This textbook presents a systematic account of the history of ecology’s development, its subject matter, objects of study, objectives, and research methods. It examines key environmental factors and their influence on organisms, major living environments, and organismal adaptations; it also covers biological rhythms, life forms, and biotic interactions between organisms. The text provides a detailed analysis of the ecological characteristics of populations, biogeocenoses, ecosystems, and the biosphere—including their structure, component composition, metabolism, energy flow, and the cycles of water and oxygen—and characterizes the biological and geological cycling of substances in nature.