Environmental Science Ch' 13: Population Growth

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Environmental Science Ch. 13Population Growth
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Ch. 13-1 How Populations Change In Size

• Key Terms
• Biotic Potential
• Carrying Capacity
• Limiting Resource

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California Content Standards for Science
Addressed

• Life Science
• 6(b) Students know how to analyze changes in an
  ecosystem resulting from changes in climate,
  human activity, introduction of nonnative
  species, or changes in population size.
• 6(c) Students know how fluctuations in population
  size in an ecosystem are determined by the
  relative rates of birth, immigration, emigration,
  and death.

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Ch. 13-1Why Do I Need To Know This?

• Because we need to understand how all populations
  grow in order to understand what will happen if
  the human population continues to grow.
• Because there are things that limit the growth of
  the human population and if we are not careful,
  will limit the growth of the human population.
• Because humans may already be at their carrying
  capacity for the entire planet!

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Key Sections Ch. 13-1

• How Populations Change In Size
• How Fast Can Populations Grow?
• What Limits Population Growth?

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How Populations Change In Size

• Presently, there are over 6 billion people living
  on the planet.
• It is estimated that by the middle of the 21st
  century, the human population will exceed 9
  billion!
• We cannot sustain this level of population growth
  on the planet for much longer!

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How Populations Change In Size
The Formula that Shows Population Growth
Is Number of Births Number of
Deaths gt Number of Immigrants Number of
Emigrants The Formula that Shows Population
Decrease Is Number of Deaths Number of
Births gt Number of Emigrants Number of
Immigrants
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How Fast Can A Population Grow?

• How fast a species can reproduce is called its
  biotic potential.
• Most species have more offspring than can survive
  into adulthood.
• The biotic potential for each species is the rate
  of growth of the species if each child survived
  to adulthood and reproduced at its maximum
  capacity.
• This is called exponential growth because the
  graph of the line curves up like a J.
• The biotic potential for humans is about 6 per
  year.
• Rats have a biotic potential of 1.5 per day!
• Flies have a biotic potential of over 1000 per
  day!

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How Fast Can A Population Grow?

• Biologist have identified 2 survival strategies
  for a species.
• One is called a J strategy and is best typified
  by the salmon.
• Salmon lay thousands of eggs at one time and then
  die. Therefore the do not help their offspring
  at all (and may even eat them!).
• The other is called a k strategy and is best
  typified by humans.
• Humans tend to only have 1 child at a time and
  invest a lot of time raising them.
• Both strategies lead to the survival of enough
  members of the species to continue it.

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What Limits Population Growth?

• If there were no limits on population growth, the
  planet would have been overrun.
• In every ecosystem there are limiting factors
  that prevent the growth of a population.
• For animals, the limiting resources are often
  food, water, and shelter.
• For plants, the limiting resources are sunlight,
  water, and nutrients.

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What Limits Population Growth?

• As populations grow, the competition for the
  limited resource increases.
• This leads to a rise in diseases, predators,
  parasites, etc. and slows the growth of the
  population.
• The combined effect of all these limiting
  resources is called environmental resistance.
• Eventually, the population stabilizes near its
  carrying capacity (although the population always
  fluctuates slightly above or slightly below the
  carrying capacity).
• Any change to the environment can change the
  carrying capacity for the species.

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Ch. 13-2 A Growing Human Population

• Key Terms
• Agricultural Revolution
• Hunter-Gatherers

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California Content Standards for Science
Addressed

• Life Science
• 6(b) Students know how to analyze changes in an
  ecosystem resulting from changes in climate,
  human activity, introduction of nonnative
  species, or changes in population size.
• 6(c) Students know how fluctuations in population
  size in an ecosystem are determined by the
  relative rates of birth, immigration, emigration,
  and death.

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Ch. 13-2Why Do I Need To Know This?

• Because the human population is growing at an
  alarming rate which is causing global problems!
• Because at some point the human population will
  exceed the number of people who can live on the
  planet (if we havent already reached it), and
  that could lead to major global problems.
• Because overpopulation affects everything from
  immigration to economies to wars.
• Because we can help control the growth of the
  human population, especially in the developing
  countries, by understanding what happens to
  populations as they become more developed.

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Key Sections Ch. 13-2

• A Growing Human Population
• From Hunting and Gathering To Agriculture
• The Population Continues To Grow
• The Demographic Transition
• A Demographically Divided World

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A Growing Human Population

• Like a single ecosystem, the entire Earth has a
  carrying capacity.
• Scientists are not sure what the planets
  carrying capacity is for humans to be somewhere
  between 4 billion and 16 billion people.
• The reason why it is so difficult to estimate the
  carrying capacity for humans is that with
  technology we can alter our carrying capacity.

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From Hunting and Gathering to Agriculture

• For about 99 of human history, humans were
  hunter-gatherers.
• Hunter-gathers lived in small bands (about 25-50
  people) and traveled from place to place to hunt,
  fish, and get food.
• About 10,000 years ago, around the world, people
  began to raise crops and farm animals, leading to
  a change called the agricultural revolution.
• This lead to much more food availability and the
  world-wide population began to rise.

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The Population Continues To Grow

• By about 1800, the worlds population reached
  about 1 billion people.
• Between 1800 and 1930, the worlds population
  doubled to 2 billion people!
• By 1975, the worlds population doubled again to
  4 billion people!
• The rapid rise in population had to do with
  improvements in medicine, technology and access
  to freshwater which all greatly increased the
  average persons life span.
• During the hunter-gatherer phase, the average
  person lived to be about 30.
• By 1990, the average person lived to be about 70.

