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Population. Population Ecology Is concerned with changes in population size and the factors that regulate populations over time. European starling. 0. The Spread of Shakespeare’s Starlings The European Starling Has become an abundant and destructive pest in North America. 4.0. 3.8. 3.6.

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Population Ecology

Is concerned with changes in population size and the factors that regulate populations over time




  • The Spread of Shakespeare’s Starlings
    • The European Starling
      • Has become an abundant and destructive pest in North America




Clutch size














Density of females

Figure 36.5A


Multiple factors may limit population growth

  • As a population’s density increases
    • Factors such as limited food supply and increased disease or predation may increase the death rate, decrease the birth rate, or both






Human population size (billions)

The Plague


















Figure 36.9A


The human population has been growing almost exponentially for centuries, standing now at about 7 billion

baby boom
Baby Boom
  • The baby boom was in the 1950s when the American birthrate skyrocketed.
  • When the so-called baby boomers were in their 20s, they were young and vibrant, and they added to American productivity.
  • Today, however, the boomers are aging. Their children worry that elderly boomers will drain resources, not to mention national attention, from younger adults.
human population growth
Human Population Growth
  • The world population increases the equivalent of a medium-sized city (200,000) every day and the equivalent of a country the size of Germany (80 million) every year.
  • Most of the growth is coming from less-developed countries.
human population growth1
Human Population Growth
  • Right now, there are about 7 billion people on the planet, but in the next 100 years, there will be about 11 billion.
  • All populations need nutrients, space, water, and energy.
human population growth2
Human Population Growth
  • This means that in about 50 years, the world will need double the amount of food, jobs, water, energy, and so on to maintain the same standard of living.
  • Right now, half of our world’s population do not have electricity or indoor water and cannot read even enough to sign their name.
human population growth3
Human Population Growth
  • We are adding a billion more people to the planet much faster than we used to.
  • We got our first billion in 1800; the second billion arrived in 1930; the third billion in 1960; and today there are 7 billion.
  • Only if the growth rate continues to decline can there be zero population growth when births equal deathsand the population size remains steady.
the more developed versus less developed countries
The More-Developed Versus Less-Developed Countries
  • The MDCs of North America, Canada, England, and Europe, have a population growth under control and the people enjoy a good standard of living.
  • The LDCs of South America (Argentina, Brazil, Chile), Africa, and Asia, have population growth out of control and the majority of people live in poverty.
the more developed versus less developed countries1
The More-Developed Versus Less-Developed Countries
  • The term “third-world countries”is an old term used to mean the less-developed countries.
  • This term was introduced by those who thought of the United States and Europe as the first world and the former USSR as the second world.
the more developed versus less developed countries2
The More-Developed Versus Less-Developed Countries
  • The MDCs doubled their populations between 1850 and 1950 because of a decline in the death rate and modern medicines.
  • The populations of a few of the MDCs, Italy, Denmark, Hungary, Sweden are actually decreasing in size.
  • In contrast, there is no leveling off and no end in sight to U.S. population growth.
  • Although the death rate began to decline steeply in the LDCs following World War II with the importation of modern medicine from the MDCs, the birthrate remained high.
comparing age structure
Comparing Age Structure
  • One way of characterizing population is by age groups.
  • If there are more young women entering the reproductive years than there are older women leaving them, there will still be an increase in population.
  • Most LDCs have a large proportion of young women under the age of 15.
possible solutions
Possible Solutions

1. Establish and/or strengthen family

planning programs.

2. Use social progress to reduce the

desire for large families by providing

education, raising the status of

women, and reducing child mortality rate.

3. Delay the onset of childbearing by

five years and wider spacing of births.

the human population and pollution
The Human Population and Pollution
  • Intact ecosystems naturally prevent soil erosion, dispose of environmental wastes, provide fresh water, regulate climate.
  • But as the human population increases in size, more ecosystems are impacted by humans.
  • Ecosystems are no longer able to process and rid the biosphere of wastes and leads to problems for all living things, and also problems in the air, in the water, and on land.
the human population and pollution1
The Human Population and Pollution
  • Air pollutants in particular are involved in causing major environmental effects, including global warming, acid rain, and ozone depletion.
fossil fuels
  • Problems with the use of fossil fuels such as coal and oil and gas include the fact that they are nonrenewable, they pollute the environment when they are burned, oil and gas wells pollute the environment by emitting greenhouse gases, and they are contributing to the problem of global warming.
  • The trend for the future is the use of hydrogen for energy.
  • Hydrogen-based fuel cells are in use now in some cities to power vehicles, can be produced locally all over the world, and will reduce global warming and air pollution.
  • Pollution is any undesirable change in the environment that can be harmful to humans and other life, and does not normally occur.
  • Natural ecosystems are stable in the sense that they take care of themselves and are balanced in the interaction of the species in them.
  • There is just enough food and energy to support the populations in them.
  • Human-impacted ecosystems essentially have two added parts: the country, where agriculture and animal husbandry are found, and the city, where most people live and where industry is carried on.
  • These two systems require two major inputs: fuel energy and raw materials (e.g., metals, wood, synthetic materials).
  • The use of these necessarily results in waste and pollution.
cuyahoga river
Cuyahoga River

