Ch35: Population ChangeCh35: Population Change

Higher Human BiologyHigher Human Biology

PopulationPopulationA population is a group of individuals of the same species which makes up part of the community in an ecosystem.

When a population colonises a new environment the population increases rapidly until it reaches the carrying capacity - the maximum population size that can be maintained by the environmental conditions.

Populations terminologyPopulations terminologyPopulation density – the number of individuals of the same type present per unit area (or volume) of a habitat.Birth rate – the number of new individuals produced by a population during a certain time interval.

Death rate – the number of individuals within a population that have died during the same time interval.

Population Growth CurvePopulation Growth Curve

Time

Number of Individuals

Carrying capacity

Exponential growth

Rapid increase in population size

Birth = Death rate ratePopulation

colonising a new

environment

Population StabilityPopulation StabilityWhen the population reaches the level that the available environmental recourses can just maintain the population becomes stable. At this stage it is in a state of dynamic equilibrium (there are very slight changes but overall it is relatively balanced) and the population has reached its carrying capacity and birth rate equals death rate.Human interference has caused many populations to become unstable or threatened.

The carrying capacity is determined by: Population RegulationPopulation Regulation

• Food• Oxygen• Water• Space

If one is limited it prevents the population increasing

Regulatory Effect

• Predation• Disease• Pollution by organism’s waste

Population decrease

Death by….

Regulation of population sizeRegulation of population size

Population at Carrying capacity

(maximum supported by the environment)

factor limited e.g. food, water

Population

decrease

Population

increase

Population decrease

Death rate increases

Factor plentiful e.g. food, water

Population increase Birth rate increases

Agricultural

Humans have overcome causes of mortality (e.g. predation) so have increased our carrying capacity & have increased exponential growth.

Human Population ExplosionHuman Population Explosion

Revolutionary changes

Rapid population increase

Industrial

• Totally dependent on immediate environment for food, water, shelter.• Live ‘hand to mouth’• No agriculture• No modern technology

Undeveloped SocietiesUndeveloped Societies

Kalahari Bushmen(Africa)

Aborigines(Australia)

e.g. Hunter-gatherers• remote locations• low carrying capacity• low population density• shared society

Arctic Inuit (Eskimos) Population limited by water

availabilityPopulation limited by

low temperature

Influence of modern society on Influence of modern society on undeveloped societiesundeveloped societies

Modern societies have introduced: • tools• technology• disease – led to a population declineCaused problems:• Less land to live off• Traditional cultures are disappearing• Economic & social problems

• Grow crops on own land to meet the families own needs. • Store excess crop for use during times of shortage• Rarely sell any crops or animals• Use basic tools• Use family labour

Subsistence farmingSubsistence farming

Common in Latin

America, Africa &

Asia

• Low standard of living • Often no electricity or sanitation

• Lifestyle similar to 10,000 y.a. at start of agricultural revolution• Population denser than hunter-gatherers

Subsistence Subsistence farming (cont’d)farming (cont’d)

Piped water

Immunisation against diseases e.g. smallpox &

polio

Better housin

g

Effect of Science on Human Effect of Science on Human Population GrowthPopulation Growth

Antibiotics

Modern sanitation

Improvements in child

careEfficient food production

Effect of Science on Human Effect of Science on Human Population GrowthPopulation Growth

1650 AD Advances in

science

Scientific discoverie

s & Inventions

Industrial revolution

Advances in

medicine

These advances have contributed to a human population boom by removing limiting factors that in the past regulated the

population.

Exponential Growth Exponential Growth of Human Populationof Human Population

The human population is now growing exponentially due to:

Overcoming predation (due to guns)

Less child mortality

Increase in life expectancy

Increased female fertility

Fertilisers

Exponential GrowthExponential GrowthAlso due to…

Increased food availabilityMachinery

Pesticides

Change in Cultural HabitsChange in Cultural HabitsWomen tend to suckle their young for less time, as ovulation is inhibited during breast-feeding, women are more likely to conceive their next child sooner.

Births no longer spaced

outBirth rate increases

Doubling Doubling timetime… the length of time for the worlds

population to double.

In 1980s doubling time

was decreasing

steadily thus the world

population was rapidly

increasing

Actually the population growth rate is slowing

down due to…

• use of contraception• social pressures (e.g. China)• deaths from AIDS

World’s wealth is not distributed evenly

The highest population growth is in the poorest

nations so 50% of the world population live in poverty!