Figure 5. Two spatial effects are observed in the CA model when the mean field assumptions are relaxed. Each plot shows the size distribution of mussels over space, where mussel sizes are color coded from blue for the smallest through red for the largest. The size distributions over space are shown for the mean field approximation (h = ∞) at (A) the lower and (B) the upper equilibria. (C) When the neighborhood size is small (h = 1) and the sea star attack rate is reduced (q = 0.85), “islands” of larger individuals develop at the lower equilibrium. (D) When a smooth linear gradient in the sea star attack rate is imposed from q = 0 at the upper boundary of the lattice to q = 2 at the lower boundary and the mean field approximation (h = ∞) is used, the lattice equilibrates at the upper equilibium. (E) When the same gradient in q is combined with a small neighborhood effect (h = 1), the result is a sharp transition in prey cover similar to what is seen in many natural mussel beds. This predation gradient is what might be expected from differences in foraging times at different tidal heights. See Donalson et al. (2003, 604KB) for details.