HUMAN POPULATION & ENVIRONMENT

Transcription

1 HUMAN POPULATION & ENVIRONMENT Population Dynamics Human Growth, and carrying capacity of the earth Human impact on Environment What is Population Dynamics A species is all individuals that are capable of interbreeding, and so a species is composed of one or more populations. A population is a group of individuals of the same species living in the same area or interbreeding and sharing genetic information. Population dynamics is the general study of population changes. Demography is the statistical study of human populations, and people who study the human population include demographers. 1

2 What is Population Dynamics Five key properties of any population are Abundance Birth rates Death rates Growth rates Age structure Definition of certain population parameters Total Fertility Rate: the average number of children each woman has over her lifetime. Replacement-level Fertility: a fertility rate that will replace just the mom and dad, theoretically 2.0. Mom has 2 kids, so when mom and dad both die 2 additional people (the offspring) will take their place; the population is stable. Less than 2.0 the population declines; Greater than 2.0 the population increases. 2

3 POPULATION DYNAMICS AND CARRYING CAPACITY Most populations live in clumps although other patterns occur based on resource distribution. Changes in Population Size Populations increase through births and immigration Populations decrease through deaths and emigration What is the difference between immigration and emigration? 3

4 Age Structure: Young Populations Can Grow Fast How fast a population grows or declines depends on its age structure. Pre-reproductive age: not mature enough to reproduce. Reproductive age: those capable of reproduction. Post-reproductive age: those too old to reproduce. Limits on Population Growth: Biotic Potential vs. Environmental Resistance No population can increase its size indefinitely. The intrinsic rate of increase (r) is the rate at which a population would grow if it had unlimited resources. r=( N/ t)/n The value of r indicates whether a population is growing (r > 0) declining (r < 0) zero population growth (ZPG) ( r = 0), Births and deaths still occur, but they balance exactly. Carrying capacity (K): the maximum population of a given species that a particular habitat can sustain indefinitely without degrading the habitat. N/ t = rn({k-n}/k) N = number of individuals in a population N/ t = change in number per time r = increase in numbers of individuals per time period per individual K = carrying capacity K-N/K = a measure of environmental resistance. (N vs carrying capacity). 4

5 Number of reindeer 10/25/2017 Exponential and Logistic Population Growth: J-Curves and S-Curves Populations grow rapidly with ample resources, but as resources become limited, its growth rate slows and levels off. As a population levels off, it often fluctuates slightly above and below the carrying capacity. Environmental Resistance Carrying capacity (K) Biotic Potential Exponential Growth Time (t) Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size Members of populations which exceed their resources will die unless they adapt or move to an area with more resources. Population overshoots carrying capacity Population Crashes Carrying capacity Year 5

6 Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size Over time species may increase their carrying capacity by developing adaptations. Some species maintain their carrying capacity by migrating to other areas. So far, technological, social, and other cultural changes have extended the earth s carrying capacity for humans. Population Density and Population Change: Effects of Crowding Population density: the number of individuals in a population found in a particular area or volume. A population s density can affect how rapidly it can grow or decline. e.g. biotic factors like disease Some population control factors are not affected by population density. e.g. abiotic factors like weather 6

7 Types of Population Change Curves in Nature Population sizes may stay the same, increase, decrease, vary in regular cycles, or change erratically: Stable: slightly fluctuates above and below carrying capacity. Irruptive: populations explode and then crash to a more stable level. Cyclic: populations fluctuate and regular cyclic or boom-andbust cycles. Irregular: erratic changes possibly due to chaos or drastic change. Types of Population Change Curves in Nature Population sizes often vary in regular cycles when the predator and prey populations are controlled by the scarcity of resources. 7

