Simulistics

Fractal model of tree branching

Fractal branching models - frequently called Lindemeyer or L-system models - work by repeated application of the same branching rules. The Simile implementation uses a population submodel for the branch segments (intenodes), starting off with a single member (the base segment). An association submodel is used to define the relationship between one segment and its two daughters.

The behaviour of the model is visualised using a specially-developed display tool, showing the 3D structure of the simulated tree from the side and from the top.

Individual-based tree model

This model uses a population submodel to represent the trees in a forest stand. A simple, single-compartment model is used to simulate the growth of each tree, and this is summed outside the submodel to give the total volume of the stand of trees. The model also sets the initial number of trees in the population, the rate at which new trees are created, and the rule for killing off trees when they reach a certain size.

Individual-based model of population dynamics

This shows how amazingly simple it is to make an individual-based model of population dynamics in Simile. We simply create a population submodel, add in symbols for the initial number, birth and death. In this model, the probabilities of reproduction and death are age-dependent, and reproduction also depends on the total population size, which is simply obtained by summing the number of individuals.

Population age-class models

Explicit compartments

The simplest way of making an age-class model is to have a separate compartment for the number in each class. The compartments are connected by flows representing the movement of animals between classes as they age. Reproduction feeds into the first class, and all classes have a mortality outflow. This particular model includes density-dependent reproduction.

The model eventually equilibrates with a fixed number in each class.

You can use this page to get a quick overview of the wide range of models that can be constructed in Simile. Each entry gives some text on the model, a model diagram (usually an outline view for all but the simplest of models), and a sample screen display from the running model. Models are arranged roughly in order of increasing complexity and increasing sophistication of the Simile techniques used.

Classic (Lotka-Volterra) population dynamics

Exponential population growth