The limits and advantages of the three definitions of ecology:

The positive side of the first definition is that it is simple and it emphasizes both biotic and abiotic aspects of nature. On the negative side is its overemphasis on the organism as the focus. Haeckelian statements should always be cast as the study of relationships rather than the study of organisms in relation to environment. The difference in emphasis may appear to be minor, but it indicates the deficiency of Haeckel's definition. The second definition is positive in its emphasis on quantifiable and unambiguous parameters, but it falls short because it omits a range of critical ecological subjects. To its credit, the third definition is not restricted to patterns or organisms and recognizes that ecology is about processes. All of the definitions take organisms as their starting point. However, they are not in all cases explicit that ecology can consider all manner of systems (in the broadest sense) that include organisms and their products.

The three definitions have limits or connotations imposed by their vintage and history of use. Haeckel operated in a time when biology was dominated by focus on organisms as anatomical, physiological or taxonomic subjects. Many of the modern concerns of ecology, and indeed of biology, were far in the future when Haeckel wrote. Odum was concerned with the justification of ecosystem ecology as an academic specialty. He highlighted ways in which ecology differed from other university departments in the immediate post-World War II era.

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