Chapter 5

The Human Population

POPULATION BIOLOGY From Raven & Berg – Chapter 8

Principles of Population Ecology

• The size of the human population is central to many environmental problems and their solutions– Important that we understand how populations

increase or decrease– Population – a group of organisms of the same

species that live in the same geographical area at the same time

Population Ecology

• Deals with the number of individuals of a particular species that are found in an area and how and why those numbers increase or decrease– Population ecologists try to determine the

population processes that are common to all populations• Which we will apply to chapter 5 in our text book

(Human Populations)

Aspects of Population Ecology

• Study how a population competes for food or other resources

• How predation, disease, and other environmental pressures affect the population

• Reproductive success or failure

Maximum Population Growth

• The maximum rate at which a population could increase under ideal conditions is known as its biotic potential, or intrinsic rate of increase.

• Different organisms have different biotic potentials

Factors That Affect Biotic Potential

• Age at which reproduction begins – Reproducing earlier in life has the greatest effect

on biotic potential• Duration of when organism is capable of

reproduction• Number of reproductive periods per lifetime• Number of offspring produced during each

period of reproduction– Factors are called life history characteristics

Reproductive Strategies

• r – selected species– Have traits that contribute to a high population

growth rate• (r designates growth rate)

– Small body size, early maturity, short life span, large broods, and little or no parental care are typical of many r strategists

– Usually opportunists, found in variable, temporary, or unpredictable environments

– Probability of long term survival is low

Reproductive Strategies

• K – selected traits– Traits maximize the chance of surviving in an

environment where the number of individuals (N) is near the carrying capacity (K) of the environment.• Do not produce large numbers of offspring• Have long life spans with slow development• Late reproducing• Large body size• Typically invest in parental care of their youngsters

Survivorship

• Ecologists construct life tables for plants and animals that show the likelihood of survival for individuals at different times during their lives.

• Survivorship is the probability that a given individual in a population will survive to a particular age

Type III Survivorship

• The probability of death is greatest early in life• Those individuals that avoid death,

subsequently have a high probability of survival– Characteristic of many fish species and oysters

Type III Survivorship

Type II Survivorship

• Intermediate between types I and III. • Probability of death is likely across all age

groups– Results in a linear decline in survivorship• This results from the essentially random

events that cause death with little age bias–This curve is rare, some lizards have a

type II survivorship

Type II Survivorship

Type I Survivorship

• Exemplified by humans and elephants• The young (pre-reproductive) and those at

reproductive age have a high probability of living

• Probability of survival decreases more rapidly with increasing age– Deaths are concentrated later in life.

HUMAN POPULATION EXPANSION AND ITS CAUSES

5.1

Warm-Up

• Define chapter 5 vocabulary terms. Vocab quiz Wednesday – Fertility– Replacement level fertility– Demography– Population profile– Graying– Demographic Transition

• Phase I, II, III, IV

– Crude death rate– Crude birth rate– Doubling time– Rule of 70

History

• Considering the thousands of years of human history, the recent rapid expansion of the global population is a unique event

• From the dawn of human history until the beginning of the 1800s population increased slowly

• It was roughly 1830 before the world population reached 1 billion

History

• By 1930, the population had doubled to 2 billion• 1975 – 4 billion• 1987 – 5 billion• 1999 – 6 billion– Currently growing at the rate of 76 million people

added a year– Based on current information, medium projection

predicts the world will pass 7 billion in 2012• 8 billion – 2024• 9 billion - 2047

Reasons for Patterns of Growth

• Flow/fluctuating growth wad due to the prevalence of diseases

• High reproductive rates were balanced with a high infant mortality rate– High birth rate and death rate causes slow

population growth

Breakthroughs

• Late 1800s– Louis Pasteur discovered diseases were caused by

infectious agents• Organisms transmitted by food, insects, water, rodents

• Vaccinations were developed• Cities and towns began treating driving water• Discovery of penicillin in the 1930s• Improvements in nutrition

Declines

• 1960s – growth rate peaked at 2.1% increase a year

• Declines result of decline in total fertility rates– Average number of babies born to a woman over

her lifetime• In 1960s fertility rate was an average of 5.0 children per

woman• Present value 2.7 children per woman

UN Population Projections

• Demonstrate role played by fertility assumptions– Constant projection – 2.6 children– Medium projection – assumes decline in fertility

rate in developing countries (2.02/woman)– High projection – assumes fertility rates ½ child

greater than the Medium projection– Low projection – assumes fertility rates ½ child

less than Medium projection

DIFFERENT WORLDS5.2

Rich Nations, Poor Nations

• The World Bank, and arm of the United Nations, divides the countries of the world into three main economic categories according to average per capita gross national income

High Income, Highly Developed, Industrialized Countries

• 971 million in 2003• Includes the U.S., Canada, Japan, Korea,

Australia, New Zealand, the countries of western Europe and Scandinavia, Singapore, Taiwan, Israel, and several Arab states– 2003 gross national income per capita• $9,386 and above; average of $28,550

