1. Factors that affect populations

2. What aspects of the ecosystem can limit the population of a species?
Anything that changes the relationship between births, deaths, immigrations and emigrations will change the overall population size.
A limiting factor = a factor that causes population growth to decrease
Some limiting factors include:
Access to resources
Competition
Predation
Parasitism and disease
Drought and other climate extremes
Human disturbances

3. Limiting Factors There are 2 main categories of limiting factors:
Density-dependent factors- factor that depends on the size of the population to act
Density-independent factors- affect all populations in similar ways, regardless of population size

4. Density-Dependent Factors
A limiting factor that depends on population size including:
Intra and interspecific Competition – organisms struggle for resources
Predation – predator-prey relationship controls population of both the predator and the prey
Parasitism – control population by weakening/killing host. Less hosts= less parasites as well.
Disease - control population by weakening/killing host
Density dependent factors become limiting only when the population density (number of organisms per unit area) reaches a certain level
These factors operate most strongly when a population is large and dense

5. Competition
As resources become more scarce competition for that resources increases
With greater competition, there is a larger struggle for survival
It becomes more likely that a given individual will not succeed.

6. Intraspecific Competition

7. Predator-Prey Relationship
The number of predators and prey in a system are directly related
Predators increase- Prey decreases
Prey decreases- predator decreases
Predator decreases- prey increases
Prey increases- predator increases

8. Disease

9. Density-Independent Factors
Affect all populations in similar ways, regardless of the population size including:
Unusual weather
Natural disasters
Seasonal cycles
Human activities (damming rivers/clearing forests)
Many species will show a characteristic “crash,” then the population will build back up right away, or stay low for some time
Environments are always changing, and most populations can adapt to a certain amount of change by growing or shrinking in size.
Major upsets in the ecosystem can lead to long-term declines in certain populations (human activities)

10. Density Independent- Extreme Weather

11. Seasonal

12. Human Activities
Overexploitation of cod fishery- grand banks