Population Ecology Part II HUMAN POPULATION DYNAMICS.

Population Ecology Part IIHUMAN POPULATION DYNAMICS

Thomas Malthus “diminishing returns”He argues that rising wages and improved well-being would lead to excess reproduction among the working class.A labor surplus would then cause wages to fall below subsistence levels, resulting in starvation, disease and crime. In his view, land for food production was the limiting factor in both population growth and economic development.

Was Malthus Right?

The Black Plague

Also called the “black death” or Bubonic plagueDeadliest pandemic in human history1340’s and 1350’sThought to have been a bacterial infection carried by fleasDensity dependent

Bubonic Plague

30%-75% mortality rateBulbous swelling in lymph nodesTurned black

Pneumatic PlagueCaused a form of pneumoniaSame bacterium90%-95% mortalityVictims died before reaching other places

Septicemic Plague100% mortalityHigh feverSkin turned purple

The Catholic ChurchLost prestige and spiritual authorityPromised cures and treatmentsSaid it was God’s willCould not explain so many deathsPeople abandoned the church

Effect on Europehttp://www.insecta-inspecta.com/fleas/bdeath/Europe.html

Why has the human population been able to

continue exponential growth when other

populations would have leveled off by now?

Humans Have Been Able To Overcome

Environmental Resistance (Limiting Factors) to

Sustain Growth

Arable LandLand that can be used for growing crops21% of earth’s surface is arable

Reasons for World Hunger Issues

Unequal distribution of available foodLoss of arable landIncreasing population growth rateIncreasing poverty in developing countries

Arable LandAssume no arable land is being lost for the next 33 years.2006, there was 1.15 acres of arable land per person, world-wide(i.e. 7.68 billion acres / 6.68 billion people).

Arable Land2039, there may be only 0.59 acres of arable land per person, world-wide i.e. 7.68 billion acres / 13 billion peoplearable land is being lost at the alarming rate of over24.7 million acres per year.   2039, there may be only 0.53 acres of arable land per person, world-wide

Reasons for Loss of Arable LandDeforestationOver exploitation for fuel woodOvergrazingOver farming (deplete nutrients)IndustrializationNo rich sediment replacement due to flooding – controlled by dams

How have we still managed to grow enough food to feed the world?Who grows most of the food?What affect could global warming have on this scenario?

Ways to Increase Crop Production

Modern farm equipmentReturn nutrients to soil (fertilizers)IrrigationNew genetically modified cropsHydroponics

Strategies for ensuring adequate nutrition for a growing population:

Increase the number of new food crops from a diversity of plant speciesDistribute food more equitablyIncrease land are that is dedicated to grain production rather than meat productionAssist developing countries in efficient crop irrigation systems.

How many people can the earth feed on our

arable land?What about over-fishing

our oceans?What is the earth’s carrying capacity?

Factors Affecting Human Population Size

#1 – Birth vs. Death RatesBirth rate - # live births per 1,000 peopleDeath rate - # of deaths per 1,000 peopleTop 5 most populated countries: China, India, U.S., Indonesia, Brazil

Annual Rate of Natural Population Change (%)=

Birth rate – Death rate 1,000 people x

100

#2 - Fertility Rate# children born to a woman in her lifetime

Replacement-level fertility rate = # children a couple must have to replace themselves (2.1 to 2.5)Total fertility rate = average # children a woman has during reproductive years (global average is 2.7, developed countries 1.6)

#3 – Factors Related to Children

Importance of children to labor forceCost of raising and educating a child ($250,000 in U.S. to age 18 vs. minimal in developing countries)

#4 – Religion and CultureView of the familyRights of womenBeliefs concerning birth controlAge at marriageSex preference for children

#5 - Pension SystemIf retirement plans are available and adequate – less childrenNo retirement – more children, particularly males to support them in old age

#6 - UrbanizationBetter access to family planning servicesMore job opportunitiesHigher standard of livingAll generally promote smaller families

#7 – Opportunities for WomenEducationFamily Planning optionsJob opportunitiesBest way to reduce fertility rates

#8 – Infant Mortality RateBetter medicine and health care = lower infant mortalityThe more likely infants are to survive, the more fertility rates drop

#9 – Average Age at Marriage

Developing countries = 14 or 15Developed countries = 25

#10 – Life ExpectancyRapid rise in world population in last 100 years is due to increased life expectancyModern medicine means infants do not die and people live to much older ages67 years globally, 78 years in U.S.Poorest countries with HIV = 49 years

What factors affect death rates?1.Increased food supplies and

distribution

2.Better nutrition

3.Improvements in medical & public health technology (ex. immunizations and antibiotics)

4.Improvements in sanitation & personal hygiene

5.Safer water supplies to stop spread of infectious disease

#11– Net MigrationImmigration vs. EmigrationCountries like the U.S. continue to grow due to ImmigrationCountries like Russia are decreasing due to emigration

#12 – Age Structure

Growth Rate- includes birth rate, death rate, immigration and emigration

Gross National Product- The most commonly used measure of the economic growth of a country.

