And the hawks left foodless will follow soon after

334^	_	Section 3 Artificial Intelligence

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Depending on how the demo is set up, and to some degree blind luck, most demos end in one of two ways. The most likely outcome is what amounts to ecologi-cal disaster—the sparrows eat all the flies or the hawks eat all the sparrows. If all the flies die off, the sparrows also eventually die too from lack of food, and the hawks (left foodless) will follow soon after. If the sparrows all die because the hawks are just a bit too good at what they do, the hawks will eventually die as well, leaving a world filled with nothing but flies and obstacles. This seemed to happen quite a bit in most of my tests.

Another possibility is a sort of stasis between the sparrows and flies. The hawks might all die off dirough bad luck and not finding any sparrows to eat. If this hap-pens, the sparrows will live on, feeding on the flies for an indefinite period. They might eventually kill off flies, which puts us back into the first scenario described ear-lier, but a balance is also possible, with the flies reproducing just fast enough to keep all the sparrows fed and happy.

3.11 Flocking with Teeth: Predators and Prey 335

selves, particularly if one were to try to adopt this code for a game. Although only flies can reproduce in the demo, it's a simple matter to allow both sparrows and hawks to do so. Another potential improvement that could help "close the loop" ecology-wise might be to give the flies something to feed on as well, perhaps hawk feathers.

Finally, an excellent book that addresses the topic of artificial life in general, in addition to discussing both flocking and boids, is Steven Levy's Artificial Life [Levy93].

References

[ReynoldsOO] Reynolds, Craig, maintains an extensive reference on flocking and steering behavior at www.red3d.com/cwr/boids/ and has presented a wide variety

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