Middle Income, moderately developed countries

• 3 billion in 2003• Countries of Latin America, northern and

southern Africa, China, Indonesia and other southeastern Asian countries, many Arab states, eastern Europe and countries of the former U.S.S.R

• 2003 gross national income per capita ranges from $755 to $9,385; average of $1,920

Low-Income, Developing Countries

• 2.3 billion• Comprises the countries of eastern, western,

and central Africa, India, and other countries of Asia, and a few former Soviet republics

• 2003 gross national income per capita is less than $766– Average of $450

Disparities

• High income countries make up 15% of world’s population– Control 80% of the worlds wealth• (calculated on the basis of gross national income)

• Low income countries make up 37% of the world’s population– Control only 3% of the worlds wealth• Amounts to a difference in per capita income of 63:1!

Human Development Index

• United Nations Development Program (UNDP)• Measures general well-being based on more

info about literacy, and living standards– Makes a more direct measurement of poverty in

both LDC and MDC

Dimensions of the Human Poverty IndexBased on information about life expectancy, literacy, and living standards

Population Growth In Rich and Poor Nations

• More than 98% of the world population growth is occurring in the developing countries– 2006 growth rate developed countries – 0.1%• Add less than 1 million to the worlds population in a

year

– 2006 growth rate in developing countries – 1.5% • Adding 75 million in a year

Fertility

• Population growth occurs when births outnumber deaths– Total fertility rate• average number of children each woman in a

population has over her lifetime

– Replacement level fertility• Fertility rate that will just replace the population of the

parents– 2.1 in developed countries, higher in developing countries

which have higher infant/childhood mortality rates

Population Increase in Developed and Developing Countries

Because of higher birthrates, developing countries represent a larger and larger share of the world’s population

Different Population, Different Problems

• Ecologists Paul Ehrlich and John Holdren proposed a formula to account for the human factors that contribute to environmental deterioration and the depletion of resources– Human pressure on the environment was product

of three factors• Population, affluence, technology

IPAT formula

• I = P * A * T• Environmental Impact (I) is proportional to

population (P) multiplied by affluence and consumption patterns (A), and multiplied by the level of technology of the society (T)

Demand vs. Need

• Most environmental issues are a result of the high consumption associated with affluent lifestyles in developed countries– U.S – 5% of worlds population, 24% of global

emissions of CO2• Developing countries needs include economic

growth, more employment, wise leaders, effective public polices, fair treatment by other nations, technological and financial help

Stewardship

• Developed countries must address issues to achieve sustainability

• IPAT formula might be modified to• I = P * A * T

S S stands for stewardly concern and practice

CONSEQUENCES OF POPULATION GROWTH AND AFFLUENCE

5.3

Developing Countries

• Prior to industrial revolution most human population survived through subsistence agriculture– Families lived on the land, raised livestock,and

produced enough crops for their own consumption

Rural Populations

• 70% of the world’s poor live in rural areas• Most are engaged in small-scale agriculture• Environmental impacts on population growth

of this sect of the population

1. Land Reform

• Reform system of land ownership• Collectivization and ownership by the wealthy

are two patterns of agriculture land ownership that have kept rural peoples in poverty

2. Intensifying Cultivation

• Introduction of more highly productive varieties of basic food grains– Beneficial effect in supporting growing population– Consequences• Working the land harder, increasing intensity of grazing

– Deterioration of soil, decreased productivity, erosion, desertification

3. – Opening New Lands for Agriculture

• Means converting natural ecosystems to agricultural production– Losing the goods and services those ecosystems

were contributing• Most of the time the ecosystem converted isn’t suited

for agriculture and requires large inputs of water and fertilizer

Deforestation in the TropicsMillions of acres of rain forest in Central and South America are being cut down each year to make room for agriculture. Much of this deforestation is done by poor, young people who are seeking an opportunity to get ahead but are untrained and unskilled in the requirements of maintaining tropical soil

4. – Illicit Activities

• People without the money to grow or buy food will resort to desperation

5. – Emigration and Immigration

• Low-income country residents believe they can improve their situation by migration to wealthier countries

• Also immigration occurs to escape civil wars and ethnic persecution

Problems with Immigration

• Prejudice against foreigners • Refugee camps– Diseases and hunger take toll on human life

6. – Migration to Cities

• Move from countryside in search of employment and a better life

• Most of the net growth of the next 50 years in the developing countries will be absorbed in urban areas

Growing CitiesTop 10 world metropolitan areas in 2005.

SlumsOn the outskirts of Sao Paulo, Brazil. 32% of the cities population lives in these blighted areas

Affluence• America leads the world in consumption of many

resources– Largest share of aluminum, coffee, corn, lead, oil,

oilseeds, natural gas, rubber, tin, and zinc– Lead in per capita consumption of meat, paper

(725 lbs of paper/year!)• Affluence provides benefits such as providing

amenities such as safe drinking water, sanitary sewage systems, collection and disposal of refuse– Keeps many forms of pollution in check

The Dark Side

• Because the U.S. consumes so many resources, we also lead the world in production of many pollutants

Negative Aspects of Affluence

• Worlds wealthiest 20% is responsible for 86% of all private consumption and 80% of world trade– Consequences

• 11 of the 15 major fisheries are exploited• Old-growth forests are being cleared in South America• Oil spills “by-product” of oil appetite • Tropical rain forests being cleared for exotic wood• Metals mined• Oil extracted

– ALL IN DEVELOPING COUNTRIES FAR AWAY FROM COUNTRIES USING RESOURCES!

