Dynamics of the Higgins-Selkov and Selkov systems

We describe the global dynamics in the Poincaré disc of the Higgins-Selkov model x′=k0−k1xy2,y′=−k2y+k1xy2,where k0, k1, k2 are positive parameters, and of the Selkov model x′=−x+ay+x2y,y′=b−ay−x2y,where a, b are positive parameters. We determine the regions of initial conditions with biological meaning.