Dimensional approaches to designing better experimental ecosystems: a practitioners guide with examples.

Enclosed, experimental ecosystems ("mesocosms") are now widely used research tools in ecology. However, the small size, short duration and often simplified biological and physical complexity of mesocosm experiments raises questions about extrapolating results from these miniaturized ecosystems to nature. Dimensional analysis, a technique widely used in engineering to create scale models, employs "compensatory distortion" as a means of maintaining functional similarity in properties and relationships of interest. An earlier paper outlined a general approach to applying dimensional analysis to the construction and interpretation of mesocosm experiments (Petersen and Hastings in Am Nat 157:324, 2001). In this paper we use examples, largely drawn from the aquatic literature, to illustrate how dimensional approaches might be used to maintain key ecological properties. Such key properties include effective habitat size, environmental variability, vertical and horizontal gradients, and interactions among habitats. We distinguish both continuous and discrete approaches that can be used to achieve functional similarity through compensatory distortion. In addition to its potential as a tool for improving the realism of experimental ecosystems, the dimensional approach points towards new options for developing, testing and advancing our understanding of scaling relationships in nature.