1. Populations

2. Populations
Populations are groups of individuals that belong to the same species and live in the same area
There are three important characteristics of populations…

3. Population Characteristics
Geographic Distribution –
what area does the population inhabit?
Density –
# of individuals concentrated in the area
Growth Rate –
how slowly or quickly a population grows

4. Population Characteristics
Three factors affect population size:
The number of births
The number of deaths
The number of individuals that enter or leave

5. Immigration versus Emigration

6. Population Growth
Exponential Growth – when individuals of a population reproduce at a constant rate.
Occurs only under IDEAL conditions
J-curve plot

9. Population Growth
Logistic Growth – when growth slows or stops following exponential growth
Occurs when resources become less available
Looks like an “S”- shaped curve

11. Carrying Capacity…
the maximum amount of individuals of a population that an environment can support.
Generally when birthrate = deathrate

12. Limiting Factor (LF)
Affects an organism’s ability to survive and causes population growth to decrease
What are some examples?

13. Limiting Factor (LF)
Density DEPENDENT – factors that depend on population size
Competition (resources can become scarce)
Disease: some examples include Pfisteria, Dutch elm disease, AIDS
Predation
Parasitism

15. Limiting Factor (LF)
Density INDEPENDENT – factors that affect all populations regardless of size
Ex. Natural disasters, weather, human actions, forest fires, etc.

16. Limiting Factor (LF)
Most populations can adapt to a certain amount of change, but major upsets can lead to long-term declines in population sizes…
What might be the outcome of this?