Figure 7. Results from the ABM model demonstrate the effects of using continuous space and allowing competition for space among mussels. The system size was 20x20 and the default parameters of Table 1 were used. The diameters of the filled circles are proportional to the sizes of the mussels. (A) The spatial distribution of mussels at the upper equilibrium for the mean field approximation when each prey is confined to a grid point. (B) The spatial distribution of mussels at the upper equilibrium for the mean field approximation when space is continuous and mussels grow until they touch another individual. In this case, a recruitment limit was put on the total number of mussels allowed in the system because given the small size of recruits and the high immigration rate, without this the system would quickly be swamped by hundreds of thousands of individuals. The total number of mussels in the system was capped at 150% of the number predicted by the ODE approximation. The ODE prediction of a lower and upper stable equilibrium also holds when the assumption of grid-based space is relaxed. The histograms in (C) and (D) show the size distribution of mussels for the plots in (A) and (B). See Donalson et al. (2003, 604KB) for details.