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Class XII Biology, Unit X chapter 13, Organisms and Populations, , Organisms and its environment:, > Ecology isthe branch of biology, which studies the interactions among organisms and, their physical (abiotic) environment., > The term Ecology was first coined by Emst Hackel.in 1869., > Ecology has two main branches. They are —, , 1) Autecology (Species Ecology): The study of reciprocal relationships between, every stage of development of a population or species and its environment is, called Autecology., , 2) Synecology: It is the study of reciprocal relationships between composition,, organisation and development of communities and their environment., , > Ecology is basically concerned with four levels of biological organisation. They are , 1) Organism: It is a distinct living entity which carries out all life processes in its, body. tis basic unit of ecological hierarchy. E.g., Man, cat, dolphin, etc., , 2) Population: The sum total of all individuals of a species in a specific, geographical area., , 3) Biological Community: Assemblage of all the populations of different species, present in an area that interact among themselves., , , , 4) Biome: It is a large unit, which consists of a major vegetation type, associated, fauna in a particular climatic zone. E.g., Tundra, tropical rainforest, deciduous, forest, deserts, etc., , , , Important terms of Ecology:, , Ecosystem: It represents the organisms and their environment in a particular area that interacts, with each other, , Habitat: It refers to a specific place or locality delimited by a combination of factors, physical, features and barriers where a community dwells., , Niche: The ecological niche of an organism represents the physical space occupied by it, the, resources it utilizes and its functional role in the ecological system., , Biosphere: The surface of earth with all life forms, ie union of all ecosystems., , Environment: Itis the surrounding area where organisms live. Ecology at organism level deals,, with how different organisms are adapted to their environment in terms of their survival and, reproduction.