2.3: What is a model?

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Science strives for simplicity, and models are part of the process. What is a model? It is just a simplified view of something more complex.

The word “model” is used here essentially as it’s used in everyday English. For example, in ordinary English, “modeling clay” can be used to make simplified miniatures of three-dimensional images of animals, automobiles, buildings, or even full-scale three-dimensional images of objects like the human heart. A “model airplane” can be rendered to show at a glance the physical appearance of a large aircraft, and can even be constructed to ﬂy so as to test aerodynamics under proper rescaling. A “model organism” is a simpler organism that may respond to medical tests or treatments in ways similar to those of a more complex organism.

Even the fashion model on the runway meets this definition of a simplified view of something more complex. The infinite complexity of the human spirit is not relevant on the runway; all that is relevant in this context is the person as a realistic way to display fashions.

This book focuses on computational and mathematical models of ecological systems. What is left out of these models is as important as what is put in. Simplification is key.

If you have a complex natural system you don’t understand, and you construct a computer model incorporating everything you can about that natural system, you now have two systems you don’t understand. — after Chris Payola, UMN

A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away. — Antoine de Saint-Exupery

Two different simplifications of time are commonly used in ecological models:

Discrete time — Events happen at periodic time steps, as if time is non-existent in between.
Continuous time — Events happen smoothly and at all times.

In addition, there are two different classes of models:

Macroscale — Individual organisms are not tracked, but are measured in aggregate and represented by composite variables such as N.
Microscale — Individual organisms are tracked separately. These are also known as agent-based or individual-based models.

Macroscale models can be handled either by computers or mathematics, but microscale models are usually restricted to computers. Keep in mind that all four categories are only approximations of reality. Later in this book we will also explore mechanistic versus phenomenological models.