General Instructions for Simulations

General Instructions for Simulations

Initial Population (N0): Initial number of organisms

Range: 0 – infinity

Birth Rate: Proportion of population born each year (density-dependent)

Range: 0 – 1 (can be higher in real life)

0 = no babies born each year

0.1 = 10 babies born per 100 organisms each year

1.0 = 100 babies born per 100 organisms each year

Death Rate: Proportion of population that dies each year (density-dependent)

Range: 0 – 1

0 = no deaths each year

0.1 = 10 deaths per 100 organisms each year

1.0 = 100 deaths per 100 organisms each year

Immigration: Number of organisms that come into a population from another area. (density-independent)

Range: 0 – infinity

Emigration: Proportion of population that leaves to another area each year. (density-dependent)

Range: 0 – 1

0 = no individuals leave each year

0.1 = 10 organisms leave per 100 organisms each year

Growth Rate (r): proportional increase (or decrease) of a population.

Calculated as birth rate – death rate – emigrations

Growth Rate > 0 …. increase in population

Growth Rate = 0 …. No change in population size

Growth Rate < 0 …. Decrease in population

Carrying Capacity (K): maximum number of individuals (of a particular species) that an environment can sustain.

Range: 0 – infinity

Computer Modeling of Population Growth

Open the file called “Population Simulation Models.xls” (in T:\Biology location). Open the tab labeled “Exponential Growth.”

Exponential Growth Model

I.  Enter the following parameters into the “Exponential Growth Model”

N0 = 10

Birth Rate = 0.5

Death Rate = 0.2

Immigration, Emigration = 0

1.  What is the population size after 50 years? ______

2.  Increase N0 to 100. Now change N0 to 1000.

1. What is the population size after 50 years in each case?

N0 = 100: ______N0 = 1000: ______

1. What happens to the shape of the graph in each case?

II.  Enter the following parameters into the “Exponential Growth Model”

N0 = 10

Birth Rate = 0.6

Death Rate = 0.2

Immigration, Emigration = 0

3.  a. What is the population after 50 years? ______

b.  How does this compare to the population size compared to the one reported in question #1? Explain.

4.  a. Change the birth rate to 0.7 and the death rate to 0.3. Now what is the population size after 50 years?

b. Explain why this population size is either similar to or different from the one reported in question #3a?

III.  Enter the following parameters into the “Exponential Growth Model”

N0 = 1000

Birth Rate = 0.2

Death Rate = 0.5

Immigration, Emigration = 0

5.  What is the growth rate (r) of this population? ______

6.  Is the population growing or shrinking? ______

7.  After how many years does this population go extinct? ______

IV.  Additional

8.  Which of the following scenarios would show an exponential population increase?

1. When there are unlimited resources available.
2. When the population is well below the carrying capacity for its environment.
3. The increase in the global population of humans on Earth over the last 1000 years.
4. All of the above

Logistic Growth Model

Open the tab labeled “Logistic Growth Model” and enter the following parameters into the spreadsheet:

N0 = 10

Birth Rate = 0.45

Death Rate = 0.41

Immigration, Emigration = 0

Carrying Capacity (K) = 500

9.  What is the population size after 50 years? ______

10.  Now change the death rate to 0.3. Sketch and describe the graph below:

11.  Now change the death rate to 0.2. Sketch and describe the graph below:

12.  How long does it take for this population to reach the carrying capacity in the environment described in question #12?

13.  Describe what happens to the growth of the population as the population size approaches the carrying capacity?