8 REPRODUCTIVE PATTERNS Some species reproduce without having sex (asexual). Offspring are exact genetic copies (clones). Others reproduce by having sex (sexual). Genetic material is mixture of two individuals. Disadvantages: males do not give birth, increase chance of genetic errors and defects, courtship and mating rituals can be costly (Courtship rituals consume time and energy, can transmit disease, and can inflict injury on males of some species as they compete for sexual partners) Major advantages: genetic diversity, offspring protection. Reproductive Patterns: Opportunists and Competitors Large number of smaller offspring with little parental care (rselected species). Fewer, larger offspring with higher invested parental care (K-selected species). r-selected species tend to be opportunists while K-selected species tend to be competitors. r species; experience r selection Carrying capacity Time K species; experience K selection K 8

9 Reproductive Patterns r-selected Species 1. Many small offspring 2. Little or no parental care and protection of offspring 3. Early reproductive age 4. Most offspring die before reaching reproductive age 5. Small adults 6. Adapted to unstable climate and environmental conditions 7. High population growth rate (r) 8. Population size fluctuates wildly above and below carrying capacity (K) 9. Generalist niche 10. Low ability to compete 11. Early successional species K-Selected Species 1. Fewer, larger offspring 2. High parental care and protection of offspring 3. Later reproductive age 4. Most offspring survive to reproductive age 5. Larger adults 6. Adapted to stable climate and environmental conditions 7. Lower population growth rate (r) 8. Population size fairly stable and usually close to carrying capacity (K) 9. Specialist niche 10. High ability to compete 11. Late successional species Survivorship Curves: Short to Long Lives The way to represent the age structure of a population is with a survivorship curve. The populations of different species vary in how long individual members typically live. I. Late loss population live to an old age. II. III. Constant loss population die at all ages. Most members of early loss population, die at young ages. 9

10 Age Distribution Age-Structure Diagram shows growth patterns of populations grouped into categories Horizontal axis = Number of individuals Human Population Rapid Growth The most dramatic increase in the history of the human population occurred in the last part of the 20th century and continues today into the early 21st century. As mentioned, in merely the past 40 years the human population of the world more than doubled, from 2.5 billion to about 7 billion. 10

11 Global human population growth Now it is almost 7 billion humans living on this planet So what.?????? Discussion point!!!!! Human Population Growth, and Carrying Capacity of the Earth But important questions remain: Do we have a human population problem? Is overpopulation at the root of all environmental problems? Can the population be controlled? What strategies exist to keep population in check, and will these measures help the environment? 11

12 Population (N) 10/25/2017 Human Population Growth is Exponential Standard exponential growth curve: r = intrinsic growth curve - based on individual species growth potential dn dt r N Time (T) Exponential Curve (continued) Growth is very slow at first, but as the population increases over time the growth rate becomes enormous Question: mathematically, where does this curve go to? Infinity! Is this possible? Of course not. Usually there is some restriction on population growth, whether it be reduced resources, diseases, etc. In the real world, populations level off around a carrying capacity. Carrying Capacity: the maximum number of individuals that the environment can support Usually set by the amount of available resources 12

13 Population (N) 10/25/2017 Carrying Capacity The carrying capacity has a dampening function that limits a population once numbers grow to a certain value. As N approaches K, growth declines to zero (K-N) K = carrying capacity Dampening function dn rn ( K N ) dt K Time (T) History of Human Populations Prior to ca. 10,000 years ago human population growth was very slow (similar to the hummingbird). Then about 10 8 thousands years ago, human population growth increased Note: the last 100 years have witnessed the greatest increase in human populations (Chiras, Environmental Science: Creating a sustainable future, 6 th Edition, Jones and Bartlett, Sudbury, MD, pg

14 Human Population Estimates for human population at 1750 are around 800 million people. World population reached 1 billion for the first time in What happened around the mid Eighteen century to explain dramatic rise in population? The Industrial Revolution was another technological advancement that had an effect on human population. Why? Increased birth rate (demand for labor may have contributed to the increase in population the increase was market-driven) Human Population: overall trend Most of the World s population growth has occurred in the last 100 years or so. The World s population reached 2 billion in 1930, only 100 years since From ,, population went from 2 billion to 6 billion, which is unprecedented in human history. The dramatic rise in population is a result of several factors: Better healthcare and medicine Better nutrition and sanitation practices Increase in food production In short, technological advances in just about every field has contributed 14

