Electronic Journal of Differential Equations,
Vol. 2012 (2012), No. 199, pp. 1-13.

Title: Necessary and sufficient conditions for the existence of 
       periodic solutions in a predator-prey model on time scales
 
Authors: Xingyong Liu (South China Normal Univ., Guangzhou, China)
         Xiuxiang Liu (South China Normal Univ., Guangzhou, China)

Abstract:
 This article explores the existence of periodic solutions for non-autonomous
 impulsive semi-ratio-dependent predator-prey systems on time scales.
 Based on a continuous theorem in coincidence degree theory, sharp sufficient
 and necessary  conditions are derived in which most popular monotonic,
 non-monotonic and predator  functional responses are applicable.
 This article extends the work in [6,10,12,13,134,18,25].

Submitted July 16, 2012. Published November 15, 2012.
Math Subject Classifications: 34A34, 34C25, 92D25.
Key Words: Time scales; periodic solutions; predator-prey system;
           functional responses.