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This book provides cutting-edge results on the existence of multiple positive periodic solutions of first-order functional differential equations. It demonstrates how the Leggett-Williams fixed-point theorem can be applied to study the existence of two or three positive periodic solutions of functional differential equations with real-world applications, particularly with regard to the Lasota-Wazewska model, the Hematopoiesis model, the Nicholsons Blowflies model, and some models with Allee effects. Many interesting sufficient conditions are given for the dynamics that include nonlinear characteristics exhibited by population models. The last chapter provides results related to the global appeal of solutions to the models considered in the earlier chapters. The techniques used in this book can be easily understood by anyone with a basic knowledge of analysis. This book offers a valuable reference guide for students and researchers in the field of differential equations with applications to biology, ecology, and the environment.

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Chapter 1. Introduction.- Chapter 2. Positive Periodic Solutions of Nonlinear Functional Differential Equations with Parameter .- Chapter 3. Multiple Periodic Solutions of a System of Functional Differential Equations.- Chapter 4. Multiple Periodic Solutions of Nonlinear Functional Differential Equations.- Chapter 5. Asymptotic Behavior of Periodic Solutions of Differential Equations of First Order.- Bibliography.

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"This book presents various results on the existence and stability of periodic solutions for first order scalar functional differential equations. ... This book is written in a clear and concise style and offers a valuable reference guide for students and researchers interested in the study of periodic solutions for functional differential equations." (Adriana Buica, zbMATH 1312.34002, 2015)

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