Welcome to the simulated ecosystem Wator!

Introduction:

This is an implementation of Wator, an ecosystem resembling natural predator-prey interaction; this Cellular Automaton delivers similar results to those of the Lotka-Volterra equation.
I got the idea from and refer for further information to:
A.K. Dewdney
Sharks and fish wage an ecological war on the toroidal planet Wa-Tor
(Scientific American, December 1984)

Cellular Automata

Well, in a strict sense, Wator is not a CA since the 'cells' - fishes and sharks - move around... so better see life for that

Wator - rules:

In every timestep every fish calculates its behaviour according to this rules (it has one internal variable: pregnancy):

• move to a randomly chosen free place in the Moore-Neighbourhood (left,right,up,down and the diagonals)
• if pregnant time (user parameter) is reached leave a new fish at the old place and reset pregnancy counter else
• increase pregnancy counter

In every timestep every shark calculates its behaviour according to this rules (it has two internal variables: starving & pregnancy):

• if starving counter equals starve value (user parameter) die else
• if any fish neighbours move to a randomly field, eat the fish and maybe (see above) leave a child, else
• increase the starving counter and follow the fish movement/pregnancy rules

From those easy rules a great diversity of macro behaviour can emerge. With 'good' parameters you should be able to generate fluctuations in the populations, that is: There are just few sharks and thus the number of fishes explodes - but now no shark has to die of hunger and thus the population of shark grows, eating up all fish and now lot of sharks die of hunger... All this behaviour can be observed in nature, too - and the Lotka-Volterra equation shows the same wavelike population fluctuations.
I plan to integrate Lotka-Volterra in the WatorApplet to allow for better comparison.
Like with Lotka-Volterra the system is very much depended on the initial settings - small changes in -say- the number of fishes at the beginning might leed to a completly different behaviour (the system might be come into another basin of attraction - see CalResCo for an introduction to dynamic systems)

Click here to watch the webdemo To get the ecosystem running try to paste some fishes by clicking on the 'water' at first and start the Simulation to see how they crowd the landscape. Before it gets boring pause the simulation, add a shark and continue. To prevent the ecosystem from colapsing you should increase the grid to -say- 100x100
(size for appr. 800x600, I suggest to download the files and run them alone to be able to resize the window and yield some speed)