1. Houston Community College/ Southeast
GEOL 1305
Environmental Science
A Study of Interrelationships
14 Edition
Enger & Smith

2. Chapter 7: Populations: Characteristics and Issues
7.1 Population Characteristics
7.2 A Population Growth Curve
7.3 Factors That Limit Population Size
7.4 Categories of Limiting Factors
7.5 Carrying Capacity
7.6 Reproductive Strategies and Population Fluctuations
7.7 Human Population Growth

3. Outline 7.8 Human Population Characteristics and Implications
7.9 Factors That Influence Human Population Growth
7.10 Population Growth Rates and Standard of Living
7.11 Hunger, Food Production, and Environmental Degradation
7.12 The Demographic Transition Concept
7.13 The U.S. Population Picture
7.14 What Does the Future Hold?

4. 7.1 Population Characteristics
A population is a group of individuals of the same species inhabiting the same area.
Genetic differences commonly exist within different populations of a given species
Natality: The number of individuals added to a population through reproduction over a particular time period.
Birth Rate = Humans born per 1,000 individuals per year.
Mortality: The number of deaths in a population over a particular time period.
Death Rate = Humans died per 1,000 individuals per year.
Population growth rate is the birthrate minus the death rate.
In human population studies it is often expressed as a percentage of the total population.

5. Factors of population change
Birth rate B is the number of births per 1000 individuals per year (in the US = 15).
Death rate D is the number of deaths per 1000 indv. Per year (in the US = 9).
Immigration rate I is the number of immigrants per 1000 citizens per year (in the US = 3).
Emigration rate E is the number of Emigrants per 1000 of citizens per year.
4. The Population Rate of Change R is the percentage increase or decrease in population per year. R = [(B-D) + (I-E)] . 100%
R in USA = [( ) + ( )] . 100%
= [ ] . 100% = % = 0.9%.

6. Population Characteristics
Effect of birthrate and death rate on population size

7. Population Characteristics
A survivorship curve shows the proportion of individuals likely to survive to each age.
Three types of survivorship curves can be recognized:
Species with high mortality in young.
Species with mortality equitable among age classes.
Species with mortality high only in old age.

8. Sex Ratio and Age Distribution
Sex ratio refers to the relative number of males and females in a population.
The number of females is important because females determine the number of offspring produced in sexually reproducing populations.
Age distribution is the number of individuals of each age in the population.
Age distribution greatly influences the population growth rate.

9. Population Characteristics
Age distribution in human populations

10. Population Density and Spatial Distribution
Population density is the number of individuals per unit area.
High population density injures all individuals within the population because they compete severely for necessary resources.
Dispersal: Movement of individuals from densely populated locations to new areas.
Emigration: Movement from an area.
Immigration: Movement into an area.
US population density = 300 m / 3.7 m mi2 = 81 indv./mi2
Houston population density = 2 m / 600 mi2 = 3300 indv/mi2.

11. 7.2 A Population Growth Curve
Biotic potential is the inherent reproductive capacity of a species (biological ability to produce offspring)
Several factors influence the biotic potential:
The age at which reproduction begins.
The fraction of the life span during which an individual is capable of reproducing.
The number of reproductive periods per lifetime.
The number of offsprings produced during each period of reproduction.
Generally, larger organisms (such as whales and elephants) have the smallest biotic potential, whereas microorganisms have the greatest one.

12. Population Growth Curve
Population growth follows a pattern consisting of a lag phase, an exponential growth phase, a deceleration phase, and a stable equilibrium phase.
Lag Phase: This is the first portion of the curve; slow population growth.
Exponential Growth Phase (Log Phase): More organisms are reproducing, causing accelerated growth; this continues as long as birth rate exceeds death rate.
Deceleration Phase: The population growth rate slows as the death rate and birthrate come to equal one another.
Stable Equilibrium Phase: The death rate and birth rate become equal and the population stops growing.

13. A Population Growth Curve
A typical population growth curve

14. 7.3 Factors That Limit Population Size
Factors that prevent unlimited population growth are known as limiting factors.
All of the different limiting factors that act on a population are collectively known as environmental resistance.
Extrinsic limiting factors are those that come from outside the population.
Predators
Loss of food source
Lack of sunlight
Accidents of nature

15. Factors That Limit Population Size
Intrinsic limiting factors are those factors that originate within the population and exercise control over it.
Behavioral changes amongst the population cause lower birthrates and higher death rates.
Density-dependent limiting factors are those that become more effective as the density of the population increases.
Density-independent limiting factors are population-controlling influences that are not related to the density of the population.

16. Density-Dependent factors
Density-Dependent factors are the factors that influenced by changes in population density:
Competition: As population density increases, so does competition for resources (food, water, space, sunlight…).
Predation: When a certain prey population increases, the population of their predators increases. When a certain predator population increases, the prey population decreases.
3. Disease: Parasites live off their hosts, weakening them and causing diseases. Crowding helps parasites travel from one host to another. Disease effects large, concentrated populations more than small, scattered ones.

