Permanence and periodicity of a delayed ratio-dependent predator–prey model with stage structure

A periodic ratio-dependent predator–prey model with time delays and stage structure for both prey and predator is investigated. It is assumed that immature individuals and mature individuals of each species are divided by a fixed age, and that immature predators do not have the ability to attack prey. Sufficient conditions are derived for the permanence and existence of positive periodic solutions of the model. Numerical simulations are presented to illustrate the feasibility of our main results.  2004 Elsevier Inc. All rights reserved.