Ecology Population Teacher Notes

Vocabulary words/Important People or Groups: Population, Population density, Population dispersion, Exponential growth, Carrying capacity, Density-dependent factors, Density-independent factors, Hunter-Gatherer Societies, Agricultural Societies, Industrial Societies, Thomas Malthus, Agricultural Revolution, Industrial Revolution, Germ theory, Ellen Richards, Food and Agriculture Organization, Demography, Age structure, Survivorship, Fertility rate, Migration, Immigration, Emigration, Growth rate, Birth rate, Death rate, Demography transition, Life expectancy, Infant mortality, Arable land, Urbanization

Population- set of the same species of organisms living in the same location at the same time.

Properties of Populations

  • Population density-the number of the same species of organisms living in the same area
  • Population dispersion-describes how the population of the same species lives per area. For instance wide spread in one area but random in other areas of the world.
  • When populations are growing, they exhibit an exponential growth
  • As the population gets larger, it grows at a faster rate
  • This population growth cannot continue indefinitely
  • The population growth stabilizes: deaths will begin to exceed births
  • Population numbers will fall to a level that the environment can support-Carrying capacity

  • In graphs the S-shaped curve represents the change in the size of a new population

Some organisms (such as mosquitoes) undergo rapid population growth, which declines when conditions become unfavorable

Some organisms (such as elephants) have long lives and tend to maintain population sizes at carrying capacity

Limiting factorsslow growth: food availability, predators, lack of space, disease

Two types:

  1. Density-dependent factors are limiting factors that have a greater effect as the population increases and are related to competition and other interactions between organisms
  2. Include disease, competition, predators, parasites, food, and water
  3. Density-independent factors are limiting factors that affect populations size regardless of the density
  4. Include storms, floods, drought, habitat disruption, fire, and climate

Human Population

History of Human populations

According to fossil records the first humans were found in South Africa more than 200,000 years ago. Homo sapiens (Humans) appeared in Southeast Asia about 100,000 years ago and everywhere else roughly 40,000- 60,000 years ago.

  • During an Ice Age roughly 60,000 years those in Russia and nearby areas crossed into Alaska since the ocean was frozen.

The Nile River is the second largest river in the world. Because of the fertile land and the abundant water supply the Nile River valley area of Africa continuously has had a settlement there for over 5,000 years.

  1. Human Societies
  2. Hunter-Gatherer Societies
  3. Is a society in which people gather natural food, hunt, and are nomadic
  4. Do not plant crops
  5. Do not attempt to control natural resources, live within the ability of the land to sustain it
  6. Population density is low
  7. Small impact upon environment
  8. Agricultural Societies
  9. Began when people started to plant crops and raise animals for food (roughly 10,000 years ago)
  10. People stopped roaming
  11. Work began to be divided among members of society
  12. Invention of plow enabled people to plant more land and grow more food
  13. Human population began to grow
  14. Fewer people had to farm
  15. Formed cities and began crafts and manufacturing goods
  16. Trade networks developed to move food into city and move goods out of the city
  17. Agricultural society is one in which crops are grown and people have specialized roles
  18. Can sustain itself indefinitely if it lives within the limits of its environment
  19. Early societies harmed land, leading to desertification
  20. Logging, grazing, poor farming practices destroyed soil and vegetation
  21. Loss of vegetation changed patterns of rainfall
  1. Industrial Societies
  2. Began in late 1700’s when machinery was invented that allowed more food to be produced by fewer people
  3. Demanded large amounts of energy and resources
  4. Advances began to be accomplished in other areas
  5. Plants were bred to increase crop yield
  6. Genetic research
  7. Advancements were made in medicine
  8. Population began to grow quickly
  9. Has led to environmental damage
  10. Pollution
  11. Technology can be used to solve problems

Additional History that affected Human populations

Thomas Malthus (1798) noted that the human population was growing exponentially (1, 2, 4, 8, 16 etc.), while food supply was increasing arithmetically (1, 2, 3, 4 etc.)

  • Predicted that the world was nearing carrying capacity for humans
  • Populations was around 1 billion; is now about 7.1 billion

Agricultural Revolution-Occurred when the shift from harvesting wild food sources to producing food through the techniques of farming and herding

  • In the past 300 years population has grown because of the Industrial Revolution
  • Technological advancements lead to increased food production, better distribution of products, safer working conditions, reduction of hours in the work day, better medical care, and better housing conditions
  • The germ theoryhelped physicians realize that diseases are caused by bacteria and other microorganisms
  • Led to improved hygiene methods, better waste disposal, and water treatment

In 1873: Ellen Richards became the first woman to graduate from the Massachusetts Institute of Technology-Chemistry. Her research led to the development of water quality standards in the USA. Her work helped reduce the threat of diseases such as cholera, typhoid fever, and dysentery.