15 Human Population Values Year (T) 1 AD ,000 Human Population (N) # yrs to add an additional billion people billion billion 100 years billion 30 years billion 15 years billion 12 years billion 12 years (2050) 8.9 billion Note the growth rate is slowing down Human Population Note the rapid increase in the growth rate. It is taking less time to add an additional 1 billion persons. 15

16 Human Population: overall trend In recent years, though, population growth has slowed. The rate of increase is slowing The time to add 1 billion people is decreasing, but the amount of the decrease is becoming less and less. For example, the human population went from 2 billion to 3 billion in 30 years ( ). Population went from 3 billion to 4 billion in 15 years ( ). Population increased from 4 billion to 5 billion in 12 years ( ). Population increased from 5 billion to 6 billion in 12 years; this is the same rate of increase as the 4 5 billion. Even though the rate of population increase is lessening, be cognizant that the overall number of people is still expanding. World Population growth, rate and absolute growth Human population numbers are increasing, but the growth rate is declining. Are we reaching carrying capacity????? 16

17 Human Population Growth and The Environment The increase in human populations is an environmental concern for several reasons; these are just a few: 1) more waste 2) use more resources 3) increased land development for both agriculture and habitation 4) more energy demands 5) greater pressure on wildlife and greater pressure on marine life It is suggested, that human population growth is the biggest threat to the environment Human population growth may possibly be the greatest threat to humans themselves!!!! Human Population Growth and carrying capacity Once populations numbers = k, the growth rate drops. If the population increases too fast and the numbers exceed K, the amount of available resources plummet and the population crashes. The questions will be: What is the human carrying capacity? How many people will the World support? Have we already exceeded K, If so, are we susceptible to a major population crash? 17

18 Different Worlds Human population growth is not the same globally. One of the greatest factors influencing population is the economic status of a nation or region. based on their economic status, it is possible to define three types of countries: 1. High-income, industrialized (developed) countries (e.g. US, Canada, Japan, UK, France). 2. Middle-income/ moderately developed (e.g. Russia, eastern Europe, Mexico, Costa Rica) 3. Low-income, developing countries (e.g. Nicaragua, Angola, Ethiopia). Different Worlds There are many disparities between the high-income (HI) and low-income (LI). HI make up 16% of the World s population but control about 81% of the wealth (GNP) LI make up 41% of the World s population but control only 3.4% of the wealth (GNP) 18

19 Table of Population Data for Selected Countries Note the relationship between development status and total fertility rate. Table of Population Data for Selected Countries Note the US is the only developed country that has a TFR capable of increasing (maintaining) the population. Actually, some estimates for US TFR are closer to 3 19

20 Population increase in Developed and Developing Countries This figure illustrates this population explosion, sometimes referred to as the population bomb. It shows that the expected decrease in population in the developed regions is more than offset by rapid population growth in the developing regions Discussion point!!!!! Paul Ehrlich s published The Population Bomb in 1968: One of the original accusations that any environmental issue is really just a human overpopulation issue. Every environmental problem is directly related to there being too many people. The way to help the environment, is to control over population. What is your opinion!!!??? 20

21 The Ecological Footprint The Ecological Footprint is the environmental impact of a person or population It is the amount of biologically productive land & water It is for raw materials and how to dispose or recycle waste Overshoot: humans have surpassed the Earth s capacity We are using 30% more of the planet s resources than are available on a sustainable basis! Overshoot The world s ecological deficit is referred to as global ecological overshoot. Since the 1970s, humanity has been in ecological overshoot, with annual demand on resources exceeding what Earth can regenerate each year. Today humanity uses the equivalent of 1.6 Earths to provide the resources we use and absorb our waste, according to Global Footprint Network. This means it now takes the Earth one year and six months to regenerate what we use in a year. We use more ecological resources and services than nature can regenerate through overfishing, overharvesting forests, and emitting more carbon dioxide into the atmosphere than forests can sequester. 21

