  In this paper we consider a model of a nutrient-prey-predator system in a
chemostat with general functional responses, using the input concentration of
nutrient as the bifurcation parameter. We study the changes in the existence of
isolated equilibria and in their stability, as well as the global dynamics, as
the nutrient concentration varies. The bifurcations of the system are
analytically verified and we identify conditions under which an equilibrium
undergoes a Hopf bifurcation and a limit cycle appears. Numerical simulations
for specific functional responses illustrate the general results.
