1. Aim: What things determine the size of a population?
Monday, February 25, 2019
Aim: What things determine the size of a population?

2. Objectives At the end of this lesson you should be a
Explain and identify the factors an effect on the carrying capacity of an ecosystem for a given population.

3. Quick Review
Monday, February 25, 2019
An ecosystem is an area where living things (biotic) interact with nonliving things (abiotic).
Biotic factors:
Plants, animals, populations, Predator/prey, mates
Abiotic factors:
Air (oxygen/CO2), water, temperature, pH, shelter
Populations are a group of the same species

4. What determines the size of a population?
Monday, February 25, 2019
What determines the size of a population?
The size of a population is determined on how much resources are available.
These resources can be biotic or abiotic.
If there is plenty of food, organisms will produce more offspring. Increasing the population. (biotic)
If there are few mates, there will be more competition resulting in a smaller population. (biotic)
If there are more shelters available, more organisms can build homes. The population increases. (abiotic)
If there is a shortage of water, there will be an increase in competition resulting in a smaller population. (abiotic)

5. What determines the size of a population? (cont)
Monday, February 25, 2019
Under natural circumstances populations will not continue to increase indefinitely.
This is because as populations grow there is an increased demand for resources.
If there is plenty of food, organisms will produce more offspring. But that also means there is an increased need for water and shelter. (forcing a reduction of the population)
If there are more shelters available, more organisms can build homes. But that also means there is an increased need for water and mates. (forcing a reduction of the population)
This limit in which an environment places of a population is known as the environment’s carrying capacity.

6. Monday, February 25, 2019
Dynamic equilibrium -a state of homeostasis in which conditions change over time, but always stay close to a certain value.
Dynamic equilibrium is the up and down line in a graph.
The population fluctuates (goes up and down) around the carrying capacity.
Carrying capacity – is the average point that an environment can support a population.
Time
# organisms
Dynamic equilibrium
carrying capacity

7. Why do population fluctuate?
Monday, February 25, 2019
Why do population fluctuate?
Population Size
When an population is introduced to an area, there is plenty of resources, so the population increases
There is a point where there is not enough resources to support the growing population – individuals begin to die – decreasing the population
The middle or average between the hills and valleys (ups and downs) is called the carrying capacity
This pattern remains the same as long as the resources are available – This is a cycle
There is a point where there is enough resources to support the decreasing population – more offspring are born– increasing the population
Time

8. Why do populations fluctuate?
Monday, February 25, 2019
Why do populations fluctuate?
Within any given area, there is a limited number of resources.
This limit in the amount of resources is known as limiting factors.
3. Predators/Prey
4. Other conditions:
-Temperature
-pH
-ability of decomposers to remove/recycle wastes
Space
Availability of resources:
-water/food
-amount of sunlight
-minerals in soil
-oxygen/carbon dioxide

9. Why are Limiting Factors Limiting?
Monday, February 25, 2019
Why are Limiting Factors Limiting?
Organisms need many different resources to live (Food, Water, Shelter).
As organisms use these resources, the resources need to be replenished or they will be all used up.
If the resource become used up faster than it is replenished, those organisms that once used them will begin to die out.

10. Monday, February 25, 2019
Fact If

11. Monday, February 25, 2019 If

12. The Balance between Prey and Predator
Monday, February 25, 2019
The Balance between Prey and Predator
Sometimes a population can be a limiting factor for another population.
In a predator / prey relationship, the size of one population influences the size of the other.
The more prey - the more food for the predator- the more babies the predators make.
The more predators – the more prey they eat – population of prey decrease.
The less prey – there is not enough food for the predators to eat – predator population decreases.
The less amount of predators – more prey survive to reproduce making more babies.

13. Competition
Monday, February 25, 2019
Both space and the availability of resources are affected by competition.
less space, less resources = More competition
Those that are best fit will survive, while those that are least fit will die.

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June 2005

15. Monday, February 25, 2019
If both species started out with the same amount of space and resources, why is there a difference in their populations?

16. Monday, February 25, 2019