Population ChangeGrowth Rate

Population change = (Crude birth rate + Immigration) – (Crude death rate + Emigration)If a population of 10,000 experiences 100 births, 40 deaths, 10 immigrants and 30 emigrants in a year, what is the net annual percentage growth rate?

Answer(100 + 10) – (40 + 30) = 4040/10,000 X 100 = 0.4%

Zero Population Growth- When the number of births, equals the number of deaths. No growth in the population.

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Rule of 70’s – Doubling TimeDoubling time - # years it takes a population to double70/ growth rate = doubling time (daily)72/ growth rate = doubling time (years)If a population of a country grows at a rate of 5% a year, the number of years required for the pop to double is what?

Demographics of Countries

Developing Countries-China is the largest but has taken drastic population control methods. By 2050, India is predicted to pass it. Pakistan is projected to become 3rd with Iran and Ethiopia following. However, Russia is losing 600,000 people a year, after being the 4th largest country in 1950. This is because of environmental pollution, hyperinflation, crime, corruption, disease and despair.

Developed countries

Usually don’t have such population problems. It can be linked to poverty level even in developed countries.

Demographic Transition

As countries becomes industrialized their birth rates decline.

Pre-industrialHarsh living conditions lead to a high birth rate and high death rate. Thus, there is little population growth.

TransitionalAs industrialization begins, food production rises and health care improves.Death rates drop and birth rates remain highThe population grows rapidly

IndustrialIndustrialization is wide spreadBirth rate drops and eventually approaches the death rate.This is because of:

better access to birth control decline in the infant mortality rate increased job opportunities for women the high cost of raising children who don’t enter the work force until after high school or college.

Reasons human population growth has been so dramatic in the last century

The Industrial RevolutionModern Medicine

PostindustrialThe birth rate declines even further, equaling the death rate and thus reaching zero population growth.Then, the birth rate falls below the death rate and the total population size slowly decreases.

(Cont….)

37 countries have reached this stage. (mainly in W. Europe)

To most population experts, the challenge is to help the remaining 88% of the world to get to this stage.

Demographic Transition

Demographic Transition in Japan

U.S. StatisticsBecause of the ‘Baby Boom’ the US has a bulge in the pyramid with people in their 50’s-60’s.There are also more women than men in the older age group because of differences in longevity between the sexes.

(Cont…)

The US has a high % of retired people because of long life expectancy. This makes us realize the importance of social security, etc.

The US is considered a slow growth population.

Some countries, including China, penalize couples who have more than one or two children by:

1. Raising their taxes

2. Charging other fees

3. Eliminating income tax deductions for a couple’s third child

4. Loss of health-care benefits, food allotments and job options

In China couples who pledge to have no more than one child receive

1. Extra food

2. Larger pensions

3. Better housing

4. Free medical care

5. Salary bonuses

6. Free school tuition for their one child

7. Preferential treatment in employment when their child enters the job market.

However, according to some studies, there is a strong preference for male children.

1.Girls are aborted at a higher rate than boys

2.Some infant girls are killed

3.Male children sometimes are fed better than female children.

Environmental Impact Equation (Paul Ehrlich Formula)

Population X affluence X technology = Environmental impact

Developed CountriesHigh rates of resource use Result in high levels of pollution and environmental degradation per person These are believed to be the key factors determining overall environmental impact.

(Cont….)

It is estimated that a US citizen consumes 35 X’s as much as the average citizen of India and 100 X’s as much as the average person in the world’s poorest countries.(Cont…)

Thus, poor parents in a developing country would need 70-200 kids to have the same lifetime environmental impact as 2 typical US kids.

Urban areas must import food, water, energy, minerals, & other resources.

They produce enormous quantities of wastes that can pollute the air, water & land.

44% of the world’s people live in urban areas that occupy only 5% of the world’s land & they consume 75% of the world’s resources.

Urbanization

1994 Global Summit on Population & DevelopmentCairo, EgyptEncouraged action to stabilized the world’s population at 7.8 billion by 2050, instead of the projected 11-12.5 billion.

The major goals are to:Provide universal access to family-planning services.Improve the health care of infants, children & pregnant womenEncourage development of national population policiesImproving the status of women by expanding education & job opportunities

Major goals continued:

Increase access to education for girlsIncrease men’s involvement in child-rearing responsibility & family planningTake steps to eradicate povertyReduce & eliminate unsustainable patterns of production & consumption.