Chapter 4: The Human Popula3on and the Environment http://mrspinoantl.wikispaces.com/AP+Environmental+Science#Unit %204%20Human%20Population%20and%20Impact
Basic Concepts of Popula3on Dynamics • A popula3on is a group of individuals of the same species living in the same area. • A species is all individuals that are capable of interbreeding. • Five key proper3es of any popula3on – Abundance – Birth rates – Death rates – Growth rates – Age structure
4.1 Basic Concepts of Popula3on Dynamics • Demography is the sta3s3cal study of human popula3ons. • The general study of popula3on changes is called popula3on dynamics. • How rapidly a pop changes depends on GR – Growth rate = birth rate – death rate
Age Structure • The propor3on of the popula3on at each age. – Implica3on for current and future social and economic condi3ons – Impact on the environment
Age Structure • Four general types – Pyramid-‐ popula3on w/ many young and high death rate (short average life3me) – Inverted pyramid-‐ top heavy – Column-‐ birth rate and death rate are low and a high % of pop is elderly – Column w/ a bulge-‐ event in the past caused a high birth or death rate for some age group
Age Structure
Kinds of Popula3on Growth • Exponen'al Growth – A pop increasing by a constant percentage per unit 3me.
• Human pop growth peaked at 2.1% – 1965-‐1970
• Now at 1.2%
History of Human Popula3on Growth • 1. Early period of hunter and gathers-‐ total pop < a few million • 2. Rise of agriculture-‐ allowed for increase in pop density and inc in human pop • 3. Industrial revolu3on-‐ improvements in health and food supply led to rapid inc in pop • 4. Today-‐ rate of growth slow in industrialized na3ons but high in less developed na3ons
Human Popula3on Growth
Human Popula3on Growth
Present Human Popula3on Rates of Growth • Current world popula3on >6.6 billion – With annual growth rate of 1.2%
• At this rate 84 million people added to Earth in 1 year • Correla3on between poverty and popula3on growth – Posi3ve feedback
Present Human Popula3on Rates of Growth
Current US growth rate 0.6%
Projec3ng Future Popula3on Growth • Doubling 3me (3me required for a pop to double in size) is very sensi3ve to growth rate – It changes quickly as g.r. changes – US w/ a g.r. of 0.6% has a doubling 3me of 117 yrs – Nicaragua w/ a g.r. of 2.7%, d.t. = 26 yrs – Northern Europe w/ a g.r. of 0.2%, d.t. = 350 yrs
Logis3c Growth Curve • S shaped curve – Increase exponen3ally only temporarily – Then growth rate would decline – Reach an upper pop limit @ logis3c carrying capacity (g.r. = 0)
Logis3c Growth Curve • Lifle evidence that animal popula3ons actually follow this growth curve • Involves assump3ons – Constant environment – Constant carrying capacity – Homogeneous popula3on
• Unlikely if death rate con3nue to decrease
Demographic Transi3on • Three stage pafern of change in birth rates and death rates – Occurred during the process of industrial and economic development of Western na3ons – Leads to decline in pop growth rate
Demographic Transi3on • Stage 1 – Nonindustrial country – Birth rate and death rate high, growth rate low
• Stage 2 – Period of high growth rate – W/ industrializa3on death rate declines but birth rate stays high
Demographic Transi3on • Stage 3 – Birth rate drops toward death rate – Growth rate decreases – Will take place if parents come to believe that having a small family is to their benefit.
Popula3on and Technology • Impact that all humans pose on the environment is a result of two factors – Number of people – Impact of each person on the environment
• Total impact of the human pop on enviro = average impact of an ind x total # of ind – [T = P x I]
Popula3on and Technology • Modern technology increases the use of resources and enables us to effect the enviro in new ways. – E.g. CFCs, automobiles
• Popula3on x technology reveals irony (T=P x I) – Improving standard of living increases P – Countering the benefits of declining I
Human Carrying Capacity • How many people can live on Earth at the same 3me? • Answer depends on the quality of life people desire and are willing to accept. – Es3mates vary based on assump3ons made. – “packing-‐problem” – Deep ecology
Quality of life • If people of the world were to live at the same level as those in US – High resource use – Carrying capacity would be low
• If people of the world were to live at the same level as those in Bangladesh – Poverty and heavy drain on biodiversity – Carrying capacity would be much higher
Poten3al Effects of Medical Advances on Demographic Transi3on • Second decline in death rate – Leads to Stage IV
• A second stable state would arise if birth rate then falls – Stage V
• Decision needs to be made – Stop research on diseases of old age – Reduce birth rate – Or do neither and wait for Malthus’ projec3ons
Human Death Rates • Acute or epidemic disease-‐ appears rapidly in pop, affects a large % and then declines. • Chronic disease-‐ always present in a pop, typically occurring in small % • Emerging diseases could effect both industrial and less developed na3ons – SARS – West Nile Virus – Epidemic flu
Longevity and Its Effect on Popula3on Growtrh • Maximum life3me-‐ maximum possible age to which an ind of a species can live. • Life expectancy-‐ the average # of years an ind can expect to live. – Higher in developed na3on – Japan highest, 82 years – Botswana, Lesotho and Swaziland lowest, 35 years
Each age class within a population has its own life expectancy.
Limi3ng Factors • Human popula3ons will eventually be limited by some factor or combo of factors – Short-‐term -‐ affect pop during the year in which they become limi3ng – Intermediate-‐term -‐ effects are apparent aser 1 yr but before 10yrs. – Long-‐term – effects are not apparent for 10yrs
How Can We Achieve Zero Popula3on Growth? • Simplest and one of the most effec3ve is to delay the age of 1st childbearing by women.
How Can We Achieve Zero Popula3on Growth? • Birth Control – Breast-‐feeding can delay resump3on of ovula3on – Family planning methods from abs3nence to induc3on of sterility w/ natural agents
Na3onal Programs to Reduce Birth Rates • The choice of popula3on control methods is an issue that involves social, moral and religious beliefs – Vary from country to country – Wide range of approaches • Informa3on • Accesses to birth control • Rewards and penal3es