Levels of Organization in an Ecosystem from the smallest to the largest:
Organism or Species
Population
Community
Ecosystem
Species are the different kinds of organisms found on the Earth. A more exact definition of species is a group of interbreeding organisms that do not ordinarily breed with members of other groups.
A population comprises all the individuals of a given species in a specific area or region at a certain time.
Community refers to all the populations in a specific area or region at a certain time. Its structure involves many types of interactions among species.
Ecosystems are dynamic entities composed of the biological community and the abiotic environment. An ecosystem's abiotic and biotic composition and structure is determined by the state of a number of interrelated environmental factors.
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