1. Biology
Chapter 5

2. Characteristics of Populations
Geographic Distribution – the area inhabited by a population
Population Density – number of individuals per unit area
Growth Rate – an increase or decrease of the number of individuals in a population over time

3. Population Growth/Decline
A population can grow when its birthrate is greater than its death rate
Immigration – movement of individuals into an area
Populations can increase
Animals maybe searching for mates or food
Emigration – movement of individuals out of an area
Populations can decrease
Animals leave to find mates or food

4. Exponential Growth
Under ideal conditions with unlimited resources a population will grow exponentially resulting in a population explosion
Exponential growth is characterized by a J-shaped curve

5. In nature exponential growth does not continue in a population for very long
As resources become less available, the growth of a population slows or stops

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Exponential Growth
Exponential Growth
In the presence of unlimited resources and in the absence of predation and disease, a population will grow exponentially. Both hypothetical graphs show the characteristic J-shape of exponential population growth.
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7. Logistic Growth
Occurs when a population’s growth slows or stops following a period of exponential growth
Logistic growth is characterized by a S-shaped curve

8. initial carrying capacity
new carrying capacity
Fig. 46.6, p. 818
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9. What prevents the world from being overrun with all kinds of living things?
Carrying Capacity – the number of organisms of one species that an environment can support
When a population reaches the carrying capacity of its environment, its growth levels off

10. Limiting Factors
Limiting Factor – a factor that causes population growth to decrease
Density-Dependent Factors – a limiting factor that depends on population size
These factors operate most strongly when a population is large and dense
As populations increase so do these factors
Example: competition, predation, parasitism, disease
Density-Independent Factor – a limiting factor that affects all populations regardless of the population size
Example: natural disasters, storms, floods, drought, pollution

11. Demography – the study of human population growth
For most of human existence, the population grew slowly
Limiting factors kept population sizes low
About 500 years age, the human population began growing more rapidly
Life was made easier and safer by advances in agriculture and industry
Death rates were dramatically reduced due to improved sanitation, medicine, and healthcare, while birthrates remained high
With these advances, the human population experienced exponential growth

12. Historical Overview Human Population Growth
The size of the human population has increased over time. After a long, slow start, the worldwide population grew exponentially following improvements in medicine, sanitation, agriculture, energy use, and technology.
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13. Age Structure
Age-Structure Diagrams – show the population of a country broken down by gender and age group
Population growth depends, in part, on how many people of different ages make up a given population
Demographers can predict future growth using age- structure diagrams

14. Patterns of Population Growth
Slow
Growth
Rapid
Growth
Zero
Growth
Negative
Growth
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15. How can you tell if a population is growing?
If the birth rate is more than the death rate

16. Does it make a difference to population growth if the largest proportion of the population is in one age group?
If a large percent of the population is teenagers and children there is rapid growth
If the percent of people in each category is equal the population is stable