Botkin & Keller Environmental Science 5/e Chapter 4 The Human Population and the Environment

Botkin & KellerEnvironmental Science 5/e

Chapter 4

The Human Population and

the Environment


Basic Concepts of Population Dynamics

• Population:– A group of individuals of the same species living in

the same area of interbreeding and sharing genetic information.

• Species:– All individuals that are capable of interbreeding.– Made up of populations

• Population dynamics– The general study of population changes.


Age Structure

• Population age structure:– The proportion of the population in each age

class– Affects current and future birth rates, death

rates and growth rates– Has an impact on the environment– Has complications for current and future

social and economic status.


Forecasting Population Change

• Formula to represent population change:

P2 = P1 + (B – D) + (I – E)


Fig 4.3

© 2005 John Wiley and Sons Publishers


A Brief History of Human Population Growth

1. Hunters and gatherers• The world’s population was probably less than a few million

2. Early, pre-industrial agriculture• Allowed a much greater density of people• The first major increase in human population

3. Machine age• Industrial revolution led to rapid increase in human population

4. The Modern era• Rate of population has slowed in wealthy nations but

continues to increase rapidly in poorer, less developed nations.


Fig 4.4a



Fig 4.4b



Fig 4.4c



Fig 4.5



Fig 4.6



Projecting Future Population Growth

• Exponential growth and doubling time• The logistic growth curve

– “S” shaped curve that is generated by the logistic growth equation.

• A small population grows rapidly• But the growth rate slows down• The population eventually reaches a constant size.

• Logistic carrying capacity– The population size at which births equal deaths and

there is no net change in population


Fig 4.7



Fig 4.8



The Demographic Transition

• 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 a decline in population growth.

Stage I: Decline in death rateStage II: High growth rateStage III: Birth rate drops toward the death rate,

leading to low or zero growth rate.


Fig 4.9



Population and Technology

• The total impact of the human population on the environment is:– the average impact of an individual multiplied

by the total number of individuals

T = P x I


The Human Population, the Quality of Life, and the Human Carrying Capacity

• Human carrying capacity– The number of people that can live on Earth at the

same time?– To determine:

1. Extrapolate from past growth

2. The “Packing Problem” approach– Considers how many people might be packed onto Earth,

not taking into sufficient account the need for lands and oceans to provide food, water, energy, construction materials, and scenic beauty and the need to maintain biological diversity


Human Death Rates and the Rise of Industrial Societies

Acute or epidemic diseaseAppears rapidly in the population,Affects a comparatively large percentage of it,Declines then almost disappears, only to reappear

later

Chronic disease Is always present in a populationTypically occurs in a relatively small but relatively

constant presentation of the populationExamples include heart disease, cancer, and stroke


Fig 4.10



Longevity and its Effect on Population Growth

• Maximum lifetime:– The genetically determined maximum

possible age to which an individual of a species can live

• Life expectancy:– The average number of years an individual

can expect to live given the individual’s present age


Limiting Factors

1. Short-term factors• Those that affect a population during the year in

which they become limiting

2. Intermediate-term factors• Those whose effects are apparent after one year

but before ten years

3. Long-term factors• Those whose effects are not apparent for ten years

Some factors fit into more than one category


Fig 4.11



How Can We Achieve Zero Population Growth?

• Delay the age of first childbearing by women• Birth control

– Biological and Social• Breast-feeding, which can delay resumption of ovulation• Abstinence• Induction of sterility with natural agents• Contraceptive devices

– National Programs to Reduce Birth Rates• Formal family planning programs to

– explain the problems arising from rapid population growth– Describe the benefits to individuals of reduced population

growth.

Documents

Botkin & Keller Environmental Science 5/e Chapter 4 The Human Population and the Environment