1. Populations and Communities

2. Population Growth
Population: group of the same species that live in the same area in a given time.
If living conditions are IDEAL, growth will be exponential… there is nothing to inhibit growth!
In reality – exponential growth is not sustainable – there will always be a limiting factor
Can you think of an exception to this??

3. Logistic Growth
Real growth curves will eventually reach a steady state = the carrying capacity of the environment for that species
A population cannot continue to grow forever because of:
Lack of food
Overcrowding (lack of space)
Competition within the population

4. Factors that control population growth
Density-Dependent
Limiting Factors:
Factors that affect large and/or overcrowded populations
Density-Independent Limiting Factors:
Weather and natural occurrences that have nothing to do with the density of a population

5. Density-Dependent Limiting Factors
1. Competition (for food, space, water, sunlight…)
Remember: if two species compete for the same niche, one will lose. Natural selection allows for both species to survive if one species evolves and adapts to a different niche

6. Density-Dependent Limiting Factors
2. Predation
Predator-prey relationships keep both populations in balance
As prey pop. increases… the predator pop. will increase… as predator pop. increases, prey pop. will decrease… as prey pop. decreases, predator pop. will decrease… this allows prey pop. to increase… and the cycle begins again

7. Density-Dependent Limiting Factors
3. Parasitism
Parasites: live off host organism without killing it
Thrive best in large, stressed populations (stressed populations are susceptible to disease)
More easily spread in overcrowded populations

8. Density-Dependent Limiting Factors
4. Crowding and Stress
Smaller area per animal in which to find home and/or hunt for food
Crowded populations tend to fight

9. Interactions within and between Communities
Community: all the populations that live together within an area.
They live together – therefore they interact
Interactions include:
Competition
Predator/prey relationship
Symbiosis

10. Ecosystems are Connected!
Ecosystems are studied as isolated systems BUT
All ecosystems are interconnected by
Proximity
Migratory patterns
Atmosphere (wind patterns)
Hydrology of Earth (groundwater flows, rivers)

11. THE END!