Complexity and Complex Ecological Systems is an extension of Elsevier’s 2021 book Complexity and Complex Chemo-Electric Systems directed toward the analysis and synthesis of diverse ecological processes running in heterogeneous macrosystems. Contemporary advanced techniques such as averaged analysis, food webs approaches, and classical optimization results along with some numerical algorithms are commonly used in ecosystems. This book treats ecological systems as specific functional integrities. In Complexity and Complex Ecological Systems, one can observe how various types of ecological heterogeneities can contribute to flows of living and inanimate parts of the moving pseudo-continuum. This book is a valuable reference for scientists, engineers, and graduate students of environmental, chemical, and biological engineering, helping them better understand complex macroscopic systems and enhance their technical skills in theoretical and practical research.