Experimental Manipulation of Model Ecosystems

  • Robert G. Wetzel
  • Gene E. Likens


Ecosystems have been described as the “functional units of the landscape” (Odum, 1971), where organisms interact with their physical-chemical environment and with other organisms. For limnologists, lakes, ponds, streams, and rivers and their associated drainage basins represent the ecosystems of interest. However, these ecosystems are large and complex, and thus it is difficult to decipher the various interactions that occur within them.

Natural ecosystems are exposed continuously to changing environmental conditions, of both internal and external types. These conditions can be changed either by natural (for example, seasonally) or by unnatural means (e.g., through human intervention). Whatever the cause, the effects of any single change may be difficult to separate from those resulting from all of the other changes that are occurring simultaneously. A changing natural ecosystem can be likened to an experiment in which the investigator is trying to control and, at the same time, understand many known and unknown variables. For the creative scientist, this situation can present a real challenge. Nevertheless, the understanding of causation in the ecosystem rarely can be delineated without the benefit of some carefully designed and rigorously controlled experimental work.

The cost in both money and time of doing experimental work on whole ecosystems often is prohibitive. Moreover, while such studies have been done [see, for example, Hasler and Johnson (1954), Likens et al. (1970), and Schindler (1974)], we usually do not have the privilege of being able to alter or to disturb seriously an entire ecosystem for experimental purposes. A common solution is to recreate, in the laboratory, microecosystems or microcosms [see, for example, Warington (1851) and Beyers (1963)]. An ecosystem brought into the laboratory can mimic the natural ecosystem in some respects but will differ in others: a microcosm is a simplified ecosystem with discrete boundaries. The scales of events in both time and space are abbreviated. Succession to a new steady state takes place in weeks, rather than in years. Microcosms generally have fewer species than do natural ecosystems and have, in consequence, simpler communities of organisms. Some characteristics of microcosms make them valuable objects of study. Microcosms are expendable, and the experimenter has control over the environmental boundary conditions to a degree impossible to achieve in the field. Also, it generally is assumed that the investigator can establish reproducible or replicable units, thereby allowing statistical evaluation of the data obtained from experimental treatments and controls for each manipulation.

In this exercise, two different approaches, the chemostat and the microcosm, will be described for the study of ecosystems in the laboratory. Both of these approaches require several weeks for stabilization, manipulation, and evaluation. Thus students should select one of these approaches and should understand that appreciable time must be allotted for independent study of these systems. The chemostat requires somewhat more sophisticated equipment and procedures.


Experimental Manipulation Natural Ecosystem Model Ecosystem Seed Shrimp Culture Chamber 
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  1. Barlow, J.P., W.R. Schaffner, F. deNoyelles, Jr., and B. Peterson. 1973. Continuous flow nutrient bioassays with natural phytoplankton populations, pp. 299–319. In:Bioassay Techniques and Environmental Chemistry. Ann Arbor Science Publ., Ann Arbor, MI.Google Scholar
  2. Beyers, R.J. 1963. The metabolism of twelve aquatic laboratory microecosystems. Ecol. Monogr. 33:281–306.CrossRefGoogle Scholar
  3. Beyers, R.J. 1964. The microcosm approach to ecosystem biology. Amer. Biol. Teacher 26:491–498.CrossRefGoogle Scholar
  4. Beyers, R.J. 1965. The pattern of photosynthesis and respiration in laboratory microecosystems. pp. 63–74. In:CR. Goldman, Editor. Primary Productivity in Aquatic Environments. Mem. Ist. Ital. Idrobiol. 18 Suppl. Univ. of California Press, Berkeley.Google Scholar
  5. deNoyelles, F. and W.J. O’Brien. 1974. The in situ chemostat—a self-contained continuous culturing and water sampling system. Limnol. Oceanogr. 19:326–331.CrossRefGoogle Scholar
  6. Hasler, A.D. and W.E. Johnson. 1954. Rainbow trout production in dystrophic lakes. J. Wildl. Manage. 18:113–134.CrossRefGoogle Scholar
  7. Herbert, D., P.J. Phipps, and D.W. Tempest. 1965. The chemostat: Design and instrumentation. Lab Prac. 14:1150–1161.Google Scholar
  8. Likens, G.E. 1985. An experimental approach for the study of ecosystems. J. Ecol. 73:381–396.CrossRefGoogle Scholar
  9. Likens, G.E., F.H. Bormann, N.M. Johnson, D.W. Fisher, and R.S. Pierce. 1970. Effects of forest cutting and herbicide treatment on nutrient budgets in the Hubbard Brook watershed-ecosystems. Ecol. Monogr. 40:23–47.CrossRefGoogle Scholar
  10. Odum, E.P 1971. Fundamentals of Ecology. 3rd Ed. W.B. Saunders, Philadelphia. 574 pp.Google Scholar
  11. Schindler, D.W. 1974. Eutrophication and recovery in experimental lakes: Implications for lake management. Science 184:891–899.CrossRefGoogle Scholar
  12. Warington, R. 1851. Notice of observation on the adjustment of the relations between animal and vegetable kingdoms. Quart. J. Chem. Soc., London 3:52–54.CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York 2000

Authors and Affiliations

  • Robert G. Wetzel
    • 1
  • Gene E. Likens
    • 2
  1. 1.Department of Biology, College of Arts and SciencesUniversity of AlabamaTuscaloosaUSA
  2. 2.Institute of Ecosystem Studies, Cary ArboretumThe New York Botanical GardenMillbrookUSA

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