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Recipe for the week of January 29 - February 4

CAM8 as an Ecomachine: 1 Predator, 2 Prey

This week's soup depicts one of our first CAM8-based ecology modeling experiments, as reported at the Santa Fe Institute workshop last month. A 512 by 512 array of 'patches' is populated by three species: the Good prey (benign), the Bad prey (pest), and the Ugly predator. These creatures move around, give birth to additional members of the same species on the same patch, and die. The birth, death and transport rates for a creature can all depend on the demographics of its patch. Without going into details, this framework permits the empirical investigation of a rich class of nonlinear competitive random CA dynamics. The performance of our simulation on CAM8 is about 400 times that of a Power Mac program, providing real-time interactive visualization of systems large enough to exhibit complex spatial structure.

The color scheme for our implementation is unforgettable. The Good guys are green, every ecologist's favorite color. The pests are blue meanies, and the bloodthirsty predators are red. Our three species inhabit each patch with one of four densities: zero, low, medium or high, with the intensity of their colors adjusted accordingly, and with mixed populations being represented in standard RGB coordinates. For instance, bright yellow corresponds to a patch with a high density of predators and benign prey but no pests. Our soup shows the state of the ecology a few hundred time steps after a small density of predators has been introduced into an equilibrium of good and bad prey in which the pests predominate. At this early stage, wave fronts of the predators reminiscent of simpler 'forest fire' dynamics are clearly visible.

One interesting story connected with this experiment may be viewed as a cartoon of biocontrol. For certain parameter values discovered by Eric Klopfer, it turns out that the pests predominate in the absence of predators, the predators are unable to eliminate the pests in the absence of good prey, but the pests can be eliminated without seriously impacting the good prey if all three species are present. We plan to report on further developments with this model, a corresponding two-predator, one-prey system, and other Ecomachine simulations in future recipes.

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