Chapter 4: 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

• Demography 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– Impact on the environment

Age Structure

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

death rate (short average lifetime)– 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 Population Growth

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

unit time.

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

• Now at 1.2%

History of Human Population 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 revolution- improvements in health and food supply led to rapid inc in pop

• 4. Today- rate of growth 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 of the human pop on enviro = average impact of an ind x total # of ind– T = P x I

Population and Technology

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

• Population 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 time?

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

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– Stage V

• Decision needs to be made– Stop research on diseases of old age– Reduce birth rate– Or do neither and wait for Malthus’ projections

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 nations– SARS– West Nile Virus– Epidemic flu

Longevity and Its Effect on Population Growtrh

• Maximum lifetime- 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 nation– Japan highest, 82 years– Botswana, Lesotho and Swaziland lowest, 35

years

Each age class within a population has its own life expectancy.

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

National Programs to Reduce Birth Rates

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

• Information

• Accesses to birth control

• Rewards and penalties