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Definition of Ecology

Ecology was originally defined in the mid-19th century, when biology was a vastly different discipline than it is today.

Illustration by Ernst Haekel, 1904.

Our definition of ecology

Ecology is the scientific study of the processes influencing the distribution and abundance of organisms, the interactions among organisms, and the interactions between organisms and the transformation and flux of energy and matter.

Our definition is unique in that it emphasizes several things:

  • A starting focus on organisms, aggregations of organisms, or systems incorporating organisms or their by-products
  • The bounding of ecology by both the biological and physical sciences
  • The breadth of subject matters within ecology
  • The joint consideration of both biotic and abiotic aspects of nature
  • Depending on the ecological specialty, the focus can be on different proportions of biotic or abiotic aspects of nature 
  • The relationships between organisms and the physical world can be bidirectional, although different specialties may emphasize the effect of the organisms (and systems containing them) on the physical world, or the effect of the physical world on the organisms
  • The boundary between the abiotic and the biotic aspects of ecology is blurry
  • The disciplinary focus is on "processes", "interactions" and "relations" rather than on the physical entities per se

Ecology was originally defined in the mid-19th century, when biology was a vastly different discipline than it is today.

The original definition is from Ernst Haeckel, who defined ecology as the study of the relationship of organisms with their environment. In the intervening century and a half, other definitions of ecology have been proposed to reflect growth of the discipline, to found new specialties, or to mark out disciplinary territory.

There are three pervasive definitions of ecology

The first definition stems from the Haeckelian form -- the study of the relationship between organisms and environment.

The second definition, which is perhaps the most commonly repeated, considers ecology to be the study of the distribution and abundance of organisms (Andrewartha and Birch 1954).

The third definition focuses ecology on the study of ecosystems (Odum 1971).

The 3 kinds of definitions each have their limits and advantages. The hallmark of ecology is its encompassing and synthetic view of nature, not a fragmented view.

Our definition of ecology is a blend of the second and third definitions. This new overarching definition attempts to bridge the spectrum of ecological approaches, with the goal of promoting synthesis and integration.

1st definition

The classical Haeckelian definition emphasizes both the living and the non-living components of the natural world. However, as a reflection of its vintage, it emphasizes that organisms are the relevant manifestation of the biotic world.

The mid-19th century, with its largely macroscopic view of the world, neglected inconspicuous organisms, such as microbes, the chemical products of organisms in the environment, and ecological systems at larger scales or higher hierarchical levels than organisms.

2nd definition

Andrewartha and Birch (1954) reinforced the focus on the organism as the core of ecology. Their work clearly includes the abiotic environment as well as the biotic environment as factors influencing distribution and abundance.

This is shown by their recognition of the importance of climatic fluctuations, for example. However, in its application, the definition of Andrewartha and Birch has often been associated with a predominately biotic focus.

This definition has become somewhat of a rallying cry for community and population centered ecology. Clearly, this definition has not stimulated exploration of the frontier of ecology with the sciences of the physical environment.

3rd definition

Odum (1971) began with the Haeckelian definition, but his desire to establish a new kind of ecology -- ecosystem ecology -- led him further from that cornerstone than most.

He provided several statements of the scope of ecology, including the difficult-to-interpret statement that ecology was simply environmental biology. Truest to his brand of ecosystem thinking was his definition of ecology as the study of the structure and function of nature.

Although Odum's extreme reliance on emergent properties and resuscitation of superorganismic thinking have proven problematic to many ecologists, his loosening of the bonds of Haeckel's focus on the organism is useful.

The limits and advantages of the 3 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.