1. Ecology
POPULATIONS

2. Objectives
Identify factors that limit population size.
Differentiate between density-dependent and density-independent factors.

3. The following standards will be addressed:

4. KEY CONCEPT Populations grow in predictable patterns.

5. Changes in a population’s size are determined by immigration, births, emigration, and deaths.
The size of a population is always changing.
Four factors affect the size of a population.
immigration
births
emigration
deaths

6. Population Growth
Natural populations vary in size from year to year.
Three factors affect population size:
Number of births
The birth rate.
Number of deaths
The death rate.
Number of individuals entering/leaving
Immigration: movement into a population
Emigration: movement out of a population

7. Birth Rate > Death Rate: Population Grows
Population Growth
Birth Rate > Death Rate:
Population Grows
Birth Rate < Death Rate:
Population Declines
Birth Rate = Death Rate:
Population Steady

8. Population growth is based on available resources.
Exponential growth is a rapid population increase due to an abundance of resources.

9. Exponential Growth
If a population has abundant space and food, and is protected from predators and diseases, then the population will multiply and the size will increase.
Populations will exhibit exponential growth.
Shown via an exponential model.

10. Logistic Growth The Earth is NOT covered by unlimited organisms-Why?
There are not abundant resources.
When a population’s growth stops or slows following a period of exponential growth, it is now considered logistic growth (logistic model).

12. Carrying capacity is the maximum number of individuals in a population that the environment can support.
A population crash is a dramatic decline in the size of a population over a short period of time.

13. Ecological factors limit population growth.
A limiting factor is something that keeps the size of a population down.
There are two types:
density-dependent
density-independent

14. Density-dependent limiting factors are affected by the number of individuals in a given area.
predation
competition
parasitism and disease

16. Density-independent limiting factors limit a population’s growth regardless of the density.
unusual weather
natural disasters
human activities