1 Samuel M. Scheiner and Michael R. Willig, eds. 1. A General ...

groups, colonies, or symbiotic systems, or to coevolved multispecies systems. From this
perspective, the model is not general at all. It is just one in a collection of complementary, and
sometimes interacting or overlapping, models. By having a narrow scope, the model can be
reasonably realistic if parameters are estimated for a limited natural universe. Still, models of
populations, or interactions among populations in different contexts, are a major stronghold of
theory in ecology.
By contrast, ecosystem models are often developed for specific natural systems (Fitz et
al. 1996). Such models rely on general physical principles to account for the energy and material
budgets and on biological relationships to provide system specific and local contents. They can
be quite realistic, at least this is the intention of the investigators, but attempts to make them
general would require stripping biological contents and so removing these models from the
domain of ecology. In any case, I believe that ecology has benefited from developing and
accumulating ecosystem models in several ways such as building bridges to cybernetics and
engineering, providing management tools (e.g., adaptive management – Holling 1978), and
explicitly incorporating the abiotic environment into the dynamics of ecological systems.
Still another category of models appears to be driven by the need for precision. In an
attempt to explain species rank-abundance distributions ecologists developed a number of
statistical models. They are judged by the precision with which they describe actual collections
of data. In the absence of a good theory about underlying mechanisms, these models cannot be
seen as general. In fact, these models seem to work well in particular situations only, for
example, large data sets from undisturbed habitats generally follow a log-normal model of
abundance distribution. Different may models apply to disturbed habitats or small data sets. As
these models do not make good explicit links to underlying processes, they can hardly be seen as
realistic, even when they provide a precise fit to the data.
It is surprising, and it holds some promise, that some of the early, potentially important,
concepts have not advanced theoretically for over 100 years. Forbes’ microcosm embodied the
idea of wholeness and relative autonomy. He articulated, early on, a central notion that the
ecological world exists in the form of aggregates of interdependent parts. In his view, this
aggregation would be responsible for the emergence of partially bounded systems whose
components with a appreciable ability to adjust internally to each other. It is rather surprising
that this idea, while often invoked in the context of conservation, has not developed theoretically
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