Fig. 3. Net rate of change for a single region vs. pollutant level for two rates of input to region 1. Blue: the pollution rate for region 1 (M1) = 1.6; red: M1 = 1.9). Circles denote stable points. The pollutant level in the other region was fixed at 1.6. Other parameters: M2 (the pollution rate in region 2) = 0.75; D (the transport rate between regions) = 0.1; c (the decay rate) = 0.05; s (the maximum sequestration rate) = 0.5; m (the pollutant level at which sequestration is half the maximum rate) = 5; q (which determines the slope of f(P) near P) = 6. P stands for amount of pollutant, and f(P) scales the sequestration to the amount of pollutant.