01 December 2011


Definition: An ecosystem is shorthand for “ecological system.”  Although the ecosystem is often erroneously referred to as a level of ecological organization, it is in reality a concept that applies to many difference scales.  Ecosystems were originally defined to consist of a biotic complex, that is, the aggregation of plants, animals, and microbes, along with a physical complex, that is the soils, waters, materials, climate, and environmental conditions and signals, all encompassed within a stated spatial boundary. 

Examples: An ecosystem may consist of a bit of organic matter and decomposer organisms in a flask on a laboratory bench, or the mosses, bacteria, and fungi on a decomposing log in a Pacific Northwest US forest, or to the entire biosphere of the Earth, which includes the biologically active layers of the oceans, atmosphere, and continents and the flows of energy, materials, and influence among them.  Ecosystems may be self supporting, or autotrophic (“self feeding”), or they may require input of biologically fixed energy from outside their boundaries.  Ecosystems that require fixed energy from elsewhere are labeled as heterotrophic, or “other feeding.”  Urban ecosystems with their included suburbs and exurbs, are heterotrophic.  

Ecosystem Figure 1.  The basic ecosystem concept from biophysical ecology.  Each ecosystem has a boundary defined by the researcher.  Within that spatial area, organisms and physical factors interact, exchanging energy, nutrients, and wastes, and affecting the microclimatic conditions.  All natural ecosystems use energy from beyond their boundaries, and export waste heat that can no longer be used by organisms.  Almost all natural ecosystems also receive some materials from outside, and lose some materials to other ecosystems by erosion or leaching.  Ecosystems can be of any size.

Why important: The ecosystem concept, even though it can apply to any spatial size, is one of the most important ideas in modern ecology.  It indicates that the connections and transfers of material, energy, and influence among components of the natural world are the driving features of nature.  So it is with urban systems.  Cities, suburbs, exurbs, and indeed the entire metropolitan areas encompassing them can be considered to be ecosystems.  Such urban ecosystems are not necessarily autotrophic, or self sustaining, but each can incorporate components and processes that enhance sustainability.  Metropolitan ecosystems and their components are socio-ecosystems, which require biological, physical, and social expertise to understand and manage.

For more information:
·        Pickett, S. T. A. and J. M. Grove. 2009. Urban ecosystems: what would Tansley do? Urban Ecosystems 12:1-8.
·        Cadenasso, M. L., S. T. A. Pickett, and J. M. Grove. 2006. Dimensions of ecosystem complexity: heterogeneity, connectivity, and history. Ecological Complexity 3:1-12.
·        Grove, J. M. and W. R. Burch, Jr. 1997. A social ecology approach and applications of urban ecosystem and landscape analyses: a case study of Baltimore, Maryland. Urban Ecosystems 1:259-275.
·        Hagen, J. B. 1992. An entangled bank: the origins of ecosystem ecology. Rutgers University Press, New Brunswick.
·        Likens, G. E. 1992. The ecosystem approach: its use and abuse. Ecology Institute, Oldendorf/Luhe, Germany.
·        Golley, F. B. 1993. A history of the ecosystem concept in ecology: more than the sum of the parts. Yale University Press, New Haven.


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