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Scenario

The island kingdom of Viti Levu had a rat problem. The king hired Dr. Muller to develop a poison to kill the rats. In addition, the king set up a more stringent inspection process for arriving ships to ensure that no more rats were introduced to the island. After months of research, Dr. Muller successfully designed a poison to which the vast majority of rats (85%) were susceptible. Within days of applying the poison, the rat population plummeted. The king declared the problem solved, island residents celebrated, and Dr. Muller left the island with a big check. However, within a year, the rat population became as big as ever. The king was confident that no rats had come to the island from boats. In retrospect, it appears that the rat population which was mostly easily killed with poison earlier on had become largely resistant to the poison a year later.

Question 1:

The story about Viti Levu identified several factors that were affecting the population of rats on the island, and there could be many more factors that were not explicitly identified in the story. Identify at least one key stock in this situation. Then identify all key inflows and outflows affecting that stock and explain how those flows are impacting the stock. Be sure to provide enough detail to illustrate your understanding of the difference between stocks and flows.

Question 2

We have talked about how feedback loops can influence the behavior of a complex system. Identify one feedback loop. Describe the variables included in the loop, including the impact they have on each other (e.g., an increase in Variable A causes an increase in Variable B). Identify the feedback loop as either positive (i.e., reinforcing) or negative (i.e., balancing). Include enough detail to illustrate you understand what a feedback loop is and the difference between positive and negative feedback loops.

Question 3

We know that populations of organisms become resistant to poisons through the process of natural selection. In this case, although most (85%) of the rats were initially killed by the poison, some (15%) of the rats were naturally less susceptible to the poison and survived to breed. Over the course of the year, most of the rats on the island became resistant to the poison. How can you describe changes in the rat population over time by referring to the actions of slow-changing and fast-changing variables? Be specific as to which variables are slow-changing or fast-changing and how they act on the rat population.

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