17. Density-Independent factors
Density-Independent factors are the factors NOT influenced by changes in population density:
They are typically abiotic:
a. Random weather events that reduce population size, such as severe blizzards and hurricanes.
b. Fire.
c. Human intervention.
d. Pests.

18. 7.5 Carrying Capacity
Carrying capacity is the maximum sustainable population for an area.
It is not an inflexible number; it can be influenced by environmental differences such as:
Successional changes
Climate variations
Disease epidemics
Forest fires, floods, or natural disasters
Nutrient levels in aquatic ecosystems

19. 7.6 Reproductive Strategies and Population Fluctuations
Species can be divided into two broad categories based on their reproductive strategies:
K-strategists: Organisms that typically reach a stable population as the population reaches the carrying capacity.
r-strategists: Typically, these are small organisms that have a short life, produce many offspring, exploit unstable environments, and do not reach a carrying capacity.

20. Reproductive Strategies and Population Fluctuations
K-strategist characteristics include:
Usually occupy relatively stable environments
Large organisms
Long-lived
Produce few offspring
Provide substantial parental care
Reproductive strategy is to invest a great deal of energy in producing a few offspring that have a good chance of living to reproduce.
K-strategists are controlled by density-dependent limiting factors.

21. Reproductive Strategies and Population Fluctuations
r-strategist characteristics include:
Small, short-lived organisms
Produce many offspring
Little if any parental care
Exploit unstable environments
Usually do not reach carrying capacity (boom-bust cycles)
Reproductive strategy is to produce large numbers of offspring to overcome high mortality.
r-strategists are controlled by density-independent limiting factors.

22. 7.7 Human Population Growth
The human population growth curve has a long lag phase followed by a sharply rising exponential growth phase that is still rapidly increasing.
A major reason for the increasing human population growth rate is an increase in medical care, and a consequential decrease in death rates.

23. Human Population Growth
Historical human population growth

24. Human Population Growth
The doubling time for the human population is calculated by:
70 / annual rate of increase (%)
( 70 / 2.0% = 35 years )

25. 7.8 Human Population Characteristics and Implications
The world can be divided into two segments based on economic development.
More-developed countries typically have per capita income exceeding $10,000.
Europe, Canada, the U.S., Japan, Australia, New Zealand
Combined population of 1.2 billion
Relatively stable populations
Expected to grow 3% by 2050

26. Human Population Characteristics and Implications
Less-developed countries typically have a per capita income less than $5,000.
All other remaining countries of the world
Combined population of 5.3 billion
Nearly 3 billion live on less than $2 per day
High population growth rates
Expected to grow 52% by 2050 (8 billion people, or 86% of the world’s population)

27. Human Population Characteristics and Implications
Population growth and economic development

28. Human Population Characteristics and Implications
Human population growth is tied to economic development and is a contributing factor to nearly all environmental problems.
Population density relates the size of the population to available resources.
Countries with abundant resources can sustain higher population densities than resource-poor countries.
The degree of technological development and affluence is also significant; people in highly developed countries consume huge amounts of resources.

29. Human Population Characteristics and Implications
The ecological footprint is a measure of the land area required to provide the resources and absorb the wastes of a population.
Most of the more-developed countries of the world have a much larger ecological footprint than is represented by their land area.
Japan is highly developed but has few resources; its ecological footprint is 5 times larger than its locally available resources.
The ecological footprint of the U.S. is 1.5 times locally available resources.

30. 7.9 Factors That Influence Human Population Growth
Humans, unlike other kinds of organisms, are influenced by social, political, economic, and ethical factors.
We can make conscious decisions based on the likely course of events and adjust our lives accordingly.

31. Factors That Influence Human Population Growth
Biological Factors
Demography is the study of populations and their characteristics, how those characteristics affect growth, and the consequences of that growth.
The most important determinant of the rate at which human populations grow is related to how many women in the population are having children and the number of children each woman will have.
The total fertility rate of a population is the number of children a woman has during her lifetime.

32. Factors That Influence Human Population Growth
Biological Factors
A total fertility rate of 2.1 is known as replacement fertility; parents produce 2 children who will replace the parents when they die.
Zero population growth is when the birth rate equals death rate.
The age distribution is the number of people of each age in the population.

33. Factors That Influence Human Population Growth
Social Factors
Reducing fertility rates would be advantageous, especially in LDCs, but not everyone agrees.
Several factors (religious, traditional, social, and economic) influence the number of children a couple would like to have.
The major social factors determining family size are the status and desires of women in the culture.
In male-dominated cultures, traditional role of women is to marry and raise children.

34. Factors That Influence Human Population Growth
Social Factors
Early marriages foster high fertility rates.
In Africa, 17% of births are to women in the year-old range.
Total Fertility Rate of 5.0%
Childrearing practices also influence population growth rates.
In countries where breast feeding is practiced, several benefits accrue.
Breast milk is an excellent source of nutrients and antibodies.
During the months a woman is breast feeding, she is less likely to become pregnant again.