22 In 2008, the Earth s total biocapacity was 12.0 billion gha, or 1.8 gha per person, while humanity s Ecological Footprint was 18.2 billion gha, or 2.7 gha per person. This discrepancy means it would take 1.5 years for the Earth to fully regenerate the renewable resources that people used in one year, or in other words, we used the equivalent of 1.5 Earths to support our consumption. Ecological footprints are not all equal The ecological footprints of countries vary greatly The U.S. footprint is almost 5 times greater than the world s average Developing countries have much smaller footprints than developed countries 22

23 The environmental impact is related to human population!! Ehrlich and Holdren propose that the environmental impact is related to human population and the varying degrees of pressure different people put on the environment. Their premise is that the more affluent countries, even though they are smaller in population, have more of an affect on the environment because they use substantially more resources. Thus, in this case, human population differences between developed and developing nations may not be the sole reason for environmental degradation. The environmental impact is related to human population!! As mentioned it is hypocritical to criticize developing countries for continuing to grow their populations. Those who live in wealthy, but population-stable, developed countries are equally guilty of environmental misuse. The US for example has 5% of the population but is currently responsible for 24% of the total global emissions of CO2. The US, then, has a lager Ecological footprint than other developing countries. 23

24 Population Growth By Age Structure In predicting future population trends, it is important to look at population growth by age group. For example, looking at the age structure of a population, whether the bulk of the population is older or younger, can provide insight into future population numbers. This relationship is displayed in population profiles, which is a bar graph showing the number or proportion of people at each age for a given population. Comparison of Population Profiles: Developed vs. Developing Countries Developed countries Less-developed countries 24

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26 Population & consumption Human population growth exacerbates يفاقم all environmental problems The growth rate has slowed, but we still add more than 200,000 people to the planet each day Our consumption of resources has risen even faster than our population growth. Life has become more pleasant for us so far However, rising consumption amplifies the demands we make on our environment. Why so many humans? Agricultural revolution Stable food supplies More food Industrial revolution Urbanized society powered by fossil fuels Sanitation and medicines (health) Transportation and Communication 26

27 Humans and the world around us Humans change the environment, often in ways not fully understood We depend completely on the environment for survival Increased wealth, health, mobility, leisure time But, natural systems have been degraded i.e., pollution, erosion and species extinction Environmental changes threaten long-term health and survival Environmental science is the study of: How the natural world works How the environment affects humans and vice versa Natural resources: vital to human survival Renewable resources: Perpetually available: sunlight, wind, wave energy Renew themselves over short periods: timber, water, soil These can be destroyed Nonrenewable resources: can be depleted Fossil Oil, coal, minerals Natural resources = substances and energy sources needed for survival 27

28 Discussion points: What do you Think about human population impact on the environment?? Facts about human population Humans are part of the Earth's ecosystem. Human activities can either deliberately or inadvertently alter the balance of an ecosystem. How do human activities affect the environment? Human impacts on the Environment Global warming Use of machinery by humans seems to be increasing CO2 levels in the air. CO2 prevents heat from escaping, causes slight world wide temperature increases Rising water temperatures causes coral bleaching 28

29 Human impacts on the environment Deforestation Caused by demand for wood products, need for space, farmland, housing, roads Deforestation causes habitat fragmentation Animals and plants are forced into confined areas Habitat Fragmentation 29

30 Human impacts on the Environment Ozone depletion Caused by aerosol chemicals called chlorofluorocarbons (CFCs) CFC s Escape into atmosphere, reacts breaking down the ozone (O3, a protective atmospheric layer) UV rays penetrate the atmosphere and cause harm to many organisms 30

31 Human impacts on the Environment Fishing activities Demand for fish and shellfish Commercial Fishing be harmful to environment in many ways Human impacts on the environment Invasive species (EXOTIC SPECIES) Introduced by people accidentally or intentionally Can cause problems if no natural enemies are present Cane toad was introduced to Australia to control cane beetles, pest insects that destroy sugar cane crops 31

