Organism is the smallest unit of ecological study.

Organisation is the arrangement and coordination of small components into larger components in a hierarchy, where each level is formed of components of lower level and itself becomes constituent of still higher level

Hierarchy in aorganisation from the level of biomolecules to organismic level is called biological hierarchy or biological organisation. The hierarchy in the levels of organisation connected with ecological grouping of organism is called ecological hierarchy or ecological level of organisation

There are no sharp lines or breeks in the functional sense amongst various level of ecological hierarchy as the same individual is a components of population, biological community as well as ecosystem