The Weasel Population

A resident on an island released several weasels a number of years ago. Current residents are concerned that the population is growing. You have researched the situation and uncovered the following:

• The current population of weasels is 500.
• Since this is an island any changes in population will be due to births and deaths.
• The annual birth rate on an island of this size will vary with the population. Due to limited food, the rate will go down as the population goes up. The equation is .9 minus the value of, .2 times the population divided by 3000.
• The annual death rate also varies with the size of the population. Due to overcrowding, it goes up as the population increases. The equation is .75 plus the value of, .25 times the population divided by 3000.

Develop a systems dynamics model for this system. Simulate the system for 50 years. Call this run1.

The model is...

What did you find? You should get growth to a stable population of 1,000.

Change the initial population to 1500 and run the model again (Call this run2.) What happens?

The population now falls to a stable population of 1,000.

This system contains one reinforcing feedback loop and three balancing loops. It exhibits the "growth to a goal" behavior - Why?

Note: This is a simplified model. It does not represent the actual behavior pattern of any animal population.

Save your final model as weasel.

Submit a copy of the .mdl file to Black Board under Weasel Lab by the end of lab today.