Fig. 5.

Phase plane for public goods interaction: collective antibiotic resistance. Trajectories are shown in purple, starting at dark purple points. Strain 1 produces an antibiotic-degrading enzyme at the cost of a slower growth rate. Blue and orange lines indicate the isoclines for total population size and composition. Blue and orange hatched areas indicate an increase in the corresponding variable. Parameters not indicated in the figure: $B_0/\mu =1.25$, ${\rho }_1/\alpha =5·{10}^{-3}$, $S_0\phi ={10}^5$, $\kappa =\gamma =2$