The Human Population and the Environment Basic Concepts

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 average environmental impact 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 - H 1 N 1 - 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 10 yrs. – Long-term – effects are not apparent for 10 yrs

How Can We Achieve Zero Population Growth? • Simplest and one of the most effective is to delay the age of 1 st 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