1. POPULATIONS

2. 3 Characteristics of populations
Geographic (Spatial) Distribution
Density
Growth Rate

3. Geographic (SPATIAL) Distribution
Dispersion – the pattern of spacing of a population within an area
3 types
Uniform
Clumped
Random

4. Uniform Distribution
Population is spread out evenly

5. Clumped Distribution
Populations gather in clumps

6. Random Distribution
Populations spread out randomly, forming clumps in some areas and uniformity in others

7. Density The number of organisms per unit area
Low density vs. High density

8. Growth Rate How fast does a given population grow? 2 main types
Exponential Growth
Logistic Growth

9. Exponential Growth
Occurs when the individuals in a population reproduce at a constant rate
The increase is slow at first. This is called the Lag Phase.
Over time the population becomes larger. This is called the exponential growth phase.
Under ideal conditions with unlimited resources, a population will grow exponentially

10. What does it look like?
A.K.A.
J- curve
Lag Phase

11. Logistics
When a population’s growth slows or stops following a period of exponential growth
Limited by availability of resources
Population growth may slow down when:
The death rate increases
The birthrate decreases
When resources (food, shelter, optimal temperature) are not available
When the carrying capacity is reached.
Carrying Capacity – the maximum number of organisms that can be supported by a given environment

12. What does it look like?
Carrying capacity
A.K.A.
S-curve

13. Factors that affect the population size
Number of Births
Number of Deaths
Number of Individuals that enter or leave a population

14. Limiting Factors Factors that cause population growth to decrease
Can be Density Dependent – depends on the # of organisms
Can be Density Independent – does not depend on the # of organisms

15. DDF: Competition
Crowded populations compete for food, shelter, water, sunlight
The more individuals in a given area, the sooner they will use up the available resources
Occurs between same species and also members of different species
Both species are under pressure to change (evolution) to occupy the separate niches
No two species can occupy the same niche, this is called competitive exclusion

16. DDF: Predation There are always more prey than predators
When this balance shifts, then competition for prey will result
Starvation may also be the result if prey is not available

17. DDF: Parasitism and Disease
Parasites range in size from microscopic, disease causing bacteria to tapeworm 30 cm or more in length
They take nourishment at the expense of their hosts, often weakening them and causing disease and death

18. Density Independent Factors
Unusual weather (storms or hurricanes)
Natural Disasters (earthquakes, volcanic eruptions)
Seasonal Cycles (Extreme hot or cold weather)
Human Activities (Damming rivers, clear-cutting forests, industrialization, hunting, fishing)