  • Discovery of antibiotics and vaccines
  • Death rate decreased especially in infants and children

Food and Agriculture Organization (FAO) of the United Nations estimates the biological carrying capacity of Earth to be about 50 billion people

  • Every resource would have to be devoted to maintaining human life with no energy for luxuries (cars, A/C, etc.)
  • Would result in more regulation of personal freedoms as populations become more crowded
  • Cultural carrying capacity is the level at which the maximum human population can be maintained at an acceptable standard of living
  • Would vary among nations as there are differences in social expectations and values
  • Would change as technology improves agriculture, lessens effects of pollution, & develops new energy sources

Declines in Growth Rate

  1. Disease
  1. Bubonic plague (Black Death)-occurred in Central Europe and Asia in the 1300’s killing over 25% of adult populations and in England over 50% -caused by rats
  2. Yellow fever, malaria, cholera, typhus, and smallpox have all claimed hundreds of 1000’s lives.
  1. Famine
  1. Irish Potato Famine of the 1840’s –over a million deaths due to potato crops being destroyed due to a disease called potato blight (was the main food staple in Ireland)
  2. China during 1876-1879 famine killed over 9 million people
  1. Wars
  2. The Great Depression (1929-1939)

Growth & Changing Needs

  1. Overpopulation is seen as a major environmental problem
  2. More developed countries (Australia, Canada, Germany, Italy, Japan, USA, & England) are industrialized nations
  • Have relatively high personal incomes
  • Populations are stabilizing
  • Prosperous families are more likely to expect to feed, clothe, & educate their children & consequently have fewer of them
  • In USA, population is increasing at about 1.1% per year
  • About 1/3 of these are immigrants
  • Dams have been built to allow more people to live closer to the water and block floodwaters.
  • Problem with dams is that the once fertile areas from flooding (due to slit deposits-full of minerals necessary for crops) is not be replenished
  • Causing farms to fail (USA, Nile River Valley of Africa, and Egypt)
  1. Less developed countries (such as Botswana, Bolivia, Chile, Ethiopia, India, Kenya, & Rwanda) have varying levels of industrialization
  • Have low personal incomes
  • Population growth is slow to fast
  • Example: Kenya is doubling its population every 30 years
  • Governments, farmers, religious, economists may see this as an asset
  1. Demographics

Demographics

Demography – The science of the changing of vital statistics of the human population regarding age, wealth, education, etc.

  • Are useful in predicting future populations
  • Fewer young people than old people indicates the population may shrink in the future
  • More young people indicate future growth
  • Stabilization occurs when the number of children surviving to reproductive age equals the number of parents in the preceding generation
  • Age structure-The distribution of ages in a specific population of organisms in a specific time frame
  • Survivorship-the percentage of a population that will live to a certain age
  • Fertility rate-The average number of births a woman has in her lifetime
  • Migration-The moving of a person from one location to another
  • Immigration-The number of people moving in to another area they were not born in
  • Emigration-The number of people moving out of an area
  • Growth Rate: Birth rate – death rate
  • If the birth rate equals the death rate, then the growth rate is zero
  • Birth rate-Number of births per 1,000 individuals in a population
  • Death rate-Number of deaths per 1,000 individuals in a population
  • Growth rates can be positive or negative
  • Demographic transition-explains how social and economicchanges affect population growth rates

Life expectancy- The average amount of time a male or female lives

  • Often depends on where they live
  • Also affected by infant mortality (the death rate of babies under one year old) of a country
  • The ratio between males and females is 125 males to 100 females
  • The actual ratio because of infant mortality is 105 males to 100 females

A larger portion of males are stillborn or die from miscarriages

Males in general usually have lower life expectancy than females too

Problems of Overpopulation

  • Impacts the land
  • Building dams-less farm land available (arable land)
  • Urbanization-Moving from rural areas to the cities
  • Big problem in the USA and China
  • Pollution, disease overuse of resources, environmental damage are all issues
  • Forcing people to limit family size is generally considered unethical
  • China undertook this in the 1980s
  • Only married couples could have children
  • Young people were encouraged to wait for marriage by extra food, money, better housing, free contraceptives, abortion, and sterilization
  • Abortion was coerced among unmarried women and those have a third child

Those with second children were socially ostracized

  • Education and providing birth control seems to be the answer
  • Less –Developed Nations: Have much higher growth rates (accounts for 96 % of world population)
  • More-developed countries that are seeing high growth rates are due to immigration from less-developed countries
  • Social and religious issues must be considered
  • Some countries such as Bulgaria, Hungary, Latvia have death rates that exceed birth rates
  • Threatens military and government
  • Some researchers believe that technology will solve problems and population rates will stabilize by 2050.

1