A river in northeast Ohio, USA, into which industries around Cleveland dumped oily wastes, and which has literally caught fire on numerous occasions.

The most serious fire occurred on 23 June 1969, and that event triggered a series of important pollution control initiatives including the Clean Water Act (1972) and the Great Lakes water quality agreement, and the creation of federal and state environmental protection agencies.

the country
The Country
  • The country areas are where our food is grown, but it has an impact on our ecosystem.

1. Heavy use of fertilizers and pesticides contribute to water pollution, and pesticides kill off beneficial soil organisms.

2. Generous irrigation by river water will dump a heavy concentration of salt back into the river. The salt content of the Rio Grande River in the Southwest is so high that the government has built a treatment plant to remove the salt.

3. Excessive fuel consumption for water pumps and large farming machines.

4. Loss of land quality. Evaporation of excess water can leave behind excess salt, making it unsuitable for the growth of more crops.

the city
The City
  • Industries increase the amount of carbon dioxide in the atmosphere.
  • The city is dependent on the country to meet its needs. For example, each person in the city requires several acres of land from the country for food production.
  • As the population increases, the amount of farmland goes down when it needs to go up.
  • Cities currently rely mainly on coal and oil for fuel.
the city1
The City
  • The city wastes fuel in many ways.
  • An office building with lights always on and windows that cannot be opened.
  • People who drive cars long dis­tances instead of carpooling or taking public transportation and who drive short distances instead of walking or bicy­cling.
  • Materials are not always recycled.
  • Note that having an air conditioner on during a hot day is NOT an example of wasting fuel.
  • Burning fossil fuels causes air and water pollution.
  • Chemical and solid wastes cause pollution, both during its production and when it is discarded.
  • Humans themselves produce much sewage that is discharged into bodies of water, often after only minimal treatment.
the solution
The Solution
  • In human-impacted ecosystems, fuel combustion by­products, sewage, fertilizers, pesticides, and solid wastes all are added to the environment in the hope that natural cycles will cleanse the ecosystem of these pollutants.
  • However, we have exploited natural ecosystems to the extent that the environment is overloaded.
  • We have an ever-increasing number of people want to maintain a standard of living that requires many goods and services.
  • But we can help this if we achieve zero population growth and if we conserve energy and raw materials.
conservation can be achieved
Conservation Can Be Achieved
  • Wise use of only what is actually needed
  • Recycling of iron, copper, lead, and aluminum
  • Use renewable energy resources
  • Development of more efficient ways to utilize all forms of energy
working with nature
Working With Nature
  • Some farmers have adopted organic farming methods and do not use fertilizers or pesticides.
  • Instead, they use special planting techniques to control weeds, crop rotation to combat major pests, and the growth of legumes (a type of bean that makes nitrogen) to supply nitrogen fertility to the soil.
working with nature1
Working With Nature
  • Some farmers use natural predators and parasites instead of pesticides to control insects.
  • Organic farms require only about two-fifths as much fossil energy.
  • There is one-third less soil erosion.
  • It is important to consider that ecosystems should be developed and managed with care so that their integral nature is preserved.
  • This is often called “working with nature” rather than against nature.
pollution of oceans
Pollution of Oceans
  • Pesticides and other chemicals get into the ground and water supply, and new plants absorb them, animals eat the plants, and humans eat the plants and the animals.
  • In that way, our bodies pick up these toxins.
pollution of oceans1
Pollution of Oceans
  • The oceans are the final receptors for water pollutantscarried by rivers.
  • Waste products that are dumped into areas that drain into the ocean can also be washed back to shores.
  • The plastic piece that holds a six-pack of cans gets tangled in birds, fishes, and marine mammals, causing their death.
pollution of oceans2
Pollution of Oceans
  • Oil spills in the ocean kill plankton, fish, and shellfish, as well as birds and marine mammals.
  • The largest tanker spill in U.S. territorial waters occurred on March 24, 1989, when the tanker Exxon Valdez struck a reef in Alaska and leaked 44 million liters of crude oil.

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