1. Ch. 5 Populations

2. Ch. 5 Outline 5-1: How Populations Grow
Characteristics of Populations
Population Growth
Exponential Growth
Logistic Growth
5-2: Limits of Population Growth
Density-Dependent Factors
Density-Independent Factors
5-3: Human Population Growth
Patterns of Population Growth

3. Characteristics of Populations
Geographic Distribution
Density
Growth Rate
Age Structure
Geographic Distribution (or range) is the area inhabited by a population
Population density: the number of individuals per unit area

4. Population Growth Three factors can affect population size:
The number of births
The number of deaths
The number of individuals leaving or entering the population
A population is growing when its birthrate is greater than its death rate.

5. Population Growth
The movement of Individuals also affects population size.
Immigration: The movement of individuals to an area
Emigration: The movement of individuals out of an area
What might cause the movement of individuals either to or from and area?
Food Supply
Finding a mate

6. Exponential Growth
Exponential growth: occurs when individuals in a population reproduce at a constant rate
A population will grow exponentially under ideal conditions:
No predation
Plenty of Food and Space
The graph of a population growing exponentially:
J-shaped Curve
Bacteria often grow exponentially

7. Exponential Growth Curve

8. Logistic Growth
Logistic Growth: occurs when a population’s growth slows or stops following a period of exponential growth
Takes into account a limited amount of resources
Graph of Logistic Growth:
S-shaped Curve
The largest number of individuals that a given environment can support is called the carrying capacity.

9. Limits to Population Growth
What causes population size to decrease?
Limiting Factors: a factor that causes population growth to decrease
Examples of Limiting Factors:
Competition
Predation
Parasitism
Drought (or other climate extremes)
Human Disturbances

10. Density-Dependent Factors
A limiting factor that depends on population size is called a density-dependent factor.
They only become limiting when the population density reaches a certain level. (They don’t affect small, scattered populations)

11. Examples of Density-Dependent Factors
Competition
When populations are crowded, organisms begin competing for food, space, mates, sunlight, etc…
Competition between two different species also exists  leads to adaptations and natural selection (EVOLUTION!!!)
Predation
The predator-prey relationship is one of the best known mechanisms for population control.
Ex. Moose-wolf population near Lake Superior

12. Examples of Density-Dependent Factors
Parasitism and Disease
Parasites take nourishment at the expense of their host, often weakening them (leading to death).

13. Density-Independent Factors
Density-Independent Factors: affect all populations in similar ways, regardless of the population size.
Examples:
Weather/seasonal changes
Natural disasters
Human Activities

14. Historical Overview
For most of history, the human population has grown very slowly
About 500 years ago, agriculture and industry made life easier and the population growth rate increased.
With the Industrial Revolution came improved medical care and increased sanitation, which lead to exponential human population growth.

15. Patterns of Population Growth
The Earth cannot sustain exponential population growth forever. It DOES have a carrying capacity. (Resources are limited!)
Demography: the study of human populations
Attempts to explain how they will change over time
Birthrates, death rates, and age structures of populations help predict why some countries have high growth rates while others have low growth rates.

16. Patterns of Population Growth
In the last century, Japan, the United States, and much of Europe have slowed their population growth.
Why?
With improved nutrition, sanitation, and medical care, the death rate was slowing and the birthrate was still high (cause an increase in the population). BUT, as societies become more modern, families are tending to have less children (as education level and standards of living increase).

17. Patterns of Population Growth
However, the worldwide population is still growing exponentially.
Population growth also depends on age structure.
How many people of different ages make up a population?
Age-Structure Diagrams: Graph the number of people in different ages in a population
Ex: USA vs. Rwanda.