Artificial Life VI

Models in Evolutionary Ecology and the Validation Problem

C. C. Maley


All models of natural systems represent an abstraction and simplification of that system. Thus all models suffer a validation problem. Should we believe that the results of the model have any bearing on reality? This is a particularly acute problem for Alife models of evolution and ecosystems. The time scale of evolution and the complexity of ecosystems make controlled experiments difficult. If Alife is ever to contribute significantly to biology, we must find methods by which we can build confidence in our models. One alternative to experimental tests of a model is to validate it against previously verified theory. I have applied a series of ecological validation tests to a model of species diversification. Examination of the predator-prey dynamics, trophic cascades, competitive exclusion, adaptation, and the species-area curve in the model has shown that a course grained spatial structure was inadequate to capture the realistic dynamics of an ecosystem. Only when spatial structure was extended to the local patch dynamics did the model begin to behave realistically under a wide range of parameters. Validation of the ecological dynamics of the model provides indirect support for the evolutionary behavior of the species within the ecosystem.

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