Unit 4, Part 2: The Human Population and the Environment

Basic Concepts of Population Dynamics

• A population is a group of individuals of the same species living in the same area.

• A species is all individuals that are capable of interbreeding.

• A species is made up of populations.

Basic Concepts of Population Dynamics

• Five key properties of any population– Abundance– Birth rates– Death rates– Growth rates– Age structure

Basic Concepts of Population Dynamics

• Demographics is the statistical study of human populations.

• The general study of population changes is called Population Dynamics.

• How rapidly a pop changes depends on GR Growth rate = (birth rate – death rate)

Age Structure

• The proportion of the population at each age.– Implication for current and future social and

economic conditions - What if no one is having babies? What if 70% of the population is under age 30? (true in several countries)

– Impact on the environment - do older people have as large an impact as young people?

Age Structure

• Four general types– Pyramid- population w/ many young and high

death rate (short average lifetime)– Inverted pyramid- top heavy (Japan?)– 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 Population Growth

• Exponential Growth– A pop increasing by a constant percentage per

unit time.

• Human pop growth peaked at 2.1%– 1965-1970

• Human pop growth is now appr. 1.2%

History of Human Population Growth

• 1. Early period of hunter and gathers - the total population was < a few million (>10,000 yrs ago)

• 2. Rise of agriculture- allowed for increase in population density and increased human population

• 3. Industrial revolution - improvements in health and food supply led to rapid inc in population

• 4. Today - the rate of growth is slow in industrialized nations but high in less developed nations

Human Population Growth

Human Population Growth

Present Human Population Rates of Growth

• Current world population >6.6 billion– With annual growth rate of 1.2%

• At this rate 84 million people added to Earth in 1 year

• Correlation between poverty and population growth– Positive feedback

Present Human Population Rates of Growth

Current US growth rate 0.6%

Projecting Future Population Growth

• Doubling time (time required for a pop to double in size) is very sensitive to growth rate– It changes quickly as g.r. changes– US w/ a g.r. of 0.6% has a doubling time 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

Logistic Growth Curve

• S shaped curve– Increase exponentially only temporarily– Then growth rate would decline– Reach an upper pop limit @ logistic carrying

capacity (g.r. = 0)

Logistic Growth Curve

• Little evidence that animal populations actually follow this growth curve

• Involves assumptions– Constant environment– Constant carrying capacity– Homogeneous population

• Unlikely if death rate continue to decrease

Demographic Transition

• Three stage pattern of change in birth rates and death rates– Occurred during the process of industrial and

economic development of Western nations– Leads to decline in pop growth rate

Demographic Transition

• Stage 1– Nonindustrial country– Birth rate and death rate high, growth rate low

• Stage 2 – Period of high growth rate– W/ industrialization death rate declines but

birth rate stays high

Demographic Transition

• 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.

Population 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 (Ti) of the human population on environment = average individual impact x total # of individuals or …

• Ti = P x I

Population and Technology

• Modern technology increases the use of resources and enables us to effect the environment in new ways.– E.g. CFCs, automobiles

– Therefore we see that although technology lowers birth rates and decreases death rates, it increases the the average environmental impact per person

Human Carrying Capacity

• How many people can live on Earth at the same time?

• Answer depends on the quality of life people desire and are willing to accept.– Estimates vary based on assumptions made.

– “distribution-problem” - largely it’s a matter of where people are and how many there are in that area

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

Potential Effects of Medical Advances on Demographic Transition

• Second decline in death rate– Leads to Stage IV

• A second stable state would arise if birth rate then falls….. Leading to – Stage V

• Decision that might need to be made– Stop research on diseases of old age?– Reduce birth rate?– Wait for Malthus’ projections to come true?– Disallow “certain” people from having babies?

Human Death Rates

• Acute or epidemic diseases - appear rapidly and affect a large numbers before declining.

• Chronic disease- always present in a pop, typically occurring in small as result of long environmental exposure. (Smoking: lung cancer)

• Emerging diseases could effect both industrial and less developed nations because of long range rapid transportation– SARS– West Nile Virus– Epidemic flu (or Pandemic - H1N1 - Swine flu)

Longevity and Its Effect on Population Growth

• Maximum lifetime- maximum possible age to which an individual of a species can live.

• Life expectancy- the average # of years an individual can expect to live.– Higher in developed nation - due to availability of

sanitation and technology

– Japan highest, 82 years

– Developing nations - Botswana, Lesotho and Swaziland lowest, 35 years; notice the dramatic differential!

Limiting Factors

• Human populations will eventually be limited by some factor or combo of factors– Short-term - affect pop during the year in which

they become limiting– Intermediate-term - effects are apparent after 1

yr but before 10yrs.– Long-term – effects are not apparent for 10yrs

How Can We Achieve Zero Population Growth?

• Simplest and one of the most effective is to delay the age of 1st childbearing by women.

How Can We Achieve Zero Population Growth?

• Birth Control– Breast-feeding can delay resumption of

ovulation– Family planning methods from abstinence to

induction of sterility w/ natural agents– ONLY Zero population growth will allow for a

“sustainable” future.

National Programs to Reduce Birth Rates

• The choice of population control methods is an issue that involves social, moral and religious beliefs– Wide range of approaches

• Information• Accesses to birth control• Rewards and penalties - Canadian system example

What will our future look like?

New York City Billings, Montana