The science of ecology has two complementary facets; study of the hierarchies of organisation, the classic reductionist classificatory method, and the construction of theories about relationships.
Odum (1983) writes;
The organised state of life is maintained by a continuous but step wise flow of energy. Thus dividing up a graded series or hierarchy into components is in many cases arbitrary, but sometimes subdivisions can be based on natural discontinuities. Because each level in the biosystem spectrum is “integrated” or interdependent with other levels, there can be no sharp lines or breaks in a functional sense, not even between organism and population.
The individual organism, for example, cannot survive long without its population, any more than the organ would be able to survive as a self perpetuating unit without its organism. Similarly, the community cannot exist without the cycling of materials and the flow of energy in the ecosystem. (Odum)
An important consequence of hierarchical organisation is that as components or subsets are combined to produce larger functional wholes, new properties emerge that were not present at the level
EMERGENT PROPERTY or NONREDUCIBLE PROPERTY cannot be predicted from the study of the components of that level or unit. Though findings at one level aid in the study of the next level, they never completely EXPLAIN the phenomena occurring at the next level, which must itself be studied. (Odum; author’s emphasis).
When hydrogen and oxygen are combined in a certain molecular configuration, water is formed, a liquid with properties utterly different from those of its gaseous components. When certain algae and coelenterate animals evolve together to produce a coral, an efficient nutrient cycling system is created that enables the combined system to maintain a high rate of productivity in waters with a very low nutrient content. Thus the fabulous productivity and diversity of coral reefs are emergent properties found only at the level of the reef community. (Odum)
Living organisms and their nonliving (abiotic) environment are inseparably interrelated and interact upon each other. Any unit (a biosystem) that includes all the organisms that function together (the biotic community) in a given area interacting with the physical environment so that a flow of energy leads to clearly defined biotic structures and cycling of materials between living and nonliving
parts is an ecological system or ecosystem. (Odum).
FIEBLEMAN 1954 has theorised that at least one new property emerges with each integration of subsets into a new set. (Odum).