Dang Vu GiangYongwimon LenburyHanoi Institute of MathematicsMahidol University2018-07-122018-07-122008-02-01Mathematical and Computer Modelling. Vol.47, No.3-4 (2008), 259-265089571772-s2.0-38149035164https://repository.li.mahidol.ac.th/handle/20.500.14594/19144Recently, we investigated the effect of delay on the asymptotic behavior of the model over(x, ̇) + x = f (x ({dot operator} - τ)) of population growth, when the nonlinearity f is a unimodal function. Now we prove that for large delay, there are several nonconstant (positive) periodic solutions. We also use knots theory to study periodic solutions with period 3 τ. Some of our results do not rely on the continuity of f and thus are applicable to wider range of biological problems in which the growth functions are piecewise continuous. © 2007 Elsevier Ltd. All rights reserved.Mahidol UniversityComputer ScienceDecision SciencesEngineeringMathematicsArticleSCOPUS10.1016/j.mcm.2007.04.002