This textbook has been designed to meet the needs of B.Sc. Second Semester students of Zoology for the Panjab University, Chandigarh. Maintaining the traditional approach to the subject, this textbook not only provides strong conceptual understanding, but also helps in developing scientific outlook of the student. It comprehensively covers two papers, namely, Paper-I: Biodiversity & Ecology – I and Paper-II: Biodiversity & Ecology - II. The first part of the book discusses phylum Arthropoda with a detailed case study of periplaneta. Further, it explains social organization in insects and economically important insects. It also discusses the components and dynamics of ecosystem. Second part of the book provides a detail account of phylum Mollusca along with its the general introduction and case studies. Furthermore, it elucidates natural resources like renewable and nonrenewable natural resources and their conservations. This book also discusses the wildlife conservation including national park, sanctuary and IUCN red list.