32 Human impacts on the Environment Exotic pet trade Capture and sell wild animals from exotic locations Wealthy buyers and collectors desire obscure animals Animals removed from their habitat causes an imbalance in the ecosystem Human impacts on the Environment: Agricultural DDT Fertilizers Animal wastes (nitrogen) Pollution Homes Strong cleaning agents Industry Toxic gases and wastes Acid rain 32

33 We face challenges in agriculture Expanded food production led to increased population and consumption It s one of humanity s greatest achievements, but at an enormous environmental cost Nearly half of the planet s land surface is used for agriculture Chemical fertilizers Pesticides Erosion Changed natural systems Importance of the Environment Natural resources: Non-renewable includes fossil fuels (petroleum, coal) Renewable includes animals, plants, water, wind, etc. Even renewable resources can run out Renewable energy sources include wind power, geothermal energy, ocean currents 33

34 Discussion point? Can we continue to expand the earth's carrying capacity for humans? No. Unless humans voluntarily control their population and conserve resources, nature will do it for us. Yes. New technologies and strategies will allow us to further delay exceeding the earth's carrying capacity. Moodle- Self reading The Demographic Transition According to the population profiles, developing countries will continuously expand. Then, is there any hope for decreasing the population growth? Perhaps through the Demographic Transition (DT). The Demographic Transition is a three-stage pattern of change in birth rates and death rates that has occurred during the process of industrial and economic development of Western nations. It leads to a decline in population growth. 34

35 The Demographic Transition I. A decline in the death rate while birth rate still high II. A decline in both birth and death rates III. The birth rate drops toward the death rate, and the growth rate therefore declines, eventually to a low or zero growth rate. Stage I &II A decline in the death rate is the first stage of the demographic transition. In a non industrial country, birth rates and death rates are high, and the growth rate is low. With industrialization, health and sanitation improve and the death rate drops rapidly. The birth rate remains high, however, and the population enters Stage II, a period with a high growth rate. Most European nations passed through this period in the 18 th and 19th centuries. 35

36 Stage III As education and the standard of living increase and as familyplanning methods become more widely used, the population reaches Stage III. The birth rate drops toward the death rate, and the growth rate therefore declines, eventually to a low or zero growth rate. However, the birth rate declines only if families believe there is a direct connection between future economic well-being and funds spent on the education and care of their young. Such families have few children and put all their resources toward the education and well-being of those few. Many of the Developing countries would remain in stage II with lowered death rate but stable fertility. Populations in this case would continue to rise, perhaps acting in a negative feedback loop. 36

37 Stage III Historically, parents have preferred to have large families. Without other means of support, aging parents can depend on grown children for a kind of social security, and even young children help with many kinds of hunting, gathering, and lowtechnology farming. Unless there is a change in attitude among parents unless they see more benefits from a few well-educated children than from many poorer children nations face a problem in making the transition from Stage II to Stage III. Stage III Some developed countries are approaching Stage III, but it is an open question whether developing nations will make the transition before a serious population crash occurs. The key point here is that the demographic transition will take place only if parents come to believe that having a small family is to their benefit. Here we again see the connection between science and values. Scientific analysis can show the value of small families, but this knowledge must become part of cultural values to have an effect 37

38 Thomas Malthus and human population Thomas Malthus Population growth must be restricted, or it will outstrip food production Starvation, war, disease Neo-Malthusians Population growth has disastrous effects Paul and Anne Ehrlich, The Population Bomb (1968) Malthus: Human population growth is exponential but agricultural growth is arithmetic. Eventually population would outstrip the available resources. Eventually the power of humans to reproduce would be more powerful than the ability of the Earth to sustain it overpopulation 38

39 Garrett Hardin s Tragedy of the Commons Unregulated exploitation leads to resource depletion Soil, air, water Resource users are tempted to increase use until the resource is gone Solution? Private ownership? Voluntary organization to enforce responsible use? Governmental regulations? 39