Simpler (one variable) Model: Set $A = R$

$${\frac {dA}{dt}} = V_A\frac{A^2}{K_A+A^2} +A_0 -d(\rho)A.$$ (13)

Figure: Plot of ${\frac {dA}{dt}} = \frac{V_AA^2}{K_A+A^2} +A_0 -d(\rho)A$ as a function of $A$ for several values of $\rho$ with parameter values $V_A = 1.0, K_A = 1.0, A_0 = 0.05, \delta = 0.5, k_E = 0.1, k_A = 0.02$.