying capacity overpopulated zero population growth 9.the amount of time it takes a population to double its number 10. a population curve that starts out low and skyrockets upwards 11. the number of live births per thousand people 12. the number of people that die per thousand people 13.land that can be used for growing crops 14. the number of a given species that area can support without impairing its ability to continue supporting that population 15.When the condition of any organism's numbers exceed the carrying capacity in a given area 16.variation of life forms in a given community 6

7 17. the demographic term for the state of equilibrium reached when birth and death rates are the same 18. people coming into a country 19. people leaving a country 7