Finding Gold in a Costa Rican Cloud Forest Levels of

Environmental Science Ch. 4 Population Ecology &

Ch. 8 Human Population

Chapter FOUR: Population Ecology

Finding Gold in a Costa Rican Cloud Forest

• Golden toads lived in Costa Rica’s

Monteverde cloud forest.

• Golden toads were first described in

1964. They were extinct by 1989.

Talk About It Why is the extinction of the golden

toad a global concern?

Talk About It Why is the extinction of the golden

toad a global concern?

Levels of Ecological Organization

• The study of how organisms interact with each other and with their environments

• Scientists study ecology at various levels of organization.

Lesson 4.1 Studying Ecology

Why Do I Need To Know This?

1. Because we need to understand how all populations grow in order to understand what will happen if the human population continues to grow.

2. 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.

3. Because humans may already be at their carrying capacity for the entire planet!

Population Size

Lesson 4.2 Describing Populations

• The number of individuals in a population at a given time

• Sudden and dramatic decreases in population size can indicate an unhealthy population headed toward extinction.

• Ecologists often use sampling techniques to estimate population size.

Did You Know? The passenger pigeon

was once North America’s most

abundant bird. Hunting drove them to

extinction in less than 100 years.

Did You Know? The passenger pigeon

was once North America’s most

abundant bird. Hunting drove them to

extinction in less than 100 years.

Counting Laysan Albatross Nests

How Populations Change In Size• Presently, there are

over 7 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 sustainthis level of population growth on the planet for much longer!

How Populations Change In Size

The Formula that Shows Population Growth Is:

Number of Births Number of Deaths

+ > +Number of Immigrants Number of Emigrants

The Formula that Shows Population Decrease Is:

Number of Deaths Number of Births

+ > +Number of Emigrants Number of Immigrants

How Fast Can A Population Grow?#1• 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 maximumcapacity.

– 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!

Population Density


• Measure of how crowded a population is

• Larger organisms generally have lower population densities.

• Low population density:More space, resources; finding mates can be difficult

• High population density:Finding mates is easier; tends to be more competition; more infectious disease; more vulnerability to predators

Northern pintail ducks

How Fast Can A Population Grow?#2• 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 they 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.

What Limits Population Growth? #1

• 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.

What Limits Population Growth? #2• 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 environmentcan change the carrying capacity for the species.

Logistic Growth and Limiting Factors

Lesson 4.3 Population Growth

• Growth almost always slows and stops due to limiting factors.

• Limiting factors:Environmental characteristics slow population growth and determine carrying capacity.

• Density-dependent:

Influence changes with population density.

• Density-independent:

Influence does not change with population density.

Population Distribution


• How organisms are arranged within an area:

• Random distribution:Organisms arranged in no particular pattern

• Uniform distribution:Organisms evenly spaced

• Clumped distribution:Organisms grouped near resources; most common distribution in nature

Age Structure


• Relative number of organisms of each age group within population

• Can be used to predict future population growth of a population

Sex Ratios


• Proportion of males to females

• Age structure diagrams give information about sex ratios.

• For a monogamous species, the ideal sex ratio is 50:50.

Ch. 8-Part I: A Growing Human Population

Key Terms• Agricultural Revolution

• Hunter-Gatherers

• Demographics

• Fertility Rate

• Infant Mortality

• Life Expectancy

China’s One-Child Policy

• In 1970, the average Chinese woman had about six children.

• Since 1979, China has used a system

of rewards and punishments to

enforce a one-child limit to slow population growth.

• In 2005, there were 32 million more

males than females in China under

the age of 20.Talk About It Is it ethical for governments to limit or

encourage human population growth?

Talk About It Is it ethical for governments to limit or

encourage human population growth?

Ch. 8-Part I:

Why Do I Need To Know This?

1. Because the human population is growing at an alarming rate which is causing global problems!

2. Because at some point the human population will exceed the number of people who can live on the planet (if we haven’t already reached it), and that could lead to major global problems.

3. Because overpopulation affects everything from immigration to economies to wars.

4. 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.

Key Sections Ch. 8-Part I

• A Growing Human Population

• From Hunting and Gathering To

Agriculture

• The Population Continues To Grow

• The Demographic Transition

• A Demographically Divided World

A Growing Human Population• Like a single ecosystem,

the entire Earth has a carrying capacity.

• Scientists are not sure what the planet’s 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.

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.

The Population Continues To Grow• By about 1800, the world’s

population reached about 1 billion people.

• Between 1800 and 1930, the world’s population doubled to 2 billion people!

• By 1975, the world’s population doubled again to 4 billion people!

• The rapid rise in population had to do with improvements in medicine, technology, sanitation and access to freshwater which all greatly increased the average person’s 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.

The Population Continues To Grow

Infant Mortality and Life Expectancy

• Populations are likely to grow when infant mortality is low and life expectancy is high.

• Infant mortality: Number of babies out of 1000 that die during their first year of life

• Life expectancy: Average number of years a person is expected to live

• Population growth rate describes the change in population’s size during a given period of time.

Lesson 8.1 Trends in Human Population Growth

Demography: Describing the Human Population

• Population size:

Number of people

• Population density: Number of people living per mi2 (or per km2)

• Population distribution: How people are distributed within an area

Lesson 8.1 Trends in Human Population Growth

Fertility Rate

Lesson 8.2 Predicting Population Growth

• Total fertility rate: Average number of children a female has during her life

• Replacement fertility rate:The total fertility rate for a nation that would keep its population stable

• For most nations, a replacement fertility rate of 2.1% would keep population size stable. A greater rate would increase population size; a lesser rate would decrease it.

