1P. A. Abrams and J. D. Roth, The effects of enrichment of three-species food chains with nonlinear functional responses, Ecology 75 (1994) 1118 -1130.
2D. Bainov and P. Simeonov, Impulsive Differential Equations: Periodic Solutions and Applications (Longman Scientific and Technical, Harlow, 1993).
3M. Bohner and A. Peterson, Dynamic Equations on Time Scales: An Introduction with Applications (Birkh:user, Boston, MA, USA, 2001).
4M. Bohner and A. Peterson, Advances in Dynamic Equations on Time Scales (Birkhguser, Boston, MA, USA, 2003).
5Y. Chen, Multiple periodic solutions of delayed predator prey systems with type IV functional responses, Nonlinear Anal. Real World Appl. 5 (2004) 45-53.
6C. H. Chiu and S. B. Hsu, Extinction of top predator in a three-level food-chain model, J. Math. Biol. 37 (1998) 372- 380.
7G. H. Cui and X. P. Yan, Stability and bifurcation analysis on a three-species food chain system with two delays, Commun. Nonlinear Sci. Numer. Simulat. 16 (2011) 3704 -3720.
8H. Fang, Existence of at least two periodic solutions for a competition system of plankton allelopathy on time scales, J. Appl. Math. 2012 (2012) 602679, 14 pp.
9R. Gaines and J. Mawhin, Coincidence Degree and Nonlinear Differential Equations (Springer-Verlag, Berlin, 1977).
10J. G. P. Gamarra and R. V. So16, Complex discrete dynamics from simple continuous population models, Bull. Math. Biol. 64 (2002) 611 -620.