1. Factors Affecting Populations
SBI4U
Miss Richardson

2. Regulating Populations
Theoretically, populations can continue to grow
However, they are limited by many factors such as carrying capacity, fecundity and density dependent and density independent factors

3. Density Independent Factors
Factors that affect the population regardless of the density are called density-independent factors. 
Examples of this are natural disasters and weather.

4. Density Dependent Factors
Populations that follow logistic growth are limited by density-dependent factors
These are biotic factors
The impact on the population is dependent on how dense the population initially is
As populations reach the carrying capacity, they are influenced even more

5. Density-Dependent Factors: Competition
Intraspecific competition: competition between members of the same species for resources

6. Density-Dependent Factors Competition
Interspecific competition: competition between different species for resources
Competition exclusion principle – when 2 species compete for the same resource they cannot co-exist
Allee effect – occurs when populations get too small and individuals cannot find a mate
Minimal viable population – smallest number of individuals that ensures a population can exist

7. Density-Dependent Factors: Predation
Carnivores limit the growth of the prey population

8. Density-Dependent Factors: Predation
Predator-prey interactions result in population cycles where the size fluctuates over time
This results in sinusoidal growth

9. Density-Dependent Factors: Predation
Organisms have developed a variety of defence mechanisms for survival
Camouflage
Chemical defence
Mimicry

10. Symbiosis
Symbiosis is an interspecific relationship that means to live together
There are 3 symbiotic relationships
Parasitism
Commensalism
Mutualism

11. Parasitism
This is when one organism benefits and the other is harmed, but not killed. 
An example is a tapeworm living in a human.

12. Commensalism
This is when one organism benefits and the other is not harmed. 
For example a fungus is growing on a tree, but the tree is not harmed.

13. Mutualism This is when both organisms benefits.
For example this humming bird is extracting nectar while the flower is being pollinated.