Predator

dy/dt = δxy - γy

The predator population growth δxy depends on successful kills and the reproduction rate; however, delta is likely be different from beta. The loss rate, an exponential decay, of the predators {\displaystyle \displaystyle \gamma y}γy represents either natural death or emigration

​This model attempts to understand the behavior of average lifetime of companies in the S&P500 index. The reference mode for the model is a graph available at this link: https://static-cdn.blinkist.com/ebooks/Blinkracy-Blinkist.pdf (page 5) which was discussed in the System Thinking World Discussion forum.

Mergers & Acquisitions can be one of the reasons for older companies to be replaced with newer companies in the Index. With M&A of older companies, the empty slots are taken over by newer companies. However, overtime, these new companies themselves become old. With steady M&A, the stock of older companies decreases and stock of newer companies increases. The result is that average age of the companies in the S&P Index decreases.

The oscillations in the diagram, according to me, is due to oscillations in the M&A activity.

There are two negative feedback loops in the model. (1) As stock of new companies increases, the number of companies getting older increases which in turn decreases the stock. (2) As M&A increases, stock of older companies decreases which in turn decreases M&A activities.

Limits of the model

The model does not consider factors other than M&A in the increase in number of new companies in the Index. New companies themselves may have exceptional performance which will result in their inclusion in the Index. Changes in technology for example Information Technology can usher in new companies.

Assumptions

1. It is assumed that M&A results in addition of new companies to the Index. There could be other older companies too, which given the opportunity, can move into the Index. Emergence of new technologies brings in new companies.

Based on a dialogue on the System Dynamics mailing list regarding the current level of acceptance of System Dynamics after it has been promoted for over 40 years I dredged up the following set of influences as a thought exercise. This is an example of a Drifting Goals Systems Archetype.

Visão geral

O modelo mostra a conexão e o conflito da indústria entre o turismo florestal e o turismo de montanha em Derby, Tasmânia. O objetivo desta simulação é descobrir o ponto de equilíbrio para a coexistência.

Como funciona o modelo?

Ambas as indústrias podem fornecer contribuições económicas para a Tasmânia. Em primeiro lugar, a venda de madeira através da exploração madeireira geraria renda. Além disso, os gastos dos ciclistas de montanha gerariam renda. No entanto, a baixa taxa de regeneração das árvores não pode encobrir a exploração madeireira, o que influencia as belas vistas e as experiências dos ciclistas. Embora a satisfação e a expectativa dependam das opiniões e da experiência, a demanda pelo mountain bike também seria influenciada pelas visitas repetidas e pelo boca a boca.

Informações interessantes

Embora a silvicultura possa fornecer uma grande contribuição económica para a Tasmânia, o excesso de exploração madeireira vai contra a estrutura ESG, além de criar conflito com o turismo de montanha. Desde que o número de visitas de cavaleiros seja estável, o turismo pode sempre proporcionar uma maior contribuição económica em comparação com a silvicultura. Portanto, o governo deveria considerar o ponto de equilíbrio entre as duas indústrias.