1. Ch 4: Population Biology
4.1 Population Dynamics

2. Principles of Population Growth
Section 4.1
Principles of Population Growth
Lets Calculate the number of bacteria there would be if the population were allowed to grow for 24 hours.
Assume that there were two to start with, they divide once every 20 minutes, and none of them died.
What factors might keep them from taking over the world?

3. How do Populations Grow?
Section 4.1
How do Populations Grow?
Linear Growth
Suppose you work at a some job
You get paid $10 per hour
How much would you have in 10 hours?
This is NOT how populations grow

4. How do Populations Grow?
Section 4.1
How do Populations Grow?
Exponential Growth
The initial phase of population growth is slow because the number of available organisms is limited at first.
Soon the growth becomes very fast as the organisms reproduce.
J shaped curve – unchecked growth
Is growth unlimited?
2, 4, 8, 16, 32, 64, 128, 256, 512

5. Limits of the Environment
Section 4.1
Limits of the Environment
Can a population of organisms grow indefinitely?
Limiting factors
Space to grow
Availability of food
The number of organisms that an environment can support is called the Carrying Capacity.

6. Carrying Capacity Section 4.1
The graph of the carrying capacity is a S curve.
Populations start out slow and then experience a period of exponential growth, followed by a stabilizing growth rate.
Populations go above the carrying capacity then fall below, only to rise above again.

7. Carrying Capacity Section 4.1
If the population overshoots carrying capacity, limiting factors will come into effect and deaths will exceed births and the population will fall below carrying capacity.

12. Patterns of Population Growth
Section 4.1
Patterns of Population Growth
Why do some populations of organisms seem to thrive at certain times of the year and then dwindle at other times?
In order to answer this question biologists study the reproductive pattern (aka life history pattern) of animals.

13. Ranges of Population Growth
Section 4.1
Ranges of Population Growth
Two extreme organisms for population growth rates are elephants and mosquitoes.
Mosquitoes are rapid reproducers over a short time.
Elephants are slow reproducers over a long time.

14. The Mosquito Strategy Section 4.1
Mosquitoes are successful in environments that are unpredictable and unstable.
Organisms with this type of life-history pattern tend to:
Be small
Mature rapidly
Reproduce early
Have a short life span

15. The Elephant Strategy Section 4.1
Organisms that tend to live in a more stable environment have a different life-history pattern. They tend to:
Be large
Reproduce and mature slowly
Live for long periods of time.

16. Why the Different Types of Reproductive Cycles?
Section 4.1
Why the Different Types of Reproductive Cycles?
The type of reproductive pattern that an organism has depends on the environment they are in.
Limiting factors in an environment can be biotic or abiotic and may include limited food supply, space, chemicals, temperatures …
How organisms are dispersed can also be important.

18. The number of organisms per unit area
Chapter 4
Population Ecology
Population Density
The number of organisms per unit area
Spatial Distribution
Dispersion is the pattern of spacing of a population.

19. Dependent on the availability of resources such as food.
Spatial Distribution
3 types of dispersion
Dependent on the availability of resources such as food.
Neutral interactions between organisms
Competing for a resource; territories
Plant, bat, resources clumped

20. Two Limiting Factors that affect Dispersal
Section 4.1
Two Limiting Factors that affect Dispersal
Density-Dependant
E.g. Disease, Competition, Parasites, Food
(effects get bigger as population size increases)
Density-Independent
Temperature, Storms, Floods, Drought
(effects not influenced by population size – mostly abiotic)

24. Organism Interactions
Organism Interactions Limit Population Size
Population sizes are also controlled by interactions among organisms that share a community -- biotic factors

25. Predation Affects Population
Section 4.1
Predation Affects Population
The population of the prey in a community will affect the population of the predators.
Likewise the opposite is true.
This relationship is referred to as the Predator-Prey Relationship
e.g. Lynx and Hare
Predation increases the chance that resources will be available for the remaining individuals in a prey population!

26. Competition for Resources
Section 4.1
Competition for Resources
The more organisms in the same population you have struggling for the same resource the less resources there are for each individual organism.
Competition for resources such as food, water and territory increases with increased population = density dependent

27. Crowding and Stress Section 4.1
As a population grows the amount of stress increases in a population.
Stress can cause:
Aggression
Decrease in parental care
Decreased fertility
Decreased resistance to disease