Electronic Journal of Differential Equations, Vol. 2009(2009), No. 76, pp. 1-10. Title: Hopf bifurcation for simple food chain model with delay Authors: Mario Cavani (Univ. de Oriente, Cumana, Venezuela) Teodoro Lara (Univ. Rafael Rangel, Trujillo, Venezuela) Sael Romero (Univ. de Oriente, Cumana, Venezuela) Abstract: In this article we consider a chemostat-like model for a simple food chain where there is a well stirred nutrient substance that serves as food for a prey population of microorganisms, which in turn, is the food for a predator population of microorganisms. The nutrient-uptake of each microorganism is of Holling type I (or Lotka-Volterra) form. We show the existence of a global attractor for solutions of this system. Also we show that the positive globally asymptotically stable equilibrium point of the system undergoes a Hopf bifurcation when the dynamics of the microorganisms at the bottom of the chain depends on the history of the prey population by means of a distributed delay that takes an average of the microorganism in the middle of the chain. Submitted May 11, 2009. Published June 16, 2009. Math Subject Classifications: 34D99 Key Words: Simple food chain model; Hopf bifurcation; Holling type I; attractor.