1. Chapter 19: Population Ecology

2. Population
A population is a group of organisms that belong to the same species and live in a particular place at the same time.
Populations can be measured in terms of size, density, dispersion, growth rate, age structure, and survivorship.

3. Properties of Populations
Population Size
A population’s size is the number of individuals that the population contains.
Population Density
Density is a measure of how crowded the population is.
Age Structure
A population’s age structure indicates the percentage of individuals at each age.

4. Properties of Populations, cont.
Dispersion
Dispersion describes the distribution of individuals within the population and may be random, uniform, or clumped.

5. Populations can increase, decrease, or stay the same over time
Population Dynamics
Populations can increase, decrease, or stay the same over time

6. What do you think might affect a population’s growth and size?

7. Resources, Space, Predators, Disease, and Habitat
Key Point #1: A Limiting Factor is something that keeps a population from growing infinitely
Think:
What are the 5 major limiting factors?
Resources, Space, Predators, Disease, and Habitat

8. There are 2 different types of limiting factors

9. 1. Density-Independent Factors
Key Point #2: Density-independent factors are not affected by the population size
Do not depend on the number of individuals present in an area.
Examples: unusual weather, natural disasters, and seasonal cycles

10. 2. Density-Dependent Factors
Key Point #3: Population-limiting factors, such as competition, are density-dependent because the effect on each individual depends on the number of other individuals present in the same area.
Examples: competition, disease, and predation

11. You Try: Density-Dependent or Independent?

12. Predation

13. Weather Patterns

14. Disease

15. Competition for Resources

16. Survivorship Curves
Patterns of Mortality
Populations show three patterns of mortality or survivorship curves:
Type I (low mortality until late in life)
Type II (constant mortality throughout life)
Type III (high mortality early in life followed by low mortality for the remaining life span).

17. Survivorship Curves, cont.
Type I = large mammals (i.e., humans, elephants)
Type II = birds, lizards, rodents
Type III = fish, insects

18. Population Growth Rate
Scientists define the growth rate of a population as the amount by which a population’s size changes in a given time.
Population Size
Birth rate - death rate = growth rate
If the birth rate increases, the population increases
If the death rate increases, the population decreases

19. Exponential Growth
The exponential model describes perpetual growth at a steady rate in a population.
The model assumes constant birth and death rates and no immigration or emigration.
Assumes unlimited resources

20. Logistic Growth
In the logistic model, birth rates fall and death rates climb as the population grows.
When the carrying capacity is reached, the number of individuals the environment can support is reached and population growth becomes stable.

21. Logistic Growth, cont.
Limiting factors (i.e., food, water, space) will limit a population’s growth, so it cannot exceed carrying capacity

22. You Try: Exponential or Logistic?

23. You Try: Exponential or Logistic?

24. You Try: Exponential or Logistic?