DYNAMICS OF POPULATION GROWTH

5.4

Demographics

• Demography– Study of collecting, compiling, and presenting

information about human population• Must consider more than just increase in numbers• Must also consider how the number of births ultimately

affects entire population over the longevity, or lifetimes, of the individuals

Population Profiles

• Bar graph showing the number or proportion of people (males and females separately) at each age for a given population– Data is collected through a census– In U.S. an most other countries a census is taken

every 10 years

– FYI – I may also refer to these bar graphs as POPULATION PYRAMIDS in class

Age Profile for the U.S.

• Shoes the age structure of the population• Proportion of people in each age group at a

given date– Different cohorts

Boom or Bust?

• 1931 -1935 – Low fertility rate due to Great Depression

• 1946-1960– “Baby boom”

• Reflection of returning veterans flowing WWII

• 1961-1976– Decline in fertility rates

• People choose to have fewer children • “baby bust”

• Rise in people born in more recent years is “baby boom echo”

The changes in fertility led to the baby boom and baby bust in the U.S. The rate now hovers about the replacement level

Planning Tool

• Population profile provides a means of planning for future demands on goods and services

• Social Security– Will become big issue as baby boomer generation

retires

Future populations

• Current population growth is calculated from three vital statistics– Births– Deaths– Migration

• 2005 statistics – U.S. – 4.18 million births, 2.44 million deaths, 946 thousand

immigrants• 35% increase was due to migration• 65% due to natural increase

Future Populations

• Demographers can only make projections– Assumptions about fertility, mortality, and

migration

Projections for Developing Countries

• Ex – Italy• Population “graying”– Indicates that the proportion of elderly is

increasing• Negative implications for business and

industry

ItalyNote the large population of ages 30-49

ItalyNote how the larger numbers of persons are moving into older age groups and the number of children is decreasing

Population Projections for the U.S.Projections shift drastically with changes in fertility. Contrast the 1988 projection based on a fertility rate of 1.8, with 2000 projection based on an increased fertility rate of 2.0 and current immigration

Population Projections for Developing Countries

• Fertility rates are dropping, but they are still well above replacement level

• Average TFR (excluding China – 1.6) is 3.4

Iraq’s population in 2005TFR = 4.8. Assuming that this fertility rate will gradually decline to 2.7 in 2025,t he population will increase from 29 to 40 million

Iraq Population 2025

“Ideal” Population Structure

• Equal numbers of persons in each age group, and a life expectancy of 75 years

Population Momentum

• Refers to the effect of current age structures on future populations– Iraq – positive population momentum• Small portion of the population is in the upper age

groups and many children are entering their reproductive years

– Europe – negative population momentum• Consequence of low fertility rate • Prompted several countries (e.g. France) to adopt a

pro-natal policy

Comparing Projected Populations

Demographic Transition

• Basic premise is that there is a link between modernization and a decline in birth and death rates

Birth Rates/Death Rate

• Crude Birth Rate (CBR)– Number of Births per 1,000 of the population per year

• Crude Death Rate (CDR)– Number of Deaths per 1,000 of the population per year

• Subtracting the DCR from the CBR gives you the increase (or decrease) per thousand per year– Dividing this number by 10 gives you the percent

increase or decrease of the population

Growth Rate

b/1000 – d/1000 = natural rate of increase

Natural rate of increase / 10 = % increase

A zero growth population is achieved if, the CBR and CDR are equal

Doubling Time

• Number of years it will take a population growing at a constant percentage per year to double

• Calculated by dividing the growth rate into 70

Epidemiologic Transition• Reminder: Epidemiology is the study of factors affecting the health and

illness of populations

• Throughout most of human history, crude death rates were high– 40+/1000

• By middle of the 19th century, epidemics and other social conditions were responsible for high death rates began to recede

Epidemiologic Transition

• Developing countries CDR is at about 10/1000• Cancer, cardiovascular disease, and other

degenerative diseases account for the majority of the mortality

• Pattern of change in mortality factors is referred to as the epidemiologic transition

Fertility Transition

• Now developed countries, birthrates have declined from 40 – 50 /1000 to 9-12/1000.

Phase I

• Demographic transition – Primitive stability– Results from both death rates and birth rates

being high– Small population size

Phase II

• Demographic Transition– Declining in CDR (epidemiological transition)– CBR still stays high– Population growth accelerates

Phase III

• Demographic Transition– Declining CBR – (fertility transition)– Population growth still remains high, but begins to

slow down

Phase IV

• Demographic Transition– CBR = CDR, or CBR < CDR