Age Structure• Age structure describes the

relative number of people within different age brackets in a population.

• A population of mostly young people tends to grow. A population of mostly old people tends to shrink.

• A population with equal numbers of young and old tends to remain stable in size.


Sex Ratio• Describes the relative numbers of females and males

• Typical sex ratio for humans is 1.00 females : 1.06 males. For

every

100 females

born, 106 males

are born.

• Human activity

such as migration

can skew sex ratios.


The Demographic Transition• Model that explains a population’s change from high

birthrates and death rates to low birthrates and death rates

– Pre-industrial stage: Birthrates and death rates are high.

– Transitional stage: Birthrates are high but death rates are declining.

– Industrial stage: Birthrates start to decline; death rates stay low.

– Post-industrial stage: Both birthrates and death rates fall to low and stable levels.

Did You Know? Over the past 50 years, worldwide average life expectancy has increased from 46 to 68 years.

Did You Know? Over the past 50 years, worldwide average life expectancy has increased from 46 to 68 years.

• Demographic transitions are the result of economic growth and social changes.

The Demographic Transition #2

Social Factors and Population Growth

• Developing nations:

– Higher fertility, infant mortality,

and death rates

– Lower life expectancy

– Less Technology & Education-

More Blue Collar Workers

– Low per capita resource use

• Developed nations:

– Lower fertility, infant mortality,

and death rates

– Higher life expectancy

– More Technology & Education-

Different types of Workers

– High per capita resource use

Did You Know? On average, 1 American consumes as much natural resources as 5 Chinese or 13 Pakistanis.

Did You Know? On average, 1 American consumes as much natural resources as 5 Chinese or 13 Pakistanis.

A Demographically Divided World #1• The world is clearly divided

demographically between the developedand developing nations.

• The developed nations are all in the 3rd

& 4th 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 1st & 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!

A Demographically Divided World #2

**The Growth rate of human population has slowed from 2.1% to about 1.2%

since the 1960s.


• Some scientists

predict that there will

be

9 billion people on

Earth by 2050, while

others maintain that

the population will

be closer to 10.5 billion.

Ch. 8-Part 2: Problems Related To Population Growth

Key Terms• Fuelwood

• Cholera

• Dysentary

• Typhoid Fever

• Environmental Refugees

• Wealth Gap

• Urban Crisis

Ch 8 – Part 2:Why Do I Need To Know This?

1. Because around the world many countries are struggling to deal with overpopulation which is resulting in disease, starvation, and wars.

2. 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.

3. Because we are all part of humanity and have an obligation to help people when they are suffering.

Key Sections Ch. 8-Part 2

• 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

Environmental Impacts

• The environmental impact of humans depends on the way they live.

• Poorer societies tend to have smaller ecological footprints than affluent societies, but still strain the environment:

– Overwhelmed governments can’t supply clean water or adequate sewage treatment.

– Poverty often leads to land overuse.

– Deforestation, flooding, disease, and habitat loss can become common, as land is cleared for farming.

Lesson 8.3 People and Their Environments

Problems Related To Population Growth

• There are many problems related to rapid population growth, especially in the

developing nations.

• These include:

1. Starvation

2. Disease

3. Wars

4. Urban Problems

5. Social Unrest/ Displacement of People

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 diseaseor malnutrition as a result of parasites.

Water That Kills• Access to freshwater is also a

major limiting resource.

– We need water not only for drinking, but also for cleaningclothes and taking away sewage.

• As population sizes increase, the amount of water pollution increases, leaving more pollutionand less freshwater.

• Every year, over 10,000,000people die from curable diseases that they get from polluted water.

• In very crowded areas, epidemics of diseases such as cholera, dysentery, and typhoid fever.

The Wealth Gap• Currently, the richest 20% of

the world’s people use 86% of its resources.

• As developing nations such as China continue to develop, new environmental problems will emerge, as the need for and use of resources increases.

• Resource availability affects quality of life.


Did You Know? Globally, 1.4 billion people live on less than $1.25 per day, and another 2.6 billion live on less than $2 per day.


Burning of fossil fuels creates a haze of

pollution over the eastern coast of China.

The Urban Crisis• As the population

swells, cities often become overwhelmedwith 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-townson the outskirts of cities just to have places to live.

Social Unrest

• As populations soar, it can lead to economic problems, riots, civil wars, international wars, and genocide.

• Most of the wars in Africaand Asia have to due with overpopulation and competing groups trying to control the country or resources.

• Presently, there are about 70active 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.

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.

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.

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 world’s

population but consume about 75% of the world’s resources and create about 80% of the world’s trash and pollution.

– The average person in the United States uses about 10times 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.

The Wealth Gap• Currently, the richest 20% of the

world’s people use 86% of its

resources.

• As developing nations such as China continue to develop, new

environmental problems will

emerge, as the need for and use

of resources increases.

• Resource availability affects

quality of life.




Burning of fossil fuels creates a haze of

pollution over the eastern coast of China.

Impacts of Technology


–Negative impacts:

• Has enabled resource exploitation

• Has resulted in pollution, biodiversity loss, and climate changes

–Positive impacts:

• Enables longer, healthier, more comfortable lives

• Technologies such as recycling can help reduce environmental impact.

• Renewable energy technology can produce cheap, clean energy.

Solar water pump

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Finding Gold in a Costa Rican Cloud Forest Levels of