Periodic solutions to a delayed predator-prey model with Hassell-Varley type functional response

In this paper, a delayed predator-prey model with Hassell-Varley type functional responses is studied. Some sufficient conditions are obtained for the existence of positive periodic solutions to it by applying the coincidence degree theorem. It is interesting that the result is based on the delay, which is different from the previous work (the results are delay-independent). Furthermore, the simulation shows that some conditions are sharp. (C) 2010 Elsevier Ltd. All rights reserved.