1. Introduction to Populations

2. A population is all the members of a species living in the same place at the same time.
Examples:
What is a population?

3. A population’s density is the number of individuals per unit area or volume, such as the number of bass per cubic meter of water in a lake.

4. Growth Rate How do you know if a population is growing?
Births – Deaths = Growth rate
Growth Rate

5. Growth rates can be: Positive = more births than deaths
Negative = more deaths than births
Zero (no growth) = births and deaths are equal

6. Exponential vs. Logistic growth rates
Exponential growth (J curve) occurs in nature only when populations have plenty of food and space, and have little or no competition or predators.
Examples: growth of most bacteria, a population of rats in a large urban area, a cat and her offspring can have 40,000 cats in 7 years
Exponential vs. Logistic growth rates

7. Logistic growth (S curve) occurs when a population is limited to a particular size. These limits usually occur because of a lack of resources.
Examples: most human populations, a population of lions in Kenya, a population of yeast used to make bread

8. Population Limits What is carrying capacity?
The maximum population that the ecosystem can support indefinitely
Population Limits

9. What are limiting factors?
A natural resource that has potential to limit a population’s size
Density dependent limiting factors are those that cause death more quickly in crowded or densely populated areas.
Example: food supply, predators, water supply, habitat space, diseases, etc.

10. Density independent limiting factors are those that kill off individuals of a population regardless of the population’s size or density.
Examples: weather, climate, natural disasters (forest fires, volcanic eruptions, hurricanes, tornadoes, tsunamis), etc.

11. Practice!
a. A lion and a cheetah attempt to occupy the same niche. The more aggressive lion survives; the cheetah does not.
b. Coyotes cross the winter pack ice and enter Newfoundland. The moose population starts to decline.
c. A severe frost wipes out 50% of the coffee crop in Brazil.
d. A forest fire destroys much of the wildlife in an area of Manitoba.
e. Due to severe overcrowding in an Asian village, many children do not survive to reach maturity.
f. Since lynx prey on hares, an increase in the hare population causes an increase in the lynx population.