1. Populations
Biology A/Ecosystems

2. Intro to Populations
A population is a group of similar organisms that live in the same area.
Population density compares the number of organisms in the population to the space they occupy.

3. Population Size Three factors affect population size:
The number of births
The number of deaths
The number of organisms that enter or leave the population

4. Growth Rate Example
Watch the “Rat Attack” video clip and consider why the population of black rats was able to grow so quickly every 48 years.

5. Thinking about growth…
**Imagine that you are asked to consult for a major industrial powerhouse on ways that they can reduce pollution to meet state and federal standards. They offer two options on how you can get paid.
Option A: You get $100,000 dollars cash upon completion of the project.
Option B: You get the end value of 1 penny per day doubled everyday for thirty days.

6. Option B Calculation 0.01 0.02 0.04 Day Pay Amount 1 11 21 2 12 22 313 23 4 14 24 5 15 25 6 16 26 7 17 27 8 18 28 9 19 29 10 20 30

7. Option B Calculation 30 5,368,709.12 Day Pay Amount 1 0.01 11 10.24 21
10,485.76 2
0.02 12
20.48 22
20,971.52 3
0.04 13
40.96 23
41,943.04 4
0.08 14
81.92 24
83,866.08 5
0.16 15
163.84 25
167,722.16 6
0.32 16
327.68 26
335,544.32 7
0.64 17
655.36 27
671,088.64 8
1.28 18
1,310.72 28
1,342,177.28 9
2.56 19
2,621.44 29
2,684,354.56 10
5.12 20
5,242.88 30
5,368,709.12

8. Exponential Growth
This kind of quickly increasing growth is called exponential growth.
Exponential growth can occur in populations of organisms also (like the human population!)
However, exponential growth CANNOT continue for a long time.

9. Causes of Exponential Growth
Two things can cause exponential growth:
Constant rate of reproduction (no predators or disease)
Unlimited resources (plenty of space and food)
When graphed, exponential
growth looks like a J

10. Think Pair share
What are two possible reasons that a population will not continue to increase exponentially forever?

11. Limiting Factors
Limiting Factors = Factors that cause the growth of a population to slow down or stop.
Biotic Limiting Factors = living limiting factors examples: predators, limited food
Abiotic Limiting Factors = non-living limiting factors
examples: drought, disease

12. Causes of Logistic Growth
Two things can cause logistic growth:
1. Decreasing rate of
reproduction (due to
predators or disease)
2. Limited resources (not
enough space or food)
When the graph of growth changes from a J- shaped curve to an S-shaped curve, this shows logistic growth.

13. Carrying Capacity
If a population becomes to large, there is not enough food, water or shelter for all of the organisms.
Ultimately, any ecosystem can only support a certain number of organisms in each population.
The number of organisms that a certain ecosystem can support is called the carrying capacity.

14. Graphing Carrying Capacity
Carrying capacity is represented by the horizontal line that the graph never stays above:
Use the graph to answer the following questions:
1. What type of growth occurs between 1800 and 1850?
2. Label the carrying capacity on the graph.
3. What type of growth curve is shown in the graph?