Human Population And 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.

Chapter 4

• Species:

The Human Population and the Environment

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

• Population dynamics – The general study of population changes.

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Age Structure

Forecasting Population Change

• 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.

• Formula to represent population change: P2 = P1 + (B – D) + (I – E)

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Fig 4.3

A Brief History of Human Population Growth 1.

Hunters and gatherers •

2. • •

3. 4.

Industrial revolution led to rapid increase in human population

The Modern era •

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Allowed a much greater density of people The first major increase in human population

Machine age •

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The world’s population was probably less than a few million

Early, pre-industrial agriculture

Rate of population has slowed in wealthy nations but continues to increase rapidly in poorer, less developed nations.

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Fig 4.4a

Fig 4.4b

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Botkin & Keller Environmental Science 5/e

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Fig 4.4c

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Fig 4.5

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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; growth rate slows down • Population eventually reaches a constant size; • Until the ‘inflection point’ is reached, we can’t project the final logistic size

• Logistic carrying capacity – The population size at which births equal deaths and there is no net change in population Botkin & Keller Environmental Science 5/e

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Fig 4.7

Fig 4.8

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© 2005 John Wiley and Sons Publishers

© 2005 John Wiley and Sons Publishers

Fig 4.9

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 rate Stage II: High growth rate Stage III: Birth rate drops toward the death rate, leading to low or zero growth rate. Botkin & Keller Environmental Science 5/e

Botkin & Keller Environmental Science 5/e

Population and Technology

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

• 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=PxI

•

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 –

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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 Botkin & Keller Environmental Science 5/e

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Fig 4.10

Human Death Rates and the Rise of Industrial Societies Acute or epidemic disease
Appears 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 population
Typically occurs in a relatively small but relatively constant presentation of the population
Examples include heart disease, cancer, and stroke Botkin & Keller Environmental Science 5/e

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Longevity and its Effect on Population Growth

Limiting Factors

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1. Short-term factors

• Maximum lifetime: – The genetically determined maximum possible age to which an individual of a species can live

•

2. Intermediate-term factors •

• Life expectancy: – The average number of years an individual can expect to live given the individual’s present age

Those that affect a population during the year in which they become limiting 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

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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. Botkin & Keller Environmental Science 5/e

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