Ecological Structures
Life and the Earth's Environment
What is Life?
Materials for Life
Capturing Energy for Life
Evolution & the Environment
Disruptive Forces on Ecosystems
Measurement of Impact on Ecosystems
Sustainability & Ecological Integrity
Approaches to the Natural Environment
Global and Regional Scales
Global Agreements
Philosophies for Sustainability
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Ecosystems and Structure
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Ecosystems and Structure

One can think of living organisms in terms of an organization with various levels of structure. Ecology is the study of the patterns and relationships of these systems. The word "oikos" means "house" in Greek and "logos" means "pattern." The word "oecologie" was coined by Ernest Haeckel, German scientist and follower of Darwin, in 1866. Since then and throughout the 1890's European botanists studied systems of plants and land and their interdependencies, giving rise to the science of ecology. Thus the science of ecology has always had a holistic approach top nature, connecting communities and systems. The philosophical roots of ecology and the land ethic of Aldo Leopold are discussed in detail in the unit on Ethical Systems.

The early study of ecology was tilted towards moral philosophy. As a science, it grew in parallel, more as a description of the distribution of plant communities, and their patterns of succession. In the 1920's and '30's ecology became more of a discipline of science. In 1927, Charles Elton, a colleague of Aldo Leopold, coined phrases such as "food chain" and "niche" and began to work on the way nutrition started with the sun, and on the natural dependencies of organisms and "communities of plants." The English ecologist Arthur Tansley, reflecting that the land community was anthropomorphic, proposed "ecosystem" for the system of relationships.

The following discussion describes each of the main levels, however it does not go all the way back to the most minute level of cells and genes. These structured levels are terminology that you need to be familiar with to start discussing the role of ecology in environmental issues.

Ecosystems: living and nonliving components of an area that includes the habitat and the physical and chemical environment. The classic definition of an ecosystem was stated in 1953 by Odum: any unit that includes all organisms (i.e., community) in a given area interacting with the physical environment so that a flow of energy leads to a clearly defined structure, biotic diversity, and materials cycles. The point is that a balance is reached.

Species: A particular group of the same organism that depends on an optimum range of each environmental factor such as light, pH, nutrients, food, water, competitors, predators, etc. These ranges should overlap within a particular location. Some of these environmental factors are more critical than others.

Population: several members of the same species in a particular area at the same time and genetically distinct from other populations of that species.

Community: different species interacting together, forming a distinct system that includes the food web. Note that the habitat is where the community lives. For example, a wetlands habitat is defined as an area often covered by shallow water, or one where the ground is wet long enough to support plants specialized to grow under saturated conditions.

Biome: several habitats together in a particular climatic area e.g. tropical rainforest versus coniferous rain forest.

Biosphere: highest organizational level in which life exists that ranges from several thousand meters into the atmosphere, and to depths of the oceans including land masses.

Source: Clark, Mary E. Ariadne's Thread. St. Martin's Press, New York, 1989.
Reprinted with permission of Macmillan Ltd..




  ©Copyright 2003 Carnegie Mellon University
This material is based upon work supported by the National Science Foundation under Grant Number 9653194. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.