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The Population Continues To Grow
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The Demographic Transition

• At the present, the worldwide population is still
  growing rapidly, although the overall birth rate
  is starting to slow.
• Frank Notestein developed a theory called the
  Theory of Demographic Transition that explains
  this.
• According to the Theory of Demographic
  Transition, as countries become more developed,
  their population sizes go through 3 stages.

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The Demographic Transition

• During the 1st stage, birth and death are high
  since the country is pre-industrialized.
• During the 2nd stage, birth rates remain high,
  but death rates drop (due to increases in health
  care and technology) and the population grows
  VERY rapidly.
• During the 3rd stage, birth rates fall until they
  are almost equal with death rates, and the
  population growth slows down or completely stops.
• There are many reasons why the population slows
  in the 3rd stage, such as the education of the
  mother, the need for fewer workers, and the
  greater expense to raise each child.

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A Demographically Divided World

• The world is clearly divided demographically
  between the developed and developing nations.
• The developed nations are all in the 3rd stage of
  demographic transition and are no longer
  increasing very much in size.
• In the U.S., almost all of our population
  increase will be due to immigration.
• In Japan and Germany, they have negative growth
  rates and their population is shrinking as people
  have fewer and fewer kids!
• The developing nations, on the other hand, are
  stuck in the 2nd stage, and are having massive
  population growth.
• Their birth rates have remained high and their
  death rates have dropped, so their population is
  exploding!

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A Demographically Divided World

• The difference in populations between the
  developed and developing nations can best be
  shown using a population pyramid.
• In the developed nations, the pyramid is rather
  flat, with the population getting smaller with
  age (both young and old).
• In the developing nations, the pyramid is very
  steep, with the population getting MUCH BIGGER as
  it gets younger!

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Ch. 13-3 Problems Related To Population Growth

• Key Terms
• Environmental Refugees

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California Content Standards for Science
Addressed

• Life Science
• 6(b) Students know how to analyze changes in an
  ecosystem resulting from changes in climate,
  human activity, introduction of nonnative
  species, or changes in population size.
• 6(c) Students know how fluctuations in population
  size in an ecosystem are determined by the
  relative rates of birth, immigration, emigration,
  and death.

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Ch 13-3Why Do I Need To Know This?

• Because around the world many countries are
  struggling to deal with overpopulation which is
  resulting in disease, starvation, and wars.
• Because even though those problems may not be
  happening here in the United States, we are often
  affected by it as wars threaten countries that we
  support or prevent us from trading for resources.
• Because we are all part of humanity and have an
  obligation to help people when they are suffering.

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Key Sections Ch. 13-3

• Problems Related To Population Growth
• A Shortage of Fuelwood
• Water That Kills
• The Urban Crisis
• Social Unrest
• Environmental Refugees
• Solving Problems Related To Population Growth
• Overconsumption in Developed Nations

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Problems Related To Population Growth

• There are many problems related to rapid
  population growth, especially in the developing
  nations.
• These include
• Starvation
• Disease
• Wars
• Urban Problems
• Social Unrest/ Displacement of People

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A Shortage of Fuelwood

• Around the world, the most common limiting
  resource for humans is fuelwood.
• Fuelwood is very important as it allows us to
  cook food, boil water, and heat homes.
• Without fuelwood, people are much more likely to
  die of disease or malnutrition as a result of
  parasites.

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Water That Kills

• Access to freshwater is also a major limiting
  resource.
• We need water not only for drinking, but also for
  cleaning clothes and taking away sewage.
• As population sizes increase, the amount of water
  pollution increases, leaving more pollution and
  less freshwater.
• Every year, over 10,000,000 people die from
  curable diseases that they get from polluted
  water.
• In very crowded areas, epidemics of diseases such
  as cholera, dysentery, and typhoid fever.

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The Urban Crisis

• As the population swells, cities often become
  overwhelmed with people and do not have enough
  places for people to live.
• This leads to a rise in homelessness and crime in
  the city.
• In many places, the population is rising so
  rapidly that people are building shanty-towns on
  the outskirts of cities just to have places to
  live.

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Social Unrest

• As populations soar, it can lead to economic
  problems, riots, civil wars, international wars,
  and genocide.
• Most of the wars in Africa and Asia have to due
  with overpopulation and competing groups trying
  to control the country or resources.
• Presently, there are about 70 active wars going
  on around the world killing about 2 million
  people a year.
• Even in the United States, the largest reason for
  illegal immigration is the overpopulation in many
  nearby countries.

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Environmental Refugees

• As the human population continues to grow, we are
  altering the environment in many negative ways.
• Due to pollution, industrial accidents,
  over-farming, etc. we have made many places on
  the Earth uninhabitable.
• As a result, people are being driven from their
  homes to find new places to live and as such, are
  considered environmental refugees.

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Solving Problems Related To Population Growth

• If humans are going to find a way to maintain our
  standard of living, we must find ways to slow the
  growth of the human population.
• Studies have shown that the best way to limit the
  population growth is to educate mothers and to
  delay the onset of childbirth until after the
  mother is age 20.
• Family planning to space out the birth of
  children every 2 to 3 years is also very
  important to slowing the worldwide population
  growth.
• Birth control is often a component to family
  planning, but often is not used by many people
  around the world due to religious beliefs.

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Overconsumption in Developed Nations

• As much as the developing nations need to reduce
  their populations, the developed nations need to
  reduce their consumption.
• Developed nations account for 21 of the worlds
  population but consume about 75 of the worlds
  resources and create about 80 of the worlds
  trash and pollution.
• The average person in the United States uses
  about 10 times the goods and services as a person
  in a developing country.
• If we reduce the amount of resources that we use,
  we can increase the amount available for everyone
  around the world.