1. Chapter 5 Populations
5-1
How Populations Grow

2. How Populations Grow Characteristics of Populations
4 important characteristics of a population
Geographic distribution
Density
Growth rate
Age structure

3. Geographic Distribution
Geographic distribution, or range, is a term that describes the area inhabited by a population.
Ranges can very enormously in size

4. Population Density
Population density is the number of individuals per unit area.
The population of saguaro cactus in the desert plant community has a low density, whereas other plants in that community have a relatively high density.

5. Populations Growth Three factors can affect population size:
number of births
the number of deaths
the number of individuals that enter or leave the population.
* Simply put, a population will increase or decrease in size depending on how many individuals are added to it or removed from it

6. Immigration & Emigration
the movement of individuals into an area, is another factor that can cause a population to grow.
Emigration
the movement of individuals out of an area, can cause a population to decrease in size.

7. Word Origin
Immigration is formed from the Latin prefix in-, meaning “in,” and migrare, meaning “to move from one place to another.
If the Latin prefix e- means “out,” then which of the following means “migration out”?
A.) emigration
B.) migration
C.) Immigration

8. Age Structure
The number of males and females of each age a population contains.
Age structure greatly effects reproduction

10. Exponential Growth
When the size of each generations offspring is larger than the generation before it this is exponential growth.
If a population has abundant space and food, and is protected from predators and disease, then organisms in that population will multiply and the population size will increase.
Under ideal conditions where resources with unlimited resources.

12. Exponential Growth
Exponential growth occurs when the individuals in a population reproduce at a constant rate.
Under ideal conditions with unlimited resources, a population will grow exponentially.

13. Checkpoint
Which of the following is NOT a condition for a population to reach exponential growth?
A.) presence of unlimited resources
B.) Absence of predation and disease
C.) movement of individuals out of the population

14. Logistic Growth
Logistic growth occurs when a population's growth slows or stops following a period of exponential growth.
As resources become less available, the growth of a population slows or stops. The general, S-shaped curve of this growth pattern, is called logistic growth.

17. Carrying Capacity
The maximum number of individuals of a particular species that a given environment can support.

18. Review
List four characteristics that are used to describe a population. What factors can change a population's size? What is the difference between exponential growth and logistic growth?

19. Limits to Growth
Limiting factor – a factor that controls the growth of a population.
Density dependent
Density independent
Limiting factors determine the carrying capacity of an environment for a species.

20. Density- Dependent Factors
Limit a population when the number of individuals reach a certain level
Competition for food, water, space, sunlight, etc.
Predation and Herbivory – populations cycle up and down

21. Wolf/Moose graph
Moose
Wolves

22. Density- Dependent Factors Continued
Parasitism + disease – the denser the population the easier it spreads
Stress from overcrowding – can lower birth rates, higher death rates, can cause mothers to neglect young, even lead to emigration

23. Density -Independent Factors
Affect all populations in similar ways regardless of size and density
Weather, natural disasters, seasonal change, human interventions (dams, logging, housing developments)

24. Populations usually decrease dramatically after such an event
Can be permanent + cause extinction

25. Historical Overview
For most of human existence, the population grew slowly because life was harsh. Food was hard to find. Predators and diseases were common and life-threatening.

26. Historical Overview
These limiting factors kept human death rates very high. Until fairly recently, only half the children in the world survived to adulthood.
Because death rates were so high, families had many children, just to make sure that some would survive.

27. Exponential Human Population Growth
As civilization advanced, life became easier, and the human population began to grow more rapidly. That trend continued through the Industrial Revolution in the 1800s.

28. The Predictions of Malthus
This kind of exponential growth could not continue forever.
Two centuries ago, English economist Thomas Malthus suggested that only war, famine, and disease could limit human population growth.
Malthus thought that human populations would be regulated by competition (war), limiting resources (famine), parasitism (disease), and other density-dependent factors.
Malthus’s work was vitally important to the thinking of Charles Darwin.

29. Patterns of Human Population Growth
Birthrates, death rates, and the age structure of a population help predict why some countries have high growth rates while other countries grow more slowly.
The scientific study of human populations is called demography. Demography examines characteristics of human populations and attempts to explain how those populations will change over time.

30. The Demographic Transition
To explain this shift, demographers hypothesize that these countries have completed the demographic transition, a dramatic change from high birthrates and death rates to low birthrates and death rates.

31. The Demographic Transition
Three stages
Stage I, birthrates and death rates are high for most of history.

32. The Demographic Transition
In Stage II, advances in nutrition, sanitation, and medicine lead to lower death rates.
Birthrates remain high for a time, so births greatly exceed deaths and the population increases exponentially.

33. The Demographic Transition
During Stage III, as the level of education and living standards rise, families have fewer children and the birthrate falls; population growth slows.
The demographic transition is complete when the birthrate meets the death rate, and population growth stops.

34. The Demographic Transition
So far, the United States, Japan, and Europe have completed the demographic transition.
Parts of South America, Africa, and Asia are passing through Stage II.
A large part of ongoing human population growth is happening in only ten countries, with India and China in the lead.

35. The Demographic Transition
Globally, human population is still growing rapidly, but the rate of growth is slowing down.
Our J-shaped growth curve may be changing into a logistic growth curve.

36. Age Structure and Population Growth
To understand population growth in different countries, we turn to age-structure diagrams.
These diagrams compare the age structure of the U.S. population with that of Guatemala.

37. Age Structure and Population Growth
In the United States, there are nearly equal numbers of people in each age group.
This age structure predicts a slow but steady growth rate for the near future.

38. Age Structure and Population Growth
In Guatemala, on the other hand, there are many more young children than teenagers, and many more teenagers than adults.
This age structure predicts a population that will double in about 30 years.

39. Age diagram US – slow but steady growth rate predicted
Guatemala – predicts population that will double in about 30 years.

40. Future Population Growth
To predict how the world’s human population will grow, demographers consider many factors, including the age structure of each country and the effects of diseases on death rates—especially AIDS in Africa and parts of Asia.

41. Future Population Growth
Current data suggest that global human population will grow more slowly over the next 50 years than it grew over the last 50 years.

42. Future Population Growth
9 billion predicted by 2050
What will stop/slow the growth?