The existence of positive periodic solution of a generalized semi-ratio-dependent predator-prey system with time delay and impulse is studied by using the continuation theorem based on the coincidence degree theory. The permanence of the system is also considered. The results partially improve and extend some known criteria. §1 Introduction As Cushing [4] pointed out that it is necessary and important to consider models with periodic ecological parameters or perturbations which might be quite naturally exposed (for example, those due to seasonal effects of weather, food supply, mating habits, hunting or harvesting seasons, etc.). In recent decade, there have been many works which are devoted to the studies of dynamical behaviors for predator-prey systems with various functional responses, including the permanence of system, the existence, uniqueness and global attractivity of positive periodic solution and so on. Along this direction, one can refer to [3,[6][7][8][9][11][12][13]18,26,28] and the references cited therein.In particular, many authors have explored a class of semi-ratio-dependent predator-prey system. In 2003, Wang et al. in [27] studied the following semi-ratio-dependent predator-prey system1) and established some criteria for the existence of positive periodic solution. In 2005, Huo in [19] further considered system (1.1) and improved some results obtained in [27] by dropping some assumptions. Recently, Fazly and Hesaaraki in [15], Fan and Wang in [14] considered the following discrete analogue of system (1.1)
2)Received: 2009-02-03. MR Subject Classification: 34C25, 92D25.