35. Factors That Influence Human Population Growth

36. Factors That Influence Human Population Growth
Social Factors
Lack of education opportunities for women reduces their options.
When level of education increases, fertility rates fall.
Financial independence leads to marriage later in life.
Better-educated women are more likely to have access to and use birth control.
In some cultures women desire large families:
In countries where infant mortality is high, it is traditional to have large families since several of a woman’s children may not live to adulthood.
Parents are more secure when there are many children to look after their own needs in old age.

37. Factors That Influence Human Population Growth
Economic Factors:
In less developed countries, the economic benefits of children are extremely important.
Even young children can be given jobs that contribute to the family economy, such as protecting livestock, gathering firewood, or carrying water.
In the developed world, large numbers of children are an economic drain.
They are prevented from working.
They must be sent to school at great expense.
They consume large amounts of the family income.

38. Factors That Influence Human Population Growth
Political Factors
Governments can either reward or punish high fertility rates.
Several European countries are concerned about low birth rates and have instituted policies to encourage couples to have more children.
Paid maternity leave and guaranteed job availability upon the mother’s return to work.
Childcare facilities make it possible for both parents to work.
Child tax deductions provide an indirect payment to families.
Most developing countries are concerned that population growth is too rapid and have instituted programs to limit growth:
They provide information on family planning and maternal and child health.
Sometimes governments provide free or low-cost contraceptives.
One-child policy in China

39. Factors That Influence Human Population Growth
Immigration Policies
Birthrates are so low in some countries that immigration is encouraged to offset a potential decline in the number of working-age citizens.
Developed countries are under intense pressure to accept immigrants.
The higher standard of living is a magnet for refugees or people who seek a better life than is possible where they currently live.

40. Population Growth Rates and Standard of Living
There appears to be an inverse relationship between a country’s growth rate and its average standard of living.
Standard of living is a difficult concept to quantify since various cultures have different desires.
Factors usually included in an analysis of standard of living:
Economic well-being
Health conditions
Social status and mobility

41. Population Growth Rates and Standard of Living
Standard of living and population growth in three countries

42. 7.11 Hunger, Food Production, and Environmental Degradation
As human population grows, so does the demand for food.
Most people in developed countries must purchase their own food.
Most people in less-developed countries must grow their own food.
Human populations can only increase in size if other plant and animal populations decrease in size.

43. Hunger, Food Production, and Environmental Degradation
People in less-developed countries generally feed at lower trophic levels than those in the developed world.
People in less-developed countries must eat plants themselves instead of feeding the plants to animals and eating the animals.
A lack of protein in the diet can lead to malnutrition.
Many people in more-developed countries suffer from over-nutrition.
50% of North Americans are overweight, and 25% are obese.

44. 7.12 The Demographic Transition Concept
Demographic transition is a model of population growth based on historical, social, and economic development of Europe and North America.
Initially, countries have a stable population (high birth and death rates).
The death rate falls and the population grows.
Industrialization occurs and the birth rate falls.
Death rates and birth rates find equilibrium (low birth rates and low death rates).

45. The Demographic Transition Concept

46. The U.S. Population Picture
United States population had a post-war baby boom period, significantly affecting population trends.
1947–1961: birthrates were much higher than today.
This created a population bulge.
As members of this group have raised families, they have had a significant influence on U.S. population growth and trends.
Legal and illegal immigration significantly influences future population growth trends.

47. 7.14 What Does the Future Hold?
We must remember that interactions with other species and with other humans will help determine our carrying capacity.
Four basic factors are involved in this consideration:
Available raw materials
Available energy
Waste disposal
Interactions with other organisms

48. What Does the Future Hold?
Available raw materials
This issue is not limited to the amount of food available.
We are also dependent on technology.
Our lifestyles are tied to use of other resources such as irrigation water, genetic research, and antibiotics.
Available energy
This issue is similar to that of raw materials.
Increases in energy efficiency and the development of renewable fuels can reduce dependence on fossil fuels.

49. What Does the Future Hold?
Waste disposal
Pollution is the waste product of human activity.
Lack of adequate sewage treatment and safe drinking water causes large numbers of deaths.
Interactions with other organisms
We are not the only species of importance.
Converting land to meet our needs displaces other species from their habitats.
What today seems like an unimportant organism may one day be seen as an important link to our own survival.

50. What Does the Future Hold?
Social Factors Influence Human Population
Current technology and medical knowledge are available to control human population growth and improve the health of the people of the world.
But humans are social animals who have freedom of choice and frequently do not do what is considered “best” from an unemotional, uninvolved, biological point of view.
People make decisions based on history, social situations, ethical and religious considerations, and personal desires.

51. What Does the Future Hold?
If the world continues to grow at its current rate, population will surpass 9.4 billion by 2058.
The human population is subject to same biological constraints as other species.
The human population will ultimately reach a carrying capacity and stabilize.
Disagreement about exact size and primary limiting factors