Fig. 7. Population dynamic model of agricultural regime shifts.
a. Assuming a simple linear relationship between the environment (which is, in this context actually a technology of production) and the population density. Because of the way the sustainable curve crosses the necessary one, the equilibrium is stable. If the crossings were to be reversed , the point would be unstable.
b. Making the sustainable curve nonlinear results in two alternative equilibria separated by a saddle point. The dotted lines indicate the basins of attraction of the two equilibria (From Vandermeer 2009).