In the model PRODSALE, renewable resources from the environment are used by the economy. Money received from environmentally derived sales or services is used to pay for the economic assets required to use the environment. For example, fishermen receive money to pay for their boats. See Figure IV-4a.

Another example is shrimp production from aquaculture shrimp ponds. Money (M) is necessary to buy the goods and services, operations, labor, shrimp food, fertilizer and maintaining the system assets. The pond system assets (A) include concrete, pipes and pumps. The success of the system depends on a low price for the goods and services (P2) and a high price for shrimp at the market (Pl) and is measured by the quantity of money accumulated (M).

If you start with the natural production of shrimp and enough money to build the pond system, the graph shows an increase in the money return as the completed ponds yield more shrimp (Figure IV-4b).

J is the inflow of the natural energies of the sun, rain, river water, and larvae in the water from the estuary. The equation for E indicates the goods and services available depend on the money account (M) and the prices (P2).

Examples of economic systems directly dependent on renewable resources

Similar pond systems using fresh water produce catfish and crayfish. Forestry operations yield nuts, fruits and logs. The assets in a logging operation would be the saws, rigs, trucks and huts necessary to get the logs cut and transported. This model could be used for agricultural production too. Tourist facilities near national parks are the assets for use of environmental esthetics.

"What If" Experimental Problems

1. What is the effect of the amount of money you start with? Try M = 50, then M = 1. What is the advantage of having 5 times more money: M = 500?
   


2. If the price of goods and services changes, what happens to your system? Try doubling the price, P2 = 1, and then make P2 = 1.5.
   


3. What happens to the business if the price of goods and services goes up 1% per year. Add statement 335: P2 = P2 + (0.01*P2)
   


4. How dependent is the success of your system on the price of shrimp (P1)? Try doubling the price and then halving it.
   


5. What happens to the business if the price of shrimp goes steadily down at 1% per year?
   


6. What happens if the environmental conditions for aquaculture increase (e.g. more sunlight)?

COMPUTER MINIMODELS AND SIMULATION EXERCISES FOR SCIENCE AND SOCIAL STUDIES

Howard T. Odum* and Elisabeth C. Odum+
* Dept. of Environmental Engineering Sciences, UF
+ Santa Fe Community College, Gainesville

Center for Environmental Policy, 424 Black Hall
University of Florida, Gainesville, FL, 32611
Copyright 1994

Autorização concedida gentilmente pelos autores para publicação na Internet
Laboratório de Engenharia Ecológica e Informática Aplicada - LEIA - Unicamp
Enrique Ortega
Mileine Furlanetti de Lima Zanghetin
Campinas, SP, 20 de julho de 2007