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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