Dispersal of species to find new resources is an important part of
population dynamics. Migration rates can evolve in response to the
relative success of different dispersal strategies. A rigorous
mathematical analysis (Dockery, et al, 1998) showed that in a simplified
deterministic treatment of two species which differ only in their
dispersal rates the slow species always dominates. This would indicate that evolution
would always favor slow dispersal. We demonstrate that fluctuations in an
agent-based model can change this conclusion and can lead to dominance by the
fast species or to coexistence, depending on parameters. We discuss two different
effects of fluctuations, and show that our results are consistent with more
complex treatments that find that selected dispersal rates are not
monotonic